Re: [PATCH] vfs, syncfs: Do not ignore return code from ->sync_fs()
On Wed, Dec 16, 2020 at 10:53:16AM -0500, Jeff Layton wrote:
> On Wed, 2020-12-16 at 10:44 -0500, Jeff Layton wrote:
> > On Wed, 2020-12-16 at 10:14 -0500, Vivek Goyal wrote:
> > > On Wed, Dec 16, 2020 at 09:57:49AM -0500, Jeff Layton wrote:
> > > > On Wed, 2020-12-16 at 09:38 -0500, Vivek Goyal wrote:
> > > > > I see that current implementation of __sync_filesystem() ignores the
> > > > > return code from ->sync_fs(). I am not sure why that's the case.
> > > > >
> > > > > Ignoring ->sync_fs() return code is problematic for overlayfs where
> > > > > it can return error if sync_filesystem() on upper super block failed.
> > > > > That error will simply be lost and sycnfs(overlay_fd), will get
> > > > > success (despite the fact it failed).
> > > > >
> > > > > I am assuming that we want to continue to call __sync_blockdev()
> > > > > despite the fact that there have been errors reported from
> > > > > ->sync_fs(). So I wrote this simple patch which captures the
> > > > > error from ->sync_fs() but continues to call __sync_blockdev()
> > > > > and returns error from sync_fs() if there is one.
> > > > >
> > > > > There might be some very good reasons to not capture ->sync_fs()
> > > > > return code, I don't know. Hence thought of proposing this patch.
> > > > > Atleast I will get to know the reason. I still need to figure
> > > > > a way out how to propagate overlay sync_fs() errors to user
> > > > > space.
> > > > >
> > > > > Signed-off-by: Vivek Goyal
> > > > > ---
> > > > > fs/sync.c |8 ++--
> > > > > 1 file changed, 6 insertions(+), 2 deletions(-)
> > > > >
> > > > > Index: redhat-linux/fs/sync.c
> > > > > ===
> > > > > --- redhat-linux.orig/fs/sync.c 2020-12-16 09:15:49.831565653
> > > > > -0500
> > > > > +++ redhat-linux/fs/sync.c2020-12-16 09:23:42.499853207 -0500
> > > > > @@ -30,14 +30,18 @@
> > > > > */
> > > > > static int __sync_filesystem(struct super_block *sb, int wait)
> > > > > {
> > > > > + int ret, ret2;
> > > > > +
> > > > > if (wait)
> > > > > sync_inodes_sb(sb);
> > > > > else
> > > > > writeback_inodes_sb(sb, WB_REASON_SYNC);
> > > > >
> > > > >
> > > > > if (sb->s_op->sync_fs)
> > > > > - sb->s_op->sync_fs(sb, wait);
> > > > > - return __sync_blockdev(sb->s_bdev, wait);
> > > > > + ret = sb->s_op->sync_fs(sb, wait);
> > > > > + ret2 = __sync_blockdev(sb->s_bdev, wait);
> > > > > +
> > > > > + return ret ? ret : ret2;
> > > > > }
> > > > >
> > > > >
> > > > > /*
> > > > >
> > > >
> > > > I posted a patchset that took a similar approach a couple of years ago,
> > > > and we decided not to go with it [1].
> > > >
> > > > While it's not ideal to ignore the error here, I think this is likely to
> > > > break stuff.
> > >
> > > So one side affect I see is that syncfs() might start returning errors
> > > in some cases which were not reported at all. I am wondering will that
> > > count as breakage.
> > >
> > > > What may be better is to just make sync_fs void return, so
> > > > people don't think that returned errors there mean anything.
> > >
> > > May be.
> > >
> > > But then question remains that how do we return error to user space
> > > in syncfs(fd) for overlayfs. I will not be surprised if other
> > > filesystems want to return errors as well.
> > >
> > > Shall I create new helpers and call these in case of syncfs(). But
> > > that too will start returning new errors on syncfs(). So it does
> > > not solve that problem (if it is a problem).
