Re: [PATCH 08/11] vfs: Merge check_submounts_and_drop and d_invalidate
"J. Bruce Fields" writes: > On Tue, Feb 25, 2014 at 02:03:36PM -0800, Eric W. Biederman wrote: >> "J. Bruce Fields" writes: >> >> > On Mon, Feb 24, 2014 at 04:01:29PM -0800, Eric W. Biederman wrote: >> >> Miklos Szeredi writes: >> >> >> >> > >> >> > You can optimize this by including the negative check within the above >> >> > d_locked >> >> > region and calling __d_drop() instead. >> >> >> >> For this patch just moving the code and not changing it is the corret >> >> thing to do because it helps with review and understanding the code. >> >> >> >> There are two ways I could see going with optimizing the preamble. >> >> Simply dropping the d_lock from around the d_unhashed test as a pointer >> >> dereference should be atomic, and the test is racy against >> >> d_materialise_unique. >> > >> > Could you explain? What's the race, and what are the consequences? > > Actually I was just confused as to whether the above was "is racy" was > claiming the existance of some bug. > > I believe I should have read the above as more like "the test is already > racy against d_materialise_unique, but it's a harmless race, and > dropping the d_lock wouldn't make it any worse". > >> >> (We don't always hold the parent directories inode mutex when >> >> d_invalidate is called). >> >> d_unhashed is not a permanent condition because of d_materialise_unique, >> and d_splice_alias. >> >> d_invalidate can be called on an unhashed dentry in one of two ways >> (either d_revalidate dropped the dentry or another routine that drops >> the dentry beat the current invocation of d_invalidate to the job). >> >> >> There are 3 places d_revalidate is called. >> >> Once on the rcu path with with the appropriate flag set. >> >> Once without out the parent i_mutex held, just off of the rcu path, >> on that path d_invalidate is when d_revalidate fails. >> >> Once during lookup with the parent directory i_mutex held. >> >> >> Because the parent direcories i_mutex is not always held accross >> d_revalidate and the following d_invalidate it happens that d_invalidate >> is not always an atomic operation. >> >> >> At worst the race results in a dentry that is dropped when it could be >> hashed, > > Because somebody not holding the i_mutex calls d_invalidate based on old > information and unhashes something that > d_materialise_unique/d_splice_alias just hashed? More likely today somebody not holding i_mutex and not in rcu context calls d_revalidate. d_revalidate drops the dentry and before we d_invalidate d_materialise_unique/d_splice_alias rehashes it. After my changes it looks like it takes 3 processes two instances of d_invalidate and a instance of d_materialise_unique/d_spliace_alias to trigger this case. In either case the window is very small and the outcome is effectively harmless. So I don't see this as a problem. >> that we will resurrect next time someone attempts to look it >> up and d_materialise_unique/d_splice_alias is called. > > OK. > >> None of that really matters for optimizing d_invalidate, but it is part >> of the background in which d_invalidate lives. All that is significant >> in d_invalidate is knowing that d_materialise_unique, and possibly >> d_splice_alias may run concurrently with d_invalidate. It is unlikely >> and essentially harmless. >> >> >> After my patchset (because I removed all of the d_drop's from >> .d_revalidate) the only race that should remain is between two parallel >> calls of d_invalidate. Which probably means we can remove the test for >> d_unhashed altogether. >> >> Right now I just want to make this first big step and make certain the >> code is solid. After that optimization is easy. > > Thanks for the explanation! Welcome. Eric -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH 08/11] vfs: Merge check_submounts_and_drop and d_invalidate
On Tue, Feb 25, 2014 at 02:03:36PM -0800, Eric W. Biederman wrote: > "J. Bruce Fields" writes: > > > On Mon, Feb 24, 2014 at 04:01:29PM -0800, Eric W. Biederman wrote: > >> Miklos Szeredi writes: > >> > >> > > >> > You can optimize this by including the negative check within the above > >> > d_locked > >> > region and calling __d_drop() instead. > >> > >> For this patch just moving the code and not changing it is the corret > >> thing to do because it helps with review and understanding the code. > >> > >> There are two ways I could see going with optimizing the preamble. > >> Simply dropping the d_lock from around the d_unhashed test as a pointer > >> dereference should be atomic, and the test is racy against > >> d_materialise_unique. > > > > Could you explain? What's the race, and what are the consequences? Actually I was just confused as to whether the above was "is racy" was claiming the existance of some bug. I believe I should have read the above as more like "the test is already racy against d_materialise_unique, but it's a harmless race, and dropping the d_lock wouldn't make it any worse". > >> (We don't always hold the parent directories inode mutex when d_invalidate > >> is called). > > d_unhashed is not a permanent condition because of d_materialise_unique, > and d_splice_alias. > > d_invalidate can be called on an unhashed dentry in one of two ways > (either d_revalidate dropped the dentry or another routine that drops > the dentry beat the current invocation of d_invalidate to the job). > > > There are 3 places d_revalidate is called. > > Once on the rcu path with with the appropriate flag set. > > Once without out the parent i_mutex held, just off of the rcu path, > on that path d_invalidate is when d_revalidate fails. > > Once during lookup with the parent directory i_mutex held. > > > Because the parent direcories i_mutex is not always held accross > d_revalidate and the following d_invalidate it happens that d_invalidate > is not always an atomic operation. > > > At worst the race results in a dentry that is dropped when it could be > hashed, Because somebody not holding the i_mutex calls d_invalidate based on old information and unhashes something that d_materialise_unique/d_splice_alias just hashed? > that we will resurrect next time someone attempts to look it > up and d_materialise_unique/d_splice_alias is called. OK. > None of that really matters for optimizing d_invalidate, but it is part > of the background in which d_invalidate lives. All that is significant > in d_invalidate is knowing that d_materialise_unique, and possibly > d_splice_alias may run concurrently with d_invalidate. It is unlikely > and essentially harmless. > > > After my patchset (because I removed all of the d_drop's from > .d_revalidate) the only race that should remain is between two parallel > calls of d_invalidate. Which probably means we can remove the test for > d_unhashed altogether. > > Right now I just want to make this first big step and make certain the > code is solid. After that optimization is easy. Thanks for the explanation! --b. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH 08/11] vfs: Merge check_submounts_and_drop and d_invalidate
On Tue, Feb 25, 2014 at 02:03:36PM -0800, Eric W. Biederman wrote: J. Bruce Fields bfie...@fieldses.org writes: On Mon, Feb 24, 2014 at 04:01:29PM -0800, Eric W. Biederman wrote: Miklos Szeredi mik...@szeredi.hu writes: You can optimize this by including the negative check within the above d_locked region and calling __d_drop() instead. For this patch just moving the code and not changing it is the corret thing to do because it helps with review and understanding the code. There are two ways I could see going with optimizing the preamble. Simply dropping the d_lock from around the d_unhashed test as a pointer dereference should be atomic, and the test is racy against d_materialise_unique. Could you explain? What's the race, and what are the consequences? Actually I was just confused as to whether the above was is racy was claiming the existance of some bug. I believe I should have read the above as more like the test is already racy against d_materialise_unique, but it's a harmless race, and dropping the d_lock wouldn't make it any worse. (We don't always hold the parent directories inode mutex when d_invalidate is called). d_unhashed is not a permanent condition because of d_materialise_unique, and d_splice_alias. d_invalidate can be called on an unhashed dentry in one of two ways (either d_revalidate dropped the dentry or another routine that drops the dentry beat the current invocation of d_invalidate to the job). There are 3 places d_revalidate is called. Once on the rcu path with with the appropriate flag set. Once without out the parent i_mutex held, just off of the rcu path, on that path d_invalidate is when d_revalidate fails. Once during lookup with the parent directory i_mutex held. Because the parent direcories i_mutex is not always held accross d_revalidate and the following d_invalidate it happens that d_invalidate is not always an atomic operation. At worst the race results in a dentry that is dropped when it could be hashed, Because somebody not holding the i_mutex calls d_invalidate based on old information and unhashes something that d_materialise_unique/d_splice_alias just hashed? that we will resurrect next time someone attempts to look it up and d_materialise_unique/d_splice_alias is called. OK. None of that really matters for optimizing d_invalidate, but it is part of the background in which d_invalidate lives. All that is significant in d_invalidate is knowing that d_materialise_unique, and possibly d_splice_alias may run concurrently with d_invalidate. It is unlikely and essentially harmless. After my patchset (because I removed all of the d_drop's from .d_revalidate) the only race that should remain is between two parallel calls of d_invalidate. Which probably means we can remove the test for d_unhashed altogether. Right now I just want to make this first big step and make certain the code is solid. After that optimization is easy. Thanks for the explanation! --b. -- To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH 08/11] vfs: Merge check_submounts_and_drop and d_invalidate
J. Bruce Fields bfie...@fieldses.org writes: On Tue, Feb 25, 2014 at 02:03:36PM -0800, Eric W. Biederman wrote: J. Bruce Fields bfie...@fieldses.org writes: On Mon, Feb 24, 2014 at 04:01:29PM -0800, Eric W. Biederman wrote: Miklos Szeredi mik...@szeredi.hu writes: You can optimize this by including the negative check within the above d_locked region and calling __d_drop() instead. For this patch just moving the code and not changing it is the corret thing to do because it helps with review and understanding the code. There are two ways I could see going with optimizing the preamble. Simply dropping the d_lock from around the d_unhashed test as a pointer dereference should be atomic, and the test is racy against d_materialise_unique. Could you explain? What's the race, and what are the consequences? Actually I was just confused as to whether the above was is racy was claiming the existance of some bug. I believe I should have read the above as more like the test is already racy against d_materialise_unique, but it's a harmless race, and dropping the d_lock wouldn't make it any worse. (We don't always hold the parent directories inode mutex when d_invalidate is called). d_unhashed is not a permanent condition because of d_materialise_unique, and d_splice_alias. d_invalidate can be called on an unhashed dentry in one of two ways (either d_revalidate dropped the dentry or another routine that drops the dentry beat the current invocation of d_invalidate to the job). There are 3 places d_revalidate is called. Once on the rcu path with with the appropriate flag set. Once without out the parent i_mutex held, just off of the rcu path, on that path d_invalidate is when d_revalidate fails. Once during lookup with the parent directory i_mutex held. Because the parent direcories i_mutex is