> > >
> > > Or we can define a new super block op say ->sync_fs2() and call that
> > > first and in that case capture return code. That way it will not
> > > impact existing cases and overlayfs can possibly make use of
> > > ->sync_fs2() and return error. IOW, impact will be limited to
> > > only file systems which chose to implement ->sync_fs2().
> > >
> > > Thanks
> > > Vivek
> > >
> >
> > Sure, it's possible to add a sb->sync_fs2, but the problem is that
> > sync_fs is a superblock op, and is missing a lot of important context
> > about how it got called.
> >
> > syncfs(2) syscall takes a file descriptor argument. I'd add a new f_op-
> > > syncfs vector and turn most of the current guts of the syncfs syscall
> > into a generic_syncfs() that gets called when f_op->syncfs isn't
> > defined.
> >
> > Overlayfs could then add a ->syncfs op that would give it control over
> > what error gets returned. With that, you could basically leave the old
> > sb->sync_fs routine alone.
> >
> > I think that's probably the safest approach for allowing overlayfs to
> > propagate syncfs errors from the upper layer to the overlay.
> >
>
> To be clear, I mean something like this (draft, untested) patch. You'd
> also need to add a new ->syncfs op for overlayfs, and that could just do
> a check_and_advance against the upper layer sb's errseq_t after calling
> sync_file
Re: [PATCH] vfs, syncfs: Do not ignore return code from ->sync_fs()
On Wed, 2020-12-16 at 10:44 -0500, Jeff Layton wrote:
> On Wed, 2020-12-16 at 10:14 -0500, Vivek Goyal wrote:
> > On Wed, Dec 16, 2020 at 09:57:49AM -0500, Jeff Layton wrote:
> > > On Wed, 2020-12-16 at 09:38 -0500, Vivek Goyal wrote:
> > > > I see that current implementation of __sync_filesystem() ignores the
> > > > return code from ->sync_fs(). I am not sure why that's the case.
> > > >
> > > > Ignoring ->sync_fs() return code is problematic for overlayfs where
> > > > it can return error if sync_filesystem() on upper super block failed.
> > > > That error will simply be lost and sycnfs(overlay_fd), will get
> > > > success (despite the fact it failed).
> > > >
> > > > I am assuming that we want to continue to call __sync_blockdev()
> > > > despite the fact that there have been errors reported from
> > > > ->sync_fs(). So I wrote this simple patch which captures the
> > > > error from ->sync_fs() but continues to call __sync_blockdev()
> > > > and returns error from sync_fs() if there is one.
> > > >
> > > > There might be some very good reasons to not capture ->sync_fs()
> > > > return code, I don't know. Hence thought of proposing this patch.
> > > > Atleast I will get to know the reason. I still need to figure
> > > > a way out how to propagate overlay sync_fs() errors to user
> > > > space.
> > > >
> > > > Signed-off-by: Vivek Goyal
> > > > ---
> > > > fs/sync.c |8 ++--
> > > > 1 file changed, 6 insertions(+), 2 deletions(-)
> > > >
> > > > Index: redhat-linux/fs/sync.c
> > > > ===
> > > > --- redhat-linux.orig/fs/sync.c 2020-12-16 09:15:49.831565653 -0500
> > > > +++ redhat-linux/fs/sync.c 2020-12-16 09:23:42.499853207 -0500
> > > > @@ -30,14 +30,18 @@
> > > > */
> > > > static int __sync_filesystem(struct super_block *sb, int wait)
> > > > {
> > > > + int ret, ret2;
> > > > +
> > > > if (wait)
> > > > sync_inodes_sb(sb);
> > > > else
> > > > writeback_inodes_sb(sb, WB_REASON_SYNC);
> > > >
> > > >
> > > > if (sb->s_op->sync_fs)
> > > > - sb->s_op->sync_fs(sb, wait);
> > > > - return __sync_blockdev(sb->s_bdev, wait);
> > > > + ret = sb->s_op->sync_fs(sb, wait);
> > > > + ret2 = __sync_blockdev(sb->s_bdev, wait);
> > > > +
> > > > + return ret ? ret : ret2;
> > > > }
> > > >
> > > >
> > > > /*
> > > >
> > >
> > > I posted a patchset that took a similar approach a couple of years ago,
> > > and we decided not to go with it [1].
> > >
> > > While it's not ideal to ignore the error here, I think this is likely to
> > > break stuff.
> >
> > So one side affect I see is that syncfs() might start returning errors
> > in some cases which were not reported at all. I am wondering will that
> > count as breakage.
> >
> > > What may be better is to just make sync_fs void return, so
> > > people don't think that returned errors there mean anything.
> >
> > May be.
> >
> > But then question remains that how do we return error to user space
> > in syncfs(fd) for overlayfs. I will not be surprised if other
> > filesystems want to return errors as well.
> >
> > Shall I create new helpers and call these in case of syncfs(). But
> > that too will start returning new errors on syncfs(). So it does
> > not solve that problem (if it is a problem).
> >
> > Or we can define a new super block op say ->sync_fs2() and call that
> > first and in that case capture return code. That way it will not
> > impact existing cases and overlayfs can possibly make use of
> > ->sync_fs2() and return error. IOW, impact will be limited to
> > only file systems which chose to implement ->sync_fs2().
> >
> > Thanks
> > Vivek
> >
>
> Sure, it's possible to add a sb->sync_fs2, but the problem is that
> sync_fs is a superblock op, and is missing a lot of important context
> about how it got called.
>
> syncfs(2) syscall takes a file descriptor argument. I'd add a new f_op-
> > syncfs vector and turn most of the current guts of the syncfs syscall
> into a generic_syncfs() that gets called when f_op->syncfs isn't
> defined.
>
> Overlayfs could then add a ->syncfs op that would give it control over
> what error gets returned. With that, you could basically leave the old
> sb->sync_fs routine alone.
>
> I think that's probably the safest approach for allowing overlayfs to
> propagate syncfs errors from the upper layer to the overlay.
>
To be clear, I mean something like this (draft, untested) patch. You'd
also need to add a new ->syncfs op for overlayfs, and that could just do
a check_and_advance against the upper layer sb's errseq_t after calling
sync_filesystem.
---8<-
[PATCH] vfs: add new f_op->syncfs vector
Signed-off-by: Jeff Layton
---
fs/sync.c | 30 +-
include/linux/fs.h | 1 +
2 files changed, 22 insertions(+), 9 deletions(-)
diff --g
Re: [PATCH] vfs, syncfs: Do not ignore return code from ->sync_fs()
On Wed, 2020-12-16 at 10:14 -0500, Vivek Goyal wrote:
> On Wed, Dec 16, 2020 at 09:57:49AM -0500, Jeff Layton wrote:
> > On Wed, 2020-12-16 at 09:38 -0500, Vivek Goyal wrote:
> > > I see that current implementation of __sync_filesystem() ignores the
> > > return code from ->sync_fs(). I am not sure why that's the case.
> > >
> > > Ignoring ->sync_fs() return code is problematic for overlayfs where
> > > it can return error if sync_filesystem() on upper super block failed.
> > > That error will simply be lost and sycnfs(overlay_fd), will get
> > > success (despite the fact it failed).
> > >
> > > I am assuming that we want to continue to call __sync_blockdev()
> > > despite the fact that there have been errors reported from
> > > ->sync_fs(). So I wrote this simple patch which captures the
> > > error from ->sync_fs() but continues to call __sync_blockdev()
> > > and returns error from sync_fs() if there is one.
> > >
> > > There might be some very good reasons to not capture ->sync_fs()
> > > return code, I don't know. Hence thought of proposing this patch.
> > > Atleast I will get to know the reason. I still need to figure
> > > a way out how to propagate overlay sync_fs() errors to user
> > > space.