not always held accross d_revalidate and the following d_invalidate it happens that d_invalidate is not always an atomic operation. At worst the race results in a dentry that is dropped when it could be hashed, Because somebody not holding the i_mutex calls d_invalidate based on old information and unhashes something that d_materialise_unique/d_splice_alias just hashed? More likely today somebody not holding i_mutex and not in rcu context calls d_revalidate. d_revalidate drops the dentry and before we d_invalidate d_materialise_unique/d_splice_alias rehashes it. After my changes it looks like it takes 3 processes two instances of d_invalidate and a instance of d_materialise_unique/d_spliace_alias to trigger this case. In either case the window is very small and the outcome is effectively harmless. So I don't see this as a problem. that we will resurrect next time someone attempts to look it up and d_materialise_unique/d_splice_alias is called. OK. None of that really matters for optimizing d_invalidate, but it is part of the background in which d_invalidate lives. All that is significant in d_invalidate is knowing that d_materialise_unique, and possibly d_splice_alias may run concurrently with d_invalidate. It is unlikely and essentially harmless. After my patchset (because I removed all of the d_drop's from .d_revalidate) the only race that should remain is between two parallel calls of d_invalidate. Which probably means we can remove the test for d_unhashed altogether. Right now I just want to make this first big step and make certain the code is solid. After that optimization is easy. Thanks for the explanation! Welcome. Eric -- To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH 08/11] vfs: Merge check_submounts_and_drop and d_invalidate
"J. Bruce Fields" writes: > On Mon, Feb 24, 2014 at 04:01:29PM -0800, Eric W. Biederman wrote: >> Miklos Szeredi writes: >> >> > >> > You can optimize this by including the negative check within the above >> > d_locked >> > region and calling __d_drop() instead. >> >> For this patch just moving the code and not changing it is the corret >> thing to do because it helps with review and understanding the code. >> >> There are two ways I could see going with optimizing the preamble. >> Simply dropping the d_lock from around the d_unhashed test as a pointer >> dereference should be atomic, and the test is racy against >> d_materialise_unique. > > Could you explain? What's the race, and what are the consequences? >> (We don't always hold the parent directories inode mutex when d_invalidate >> is called). d_unhashed is not a permanent condition because of d_materialise_unique, and d_splice_alias. d_invalidate can be called on an unhashed dentry in one of two ways (either d_revalidate dropped the dentry or another routine that drops the dentry beat the current invocation of d_invalidate to the job). There are 3 places d_revalidate is called. Once on the rcu path with with the appropriate flag set. Once without out the parent i_mutex held, just off of the rcu path, on that path d_invalidate is when d_revalidate fails. Once during lookup with the parent directory i_mutex held. Because the parent direcories i_mutex is not always held accross d_revalidate and the following d_invalidate it happens that d_invalidate is not always an atomic operation. At worst the race results in a dentry that is dropped when it could be hashed, that we will resurrect next time someone attempts to look it up and d_materialise_unique/d_splice_alias is called. None of that really matters for optimizing d_invalidate, but it is part of the background in which d_invalidate lives. All that is significant in d_invalidate is knowing that d_materialise_unique, and possibly d_splice_alias may run concurrently with d_invalidate. It is unlikely and essentially harmless. After my patchset (because I removed all of the d_drop's from .d_revalidate) the only race that should remain is between two parallel calls of d_invalidate. Which probably means we can remove the test for d_unhashed altogether. Right now I just want to make this first big step and make certain the code is solid. After that optimization is easy. Eric -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH 08/11] vfs: Merge check_submounts_and_drop and d_invalidate
On Mon, Feb 24, 2014 at 04:01:29PM -0800, Eric W. Biederman wrote:
> Miklos Szeredi writes:
>
> > On Sat, Feb 15, 2014 at 01:39:22PM -0800, Eric W. Biederman wrote:
> >>
> >> Now that d_invalidate is the only caller of check_submounts_and_drop,
> >> expand check_submounts_and_drop inline in d_invalidate.
> >>
> >> Signed-off-by: "Eric W. Biederman"
> >> ---
> >> fs/dcache.c| 55
> >> +++
> >> include/linux/dcache.h |1 -
> >> 2 files changed, 22 insertions(+), 34 deletions(-)
> >>
> >> diff --git a/fs/dcache.c b/fs/dcache.c
> >> index 27585b1dd6f1..5b41205cbf33 100644
> >> --- a/fs/dcache.c
> >> +++ b/fs/dcache.c
>
> >> -int check_submounts_and_drop(struct dentry *dentry)
> >> +int d_invalidate(struct dentry *dentry)
> >> {
> >>int ret = 0;
> >>
> >> + /*
> >> + * If it's already been dropped, return OK.
> >> + */
> >> + spin_lock(>d_lock);
> >> + if (d_unhashed(dentry)) {
> >> + spin_unlock(>d_lock);
> >> + return 0;
> >> + }
> >> + spin_unlock(>d_lock);
> >> +
> >>/* Negative dentries can be dropped without further checks */
> >>if (!dentry->d_inode) {
> >>d_drop(dentry);
> >
> >
> > You can optimize this by including the negative check within the above
> > d_locked
> > region and calling __d_drop() instead.
>
> For this patch just moving the code and not changing it is the corret
> thing to do because it helps with review and understanding the code.
>
> There are two ways I could see going with optimizing the preamble.
> Simply dropping the d_lock from around the d_unhashed test as a pointer
> dereference should be atomic, and the test is racy against
> d_materialise_unique.
Could you explain? What's the race, and what are the consequences?
--b.