> > >
> > > Signed-off-by: Vivek Goyal
> > > ---
> > > fs/sync.c |8 ++--
> > > 1 file changed, 6 insertions(+), 2 deletions(-)
> > >
> > > Index: redhat-linux/fs/sync.c
> > > ===
> > > --- redhat-linux.orig/fs/sync.c 2020-12-16 09:15:49.831565653 -0500
> > > +++ redhat-linux/fs/sync.c2020-12-16 09:23:42.499853207 -0500
> > > @@ -30,14 +30,18 @@
> > > */
> > > static int __sync_filesystem(struct super_block *sb, int wait)
> > > {
> > > + int ret, ret2;
> > > +
> > > if (wait)
> > > sync_inodes_sb(sb);
> > > else
> > > writeback_inodes_sb(sb, WB_REASON_SYNC);
> > >
> > >
> > > if (sb->s_op->sync_fs)
> > > - sb->s_op->sync_fs(sb, wait);
> > > - return __sync_blockdev(sb->s_bdev, wait);
> > > + ret = sb->s_op->sync_fs(sb, wait);
> > > + ret2 = __sync_blockdev(sb->s_bdev, wait);
> > > +
> > > + return ret ? ret : ret2;
> > > }
> > >
> > >
> > > /*
> > >
> >
> > I posted a patchset that took a similar approach a couple of years ago,
> > and we decided not to go with it [1].
> >
> > While it's not ideal to ignore the error here, I think this is likely to
> > break stuff.
>
> So one side affect I see is that syncfs() might start returning errors
> in some cases which were not reported at all. I am wondering will that
> count as breakage.
>
> > What may be better is to just make sync_fs void return, so
> > people don't think that returned errors there mean anything.
>
> May be.
>
> But then question remains that how do we return error to user space
> in syncfs(fd) for overlayfs. I will not be surprised if other
> filesystems want to return errors as well.
>
> Shall I create new helpers and call these in case of syncfs(). But
> that too will start returning new errors on syncfs(). So it does
> not solve that problem (if it is a problem).
>
> Or we can define a new super block op say ->sync_fs2() and call that
> first and in that case capture return code. That way it will not
> impact existing cases and overlayfs can possibly make use of
> ->sync_fs2() and return error. IOW, impact will be limited to
> only file systems which chose to implement ->sync_fs2().
>
> Thanks
> Vivek
>
Sure, it's possible to add a sb->sync_fs2, but the problem is that
sync_fs is a superblock op, and is missing a lot of important context
about how it got called.
syncfs(2) syscall takes a file descriptor argument. I'd add a new f_op-
>syncfs vector and turn most of the current guts of the syncfs syscall
into a generic_syncfs() that gets called when f_op->syncfs isn't
defined.
Overlayfs could then add a ->syncfs op that would give it control over
what error gets returned. With that, you could basically leave the old
sb->sync_fs routine alone.
I think that's probably the safest approach for allowing overlayfs to
propagate syncfs errors from the upper layer to the overlay.
--
Jeff Layton
Re: [PATCH] vfs, syncfs: Do not ignore return code from ->sync_fs()
On Wed, Dec 16, 2020 at 09:57:49AM -0500, Jeff Layton wrote:
> On Wed, 2020-12-16 at 09:38 -0500, Vivek Goyal wrote:
> > I see that current implementation of __sync_filesystem() ignores the
> > return code from ->sync_fs(). I am not sure why that's the case.
> >
> > Ignoring ->sync_fs() return code is problematic for overlayfs where
> > it can return error if sync_filesystem() on upper super block failed.
> > That error will simply be lost and sycnfs(overlay_fd), will get
> > success (despite the fact it failed).
> >
> > I am assuming that we want to continue to call __sync_blockdev()
> > despite the fact that there have been errors reported from
> > ->sync_fs(). So I wrote this simple patch which captures the
> > error from ->sync_fs() but continues to call __sync_blockdev()
> > and returns error from sync_fs() if there is one.
> >
> > There might be some very good reasons to not capture ->sync_fs()
> > return code, I don't know. Hence thought of proposing this patch.
> > Atleast I will get to know the reason. I still need to figure
> > a way out how to propagate overlay sync_fs() errors to user
> > space.