> (We don't always hold the parent
> directories inode mutex when d_invalidate is called). So the d_lock
> buys us very little. Alternatively we could move the work into the
> d_walk callbacks.
>
> That kind of optimization deserves it's own patch that can be reviewed
> independently.
>
> Eric
> --
> To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
> the body of a message to majord...@vger.kernel.org
> More majordomo info at http://vger.kernel.org/majordomo-info.html
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
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More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH 08/11] vfs: Merge check_submounts_and_drop and d_invalidate
On Mon, Feb 24, 2014 at 04:01:29PM -0800, Eric W. Biederman wrote:
Miklos Szeredi mik...@szeredi.hu writes:
On Sat, Feb 15, 2014 at 01:39:22PM -0800, Eric W. Biederman wrote:
Now that d_invalidate is the only caller of check_submounts_and_drop,
expand check_submounts_and_drop inline in d_invalidate.
Signed-off-by: Eric W. Biederman ebied...@xmission.com
---
fs/dcache.c| 55
+++
include/linux/dcache.h |1 -
2 files changed, 22 insertions(+), 34 deletions(-)
diff --git a/fs/dcache.c b/fs/dcache.c
index 27585b1dd6f1..5b41205cbf33 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
-int check_submounts_and_drop(struct dentry *dentry)
+int d_invalidate(struct dentry *dentry)
{
int ret = 0;
+ /*
+ * If it's already been dropped, return OK.
+ */
+ spin_lock(dentry-d_lock);
+ if (d_unhashed(dentry)) {
+ spin_unlock(dentry-d_lock);
+ return 0;
+ }
+ spin_unlock(dentry-d_lock);
+
/* Negative dentries can be dropped without further checks */
if (!dentry-d_inode) {
d_drop(dentry);
You can optimize this by including the negative check within the above
d_locked
region and calling __d_drop() instead.
For this patch just moving the code and not changing it is the corret
thing to do because it helps with review and understanding the code.
There are two ways I could see going with optimizing the preamble.
Simply dropping the d_lock from around the d_unhashed test as a pointer
dereference should be atomic, and the test is racy against
d_materialise_unique.
Could you explain? What's the race, and what are the consequences?
--b.
(We don't always hold the parent
directories inode mutex when d_invalidate is called). So the d_lock
buys us very little. Alternatively we could move the work into the
d_walk callbacks.
That kind of optimization deserves it's own patch that can be reviewed
independently.
Eric
--
To unsubscribe from this list: send the line unsubscribe linux-fsdevel in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
--
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Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH 08/11] vfs: Merge check_submounts_and_drop and d_invalidate
J. Bruce Fields bfie...@fieldses.org writes: On Mon, Feb 24, 2014 at 04:01:29PM -0800, Eric W. Biederman wrote: Miklos Szeredi mik...@szeredi.hu writes: You can optimize this by including the negative check within the above d_locked region and calling __d_drop() instead. For this patch just moving the code and not changing it is the corret thing to do because it helps with review and understanding the code. There are two ways I could see going with optimizing the preamble. Simply dropping the d_lock from around the d_unhashed test as a pointer dereference should be atomic, and the test is racy against d_materialise_unique. Could you explain? What's the race, and what are the consequences? (We don't always hold the parent directories inode mutex when d_invalidate is called). d_unhashed is not a permanent condition because of d_materialise_unique, and d_splice_alias. d_invalidate can be called on an unhashed dentry in one of two ways (either d_revalidate dropped the dentry or another routine that drops the dentry beat the current invocation of d_invalidate to the job). There are 3 places d_revalidate is called. Once on the rcu path with with the appropriate flag set. Once without out the parent i_mutex held, just off of the rcu path, on that path d_invalidate is when d_revalidate fails. Once during lookup with the parent directory i_mutex held. Because the parent direcories i_mutex is not always held accross d_revalidate and the following d_invalidate it happens that d_invalidate is not always an atomic operation. At worst the race results in a dentry that is dropped when it could be hashed, that we will resurrect next time someone attempts to look it up and d_materialise_unique/d_splice_alias is called. None of that really matters for optimizing d_invalidate, but it is part of the background in which d_invalidate lives. All that is significant in d_invalidate is knowing that d_materialise_unique, and possibly d_splice_alias may run concurrently with d_invalidate. It is unlikely and essentially harmless. After my patchset (because I removed all of the d_drop's from .d_revalidate) the only race that should remain is between two parallel calls of d_invalidate. Which probably means we can remove the test for d_unhashed altogether. Right now I just want to make this first big step and make certain the code is solid. After that optimization is easy. Eric -- To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH 08/11] vfs: Merge check_submounts_and_drop and d_invalidate
Miklos Szeredi writes:
> On Sat, Feb 15, 2014 at 01:39:22PM -0800, Eric W. Biederman wrote:
>>
>> Now that d_invalidate is the only caller of check_submounts_and_drop,
>> expand check_submounts_and_drop inline in d_invalidate.
>>
>> Signed-off-by: "Eric W. Biederman"
>> ---
>> fs/dcache.c| 55
>> +++
>> include/linux/dcache.h |1 -
>> 2 files changed, 22 insertions(+), 34 deletions(-)
>>
>> diff --git a/fs/dcache.c b/fs/dcache.c
>> index 27585b1dd6f1..5b41205cbf33 100644
>> --- a/fs/dcache.c
>> +++ b/fs/dcache.c
>> -int check_submounts_and_drop(struct dentry *dentry)
>> +int d_invalidate(struct dentry *dentry)
>> {
>> int ret = 0;
>>
>> +/*
>> + * If it's already been dropped, return OK.
>> + */
>> +spin_lock(>d_lock);
>> +if (d_unhashed(dentry)) {
>> +spin_unlock(>d_lock);
>> +return 0;
>> +}
>> +spin_unlock(>d_lock);
>> +
>> /* Negative dentries can be dropped without further checks */
>> if (!dentry->d_inode) {
>> d_drop(dentry);
>
>
> You can optimize this by including the negative check within the above
> d_locked
> region and calling __d_drop() instead.
For this patch just moving the code and not changing it is the corret
thing to do because it helps with review and understanding the code.
There are two ways I could see going with optimizing the preamble.
Simply dropping the d_lock from around the d_unhashed test as a pointer
dereference should be atomic, and the test is racy against
d_materialise_unique. (We don't always hold the parent
directories inode mutex when d_invalidate is called). So the d_lock
buys us very little. Alternatively we could move the work into the
d_walk callbacks.
That kind of optimization deserves it's own patch that can be reviewed
independently.
Eric
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH 08/11] vfs: Merge check_submounts_and_drop and d_invalidate
Miklos Szeredi mik...@szeredi.hu writes:
On Sat, Feb 15, 2014 at 01:39:22PM -0800, Eric W. Biederman wrote:
Now that d_invalidate is the only caller of check_submounts_and_drop,
expand check_submounts_and_drop inline in d_invalidate.
Signed-off-by: Eric W. Biederman ebied...@xmission.com
---
fs/dcache.c| 55
+++
include/linux/dcache.h |1 -
2 files changed, 22 insertions(+), 34 deletions(-)
diff --git a/fs/dcache.c b/fs/dcache.c
index 27585b1dd6f1..5b41205cbf33 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
-int check_submounts_and_drop(struct dentry *dentry)
+int d_invalidate(struct dentry *dentry)
{
int ret = 0;
+/*
+ * If it's already been dropped, return OK.
+ */
+spin_lock(dentry-d_lock);
+if (d_unhashed(dentry)) {
+spin_unlock(dentry-d_lock);
+return 0;
+}
+spin_unlock(dentry-d_lock);
+
/* Negative dentries can be dropped without further checks */
if (!dentry-d_inode) {
d_drop(dentry);
You can optimize this by including the negative check within the above
d_locked
region and calling __d_drop() instead.
For this patch just moving the code and not changing it is the corret
thing to do because it helps with review and understanding the code.
There are two ways I could see going with optimizing the preamble.
Simply dropping the d_lock from around the d_unhashed test as a pointer
dereference should be atomic, and the test is racy against
d_materialise_unique. (We don't always hold the parent
directories inode mutex when d_invalidate is called). So the d_lock
buys us very little. Alternatively we could move the work into the
d_walk callbacks.
That kind of optimization deserves it's own patch that can be reviewed
independently.
Eric
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Re: [PATCH 08/11] vfs: Merge check_submounts_and_drop and d_invalidate
On Sat, Feb 15, 2014 at 01:39:22PM -0800, Eric W. Biederman wrote:
>
> Now that d_invalidate is the only caller of check_submounts_and_drop,
> expand check_submounts_and_drop inline in d_invalidate.
>
> Signed-off-by: "Eric W. Biederman"
> ---
> fs/dcache.c| 55 +++
> include/linux/dcache.h |1 -
> 2 files changed, 22 insertions(+), 34 deletions(-)
>
> diff --git a/fs/dcache.c b/fs/dcache.c
> index 27585b1dd6f1..5b41205cbf33 100644
> --- a/fs/dcache.c
> +++ b/fs/dcache.c
> @@ -608,32 +608,6 @@ kill_it:
> }
> EXPORT_SYMBOL(dput);
>
> -/**
> - * d_invalidate - invalidate a dentry
> - * @dentry: dentry to invalidate
> - *
> - * Try to invalidate the dentry if it turns out to be
> - * possible. If there are reasons not to delete it
> - * return -EBUSY. On success return 0.
> - *
> - * no dcache lock.
> - */
> -
> -int d_invalidate(struct dentry * dentry)
> -{
> - /*
> - * If it's already been dropped, return OK.
> - */
> - spin_lock(>d_lock);
> - if (d_unhashed(dentry)) {
> - spin_unlock(>d_lock);
> - return 0;
> - }
> - spin_unlock(>d_lock);
> -
> - return check_submounts_and_drop(dentry);
> -}
> -EXPORT_SYMBOL(d_invalidate);
>
> /* This must be called with d_lock held */
> static inline void __dget_dlock(struct dentry *dentry)
> @@ -1175,7 +1149,7 @@ EXPORT_SYMBOL(have_submounts);
> * reachable (e.g. NFS can unhash a directory dentry and then the complete
> * subtree can become unreachable).
> *
> - * Only one of check_submounts_and_drop() and d_set_mounted() must succeed.
> For
> + * Only one of d_invalidate() and d_set_mounted() must succeed. For
> * this reason take rename_lock and d_lock on dentry and ancestors.
> */
> int d_set_mounted(struct dentry *dentry)
> @@ -1184,7 +1158,7 @@ int d_set_mounted(struct dentry *dentry)
> int ret = -ENOENT;
> write_seqlock(_lock);
> for (p = dentry->d_parent; !IS_ROOT(p); p = p->d_parent) {
> - /* Need exclusion wrt. check_submounts_and_drop() */
> + /* Need exclusion wrt. d_invalidate() */
> spin_lock(>d_lock);
> if (unlikely(d_unhashed(p))) {
> spin_unlock(>d_lock);
> @@ -1400,18 +1374,33 @@ static void check_and_drop(void *_data)
> }
>
> /**
> - * check_submounts_and_drop - detach submounts, prune dcache, and drop
> + * d_invalidate - detach submounts, prune dcache, and drop
> + * @dentry: dentry to invalidate (aka detach, prune and drop)
> + *
> + * Try to invalidate the dentry if it turns out to be
> + * possible. If there are reasons not to delete it
> + * return -EBUSY. On success return 0.
> + *
> + * no dcache lock.
> *
> * The final d_drop is done as an atomic operation relative to
> * rename_lock ensuring there are no races with d_set_mounted. This
> * ensures there are no unhashed dentries on the path to a mountpoint.
> - *
> - * @dentry: dentry to detach, prune and drop
> */
> -int check_submounts_and_drop(struct dentry *dentry)
> +int d_invalidate(struct dentry *dentry)
> {
> int ret = 0;
>
> + /*
> + * If it's already been dropped, return OK.
> + */
> + spin_lock(>d_lock);
> + if (d_unhashed(dentry)) {
> + spin_unlock(>d_lock);
> + return 0;
> + }
> + spin_unlock(>d_lock);
> +
> /* Negative dentries can be dropped without further checks */
> if (!dentry->d_inode) {
> d_drop(dentry);
You can optimize this by including the negative check within the above d_locked
region and calling __d_drop() instead.
> @@ -1445,7 +1434,7 @@ int check_submounts_and_drop(struct dentry *dentry)
> out:
> return ret;
> }
> -EXPORT_SYMBOL(check_submounts_and_drop);
> +EXPORT_SYMBOL(d_invalidate);
>
> /**
> * __d_alloc - allocate a dcache entry
> diff --git a/include/linux/dcache.h b/include/linux/dcache.h
> index bf72e9ac6de0..ae77222c3e86 100644
> --- a/include/linux/dcache.h
> +++ b/include/linux/dcache.h
> @@ -265,7 +265,6 @@ extern void d_prune_aliases(struct inode *);
>
> /* test whether we have any submounts in a subdir tree */
> extern int have_submounts(struct dentry *);
> -extern int check_submounts_and_drop(struct dentry *);
>
> /*
> * This adds the entry to the hash queues.
> --
> 1.7.5.4
>
--
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Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH 08/11] vfs: Merge check_submounts_and_drop and d_invalidate
On Sat, Feb 15, 2014 at 01:39:22PM -0800, Eric W. Biederman wrote:
Now that d_invalidate is the only caller of check_submounts_and_drop,
expand check_submounts_and_drop inline in d_invalidate.
Signed-off-by: Eric W. Biederman ebied...@xmission.com
---
fs/dcache.c| 55 +++
include/linux/dcache.h |1 -
2 files changed, 22 insertions(+), 34 deletions(-)
diff --git a/fs/dcache.c b/fs/dcache.c
index 27585b1dd6f1..5b41205cbf33 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -608,32 +608,6 @@ kill_it:
}
EXPORT_SYMBOL(dput);
-/**
- * d_invalidate - invalidate a dentry
- * @dentry: dentry to invalidate
- *
- * Try to invalidate the dentry if it turns out to be
- * possible. If there are reasons not to delete it
- * return -EBUSY. On success return 0.
- *
- * no dcache lock.
- */
-
-int d_invalidate(struct dentry * dentry)
-{
- /*
- * If it's already been dropped, return OK.
- */
- spin_lock(dentry-d_lock);
- if (d_unhashed(dentry)) {
- spin_unlock(dentry-d_lock);
- return 0;
- }
- spin_unlock(dentry-d_lock);
-
- return check_submounts_and_drop(dentry);
-}
-EXPORT_SYMBOL(d_invalidate);
/* This must be called with d_lock held */
static inline void __dget_dlock(struct dentry *dentry)
@@ -1175,7 +1149,7 @@ EXPORT_SYMBOL(have_submounts);
* reachable (e.g. NFS can unhash a directory dentry and then the complete
* subtree can become unreachable).
*
- * Only one of check_submounts_and_drop() and d_set_mounted() must succeed.
For
+ * Only one of d_invalidate() and d_set_mounted() must succeed. For
* this reason take rename_lock and d_lock on dentry and ancestors.
*/
int d_set_mounted(struct dentry *dentry)
@@ -1184,7 +1158,7 @@ int d_set_mounted(struct dentry *dentry)
int ret = -ENOENT;
write_seqlock(rename_lock);
for (p = dentry-d_parent; !IS_ROOT(p); p = p-d_parent) {
- /* Need exclusion wrt. check_submounts_and_drop() */
+ /* Need exclusion wrt. d_invalidate() */
spin_lock(p-d_lock);
if (unlikely(d_unhashed(p))) {
spin_unlock(p-d_lock);
@@ -1400,18 +1374,33 @@ static void check_and_drop(void *_data)
}
/**
- * check_submounts_and_drop - detach submounts, prune dcache, and drop
+ * d_invalidate - detach submounts, prune dcache, and drop
+ * @dentry: dentry to invalidate (aka detach, prune and drop)
+ *
+ * Try to invalidate the dentry if it turns out to be
+ * possible. If there are reasons not to delete it
+ * return -EBUSY. On success return 0.
+ *
+ * no dcache lock.
*
* The final d_drop is done as an atomic operation relative to
* rename_lock ensuring there are no races with d_set_mounted. This
* ensures there are no unhashed dentries on the path to a mountpoint.
- *
- * @dentry: dentry to detach, prune and drop
*/
-int check_submounts_and_drop(struct dentry *dentry)
+int d_invalidate(struct dentry *dentry)
{
int ret = 0;
+ /*
+ * If it's already been dropped, return OK.
+ */
+ spin_lock(dentry-d_lock);
+ if (d_unhashed(dentry)) {
+ spin_unlock(dentry-d_lock);
+ return 0;
+ }
+ spin_unlock(dentry-d_lock);
+
/* Negative dentries can be dropped without further checks */
if (!dentry-d_inode) {
d_drop(dentry);
You can optimize this by including the negative check within the above d_locked
region and calling __d_drop() instead.
@@ -1445,7 +1434,7 @@ int check_submounts_and_drop(struct dentry *dentry)
out:
return ret;
}
-EXPORT_SYMBOL(check_submounts_and_drop);
+EXPORT_SYMBOL(d_invalidate);
/**
* __d_alloc - allocate a dcache entry
diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index bf72e9ac6de0..ae77222c3e86 100644
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -265,7 +265,6 @@ extern void d_prune_aliases(struct inode *);
/* test whether we have any submounts in a subdir tree */
extern int have_submounts(struct dentry *);
-extern int check_submounts_and_drop(struct dentry *);
/*
* This adds the entry to the hash queues.
--
1.7.5.4
--
To unsubscribe from this list: send the line unsubscribe linux-kernel in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[PATCH 08/11] vfs: Merge check_submounts_and_drop and d_invalidate
Now that d_invalidate is the only caller of check_submounts_and_drop,
expand check_submounts_and_drop inline in d_invalidate.
Signed-off-by: "Eric W. Biederman"
---
fs/dcache.c| 55 +++
include/linux/dcache.h |1 -
2 files changed, 22 insertions(+), 34 deletions(-)
diff --git a/fs/dcache.c b/fs/dcache.c
index 27585b1dd6f1..5b41205cbf33 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -608,32 +608,6 @@ kill_it:
}
EXPORT_SYMBOL(dput);
-/**
- * d_invalidate - invalidate a dentry
- * @dentry: dentry to invalidate
- *
- * Try to invalidate the dentry if it turns out to be
- * possible. If there are reasons not to delete it
- * return -EBUSY. On success return 0.
- *
- * no dcache lock.
- */
-
-int d_invalidate(struct dentry * dentry)
-{
- /*
-* If it's already been dropped, return OK.
-*/
- spin_lock(>d_lock);
- if (d_unhashed(dentry)) {
- spin_unlock(>d_lock);
- return 0;
- }
- spin_unlock(>d_lock);
-
- return check_submounts_and_drop(dentry);
-}
-EXPORT_SYMBOL(d_invalidate);
/* This must be called with d_lock held */
static inline void __dget_dlock(struct dentry *dentry)
@@ -1175,7 +1149,7 @@ EXPORT_SYMBOL(have_submounts);
* reachable (e.g. NFS can unhash a directory dentry and then the complete
* subtree can become unreachable).
*
- * Only one of check_submounts_and_drop() and d_set_mounted() must succeed.
For
+ * Only one of d_invalidate() and d_set_mounted() must succeed. For
* this reason take rename_lock and d_lock on dentry and ancestors.
*/
int d_set_mounted(struct dentry *dentry)
@@ -1184,7 +1158,7 @@ int d_set_mounted(struct dentry *dentry)
int ret = -ENOENT;
write_seqlock(_lock);
for (p = dentry->d_parent; !IS_ROOT(p); p = p->d_parent) {
- /* Need exclusion wrt. check_submounts_and_drop() */
+ /* Need exclusion wrt. d_invalidate() */
spin_lock(>d_lock);
if (unlikely(d_unhashed(p))) {
spin_unlock(>d_lock);
@@ -1400,18 +1374,33 @@ static void check_and_drop(void *_data)
}
/**
- * check_submounts_and_drop - detach submounts, prune dcache, and drop
+ * d_invalidate - detach submounts, prune dcache, and drop
+ * @dentry: dentry to invalidate (aka detach, prune and drop)
+ *
+ * Try to invalidate the dentry if it turns out to be
+ * possible. If there are reasons not to delete it
+ * return -EBUSY. On success return 0.
+ *
+ * no dcache lock.
*
* The final d_drop is done as an atomic operation relative to
* rename_lock ensuring there are no races with d_set_mounted. This
* ensures there are no unhashed dentries on the path to a mountpoint.
- *
- * @dentry: dentry to detach, prune and drop
*/
-int check_submounts_and_drop(struct dentry *dentry)
+int d_invalidate(struct dentry *dentry)
{
int ret = 0;
+ /*
+* If it's already been dropped, return OK.
+*/
+ spin_lock(>d_lock);
+ if (d_unhashed(dentry)) {
+ spin_unlock(>d_lock);
+ return 0;
+ }
+ spin_unlock(>d_lock);
+
/* Negative dentries can be dropped without further checks */
if (!dentry->d_inode) {
d_drop(dentry);
@@ -1445,7 +1434,7 @@ int check_submounts_and_drop(struct dentry *dentry)
out:
return ret;
}
-EXPORT_SYMBOL(check_submounts_and_drop);
+EXPORT_SYMBOL(d_invalidate);
/**
* __d_alloc - allocate a dcache entry
diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index bf72e9ac6de0..ae77222c3e86 100644
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -265,7 +265,6 @@ extern void d_prune_aliases(struct inode *);
/* test whether we have any submounts in a subdir tree */
extern int have_submounts(struct dentry *);
-extern int check_submounts_and_drop(struct dentry *);
/*
* This adds the entry to the hash queues.
--
1.7.5.4
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
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More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[PATCH 08/11] vfs: Merge check_submounts_and_drop and d_invalidate
Now that d_invalidate is the only caller of check_submounts_and_drop,
expand check_submounts_and_drop inline in d_invalidate.
Signed-off-by: Eric W. Biederman ebied...@xmission.com
---
fs/dcache.c| 55 +++
include/linux/dcache.h |1 -
2 files changed, 22 insertions(+), 34 deletions(-)
diff --git a/fs/dcache.c b/fs/dcache.c
index 27585b1dd6f1..5b41205cbf33 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -608,32 +608,6 @@ kill_it:
}
EXPORT_SYMBOL(dput);
-/**
- * d_invalidate - invalidate a dentry
- * @dentry: dentry to invalidate
- *
- * Try to invalidate the dentry if it turns out to be
- * possible. If there are reasons not to delete it
- * return -EBUSY. On success return 0.
- *
- * no dcache lock.
- */
-
-int d_invalidate(struct dentry * dentry)
-{
- /*
-* If it's already been dropped, return OK.
-*/
- spin_lock(dentry-d_lock);
- if (d_unhashed(dentry)) {
- spin_unlock(dentry-d_lock);
- return 0;
- }
- spin_unlock(dentry-d_lock);
-
- return check_submounts_and_drop(dentry);
-}
-EXPORT_SYMBOL(d_invalidate);
/* This must be called with d_lock held */
static inline void __dget_dlock(struct dentry *dentry)
@@ -1175,7 +1149,7 @@ EXPORT_SYMBOL(have_submounts);
* reachable (e.g. NFS can unhash a directory dentry and then the complete
* subtree can become unreachable).
*
- * Only one of check_submounts_and_drop() and d_set_mounted() must succeed.
For
+ * Only one of d_invalidate() and d_set_mounted() must succeed. For
* this reason take rename_lock and d_lock on dentry and ancestors.
*/
int d_set_mounted(struct dentry *dentry)
@@ -1184,7 +1158,7 @@ int d_set_mounted(struct dentry *dentry)
int ret = -ENOENT;
write_seqlock(rename_lock);
for (p = dentry-d_parent; !IS_ROOT(p); p = p-d_parent) {
- /* Need exclusion wrt. check_submounts_and_drop() */
+ /* Need exclusion wrt. d_invalidate() */
spin_lock(p-d_lock);
if (unlikely(d_unhashed(p))) {
spin_unlock(p-d_lock);
@@ -1400,18 +1374,33 @@ static void check_and_drop(void *_data)
}
/**
- * check_submounts_and_drop - detach submounts, prune dcache, and drop
+ * d_invalidate - detach submounts, prune dcache, and drop
+ * @dentry: dentry to invalidate (aka detach, prune and drop)
+ *
+ * Try to invalidate the dentry if it turns out to be
+ * possible. If there are reasons not to delete it
+ * return -EBUSY. On success return 0.
+ *
+ * no dcache lock.
*
* The final d_drop is done as an atomic operation relative to
* rename_lock ensuring there are no races with d_set_mounted. This
* ensures there are no unhashed dentries on the path to a mountpoint.
- *
- * @dentry: dentry to detach, prune and drop
*/
-int check_submounts_and_drop(struct dentry *dentry)
+int d_invalidate(struct dentry *dentry)
{
int ret = 0;
+ /*
+* If it's already been dropped, return OK.
+*/
+ spin_lock(dentry-d_lock);
+ if (d_unhashed(dentry)) {
+ spin_unlock(dentry-d_lock);
+ return 0;
+ }
+ spin_unlock(dentry-d_lock);
+
/* Negative dentries can be dropped without further checks */
if (!dentry-d_inode) {
d_drop(dentry);
@@ -1445,7 +1434,7 @@ int check_submounts_and_drop(struct dentry *dentry)
out:
return ret;
}
-EXPORT_SYMBOL(check_submounts_and_drop);
+EXPORT_SYMBOL(d_invalidate);
/**
* __d_alloc - allocate a dcache entry
diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index bf72e9ac6de0..ae77222c3e86 100644
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -265,7 +265,6 @@ extern void d_prune_aliases(struct inode *);
/* test whether we have any submounts in a subdir tree */
extern int have_submounts(struct dentry *);
-extern int check_submounts_and_drop(struct dentry *);
/*
* This adds the entry to the hash queues.
--
1.7.5.4
--
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the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