> >
> > Signed-off-by: Vivek Goyal
> > ---
> > fs/sync.c |8 ++--
> > 1 file changed, 6 insertions(+), 2 deletions(-)
> >
> > Index: redhat-linux/fs/sync.c
> > ===
> > --- redhat-linux.orig/fs/sync.c 2020-12-16 09:15:49.831565653 -0500
> > +++ redhat-linux/fs/sync.c 2020-12-16 09:23:42.499853207 -0500
> > @@ -30,14 +30,18 @@
> > */
> > static int __sync_filesystem(struct super_block *sb, int wait)
> > {
> > + int ret, ret2;
> > +
> > if (wait)
> > sync_inodes_sb(sb);
> > else
> > writeback_inodes_sb(sb, WB_REASON_SYNC);
> >
> >
> > if (sb->s_op->sync_fs)
> > - sb->s_op->sync_fs(sb, wait);
> > - return __sync_blockdev(sb->s_bdev, wait);
> > + ret = sb->s_op->sync_fs(sb, wait);
> > + ret2 = __sync_blockdev(sb->s_bdev, wait);
> > +
> > + return ret ? ret : ret2;
> > }
> >
> >
> > /*
> >
>
> I posted a patchset that took a similar approach a couple of years ago,
> and we decided not to go with it [1].
>
> While it's not ideal to ignore the error here, I think this is likely to
> break stuff.
So one side affect I see is that syncfs() might start returning errors
in some cases which were not reported at all. I am wondering will that
count as breakage.
> What may be better is to just make sync_fs void return, so
> people don't think that returned errors there mean anything.
May be.
But then question remains that how do we return error to user space
in syncfs(fd) for overlayfs. I will not be surprised if other
filesystems want to return errors as well.
Shall I create new helpers and call these in case of syncfs(). But
that too will start returning new errors on syncfs(). So it does
not solve that problem (if it is a problem).
Or we can define a new super block op say ->sync_fs2() and call that
first and in that case capture return code. That way it will not
impact existing cases and overlayfs can possibly make use of
->sync_fs2() and return error. IOW, impact will be limited to
only file systems which chose to implement ->sync_fs2().
Thanks
Vivek
>
> [1]:
> https://lore.kernel.org/linux-fsdevel/20180518123415.28181-1-jlay...@kernel.org/
> --
> Jeff Layton
>
Re: [PATCH] vfs, syncfs: Do not ignore return code from ->sync_fs()
On Wed, 2020-12-16 at 09:38 -0500, Vivek Goyal wrote:
> I see that current implementation of __sync_filesystem() ignores the
> return code from ->sync_fs(). I am not sure why that's the case.
>
> Ignoring ->sync_fs() return code is problematic for overlayfs where
> it can return error if sync_filesystem() on upper super block failed.
> That error will simply be lost and sycnfs(overlay_fd), will get
> success (despite the fact it failed).
>
> I am assuming that we want to continue to call __sync_blockdev()
> despite the fact that there have been errors reported from
> ->sync_fs(). So I wrote this simple patch which captures the
> error from ->sync_fs() but continues to call __sync_blockdev()
> and returns error from sync_fs() if there is one.
>
> There might be some very good reasons to not capture ->sync_fs()
> return code, I don't know. Hence thought of proposing this patch.
> Atleast I will get to know the reason. I still need to figure
> a way out how to propagate overlay sync_fs() errors to user
> space.
>
> Signed-off-by: Vivek Goyal
> ---
> fs/sync.c |8 ++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
> Index: redhat-linux/fs/sync.c
> ===
> --- redhat-linux.orig/fs/sync.c 2020-12-16 09:15:49.831565653 -0500
> +++ redhat-linux/fs/sync.c2020-12-16 09:23:42.499853207 -0500
> @@ -30,14 +30,18 @@
> */
> static int __sync_filesystem(struct super_block *sb, int wait)
> {
> + int ret, ret2;
> +
> if (wait)
> sync_inodes_sb(sb);
> else
> writeback_inodes_sb(sb, WB_REASON_SYNC);
>
>
> if (sb->s_op->sync_fs)
> - sb->s_op->sync_fs(sb, wait);
> - return __sync_blockdev(sb->s_bdev, wait);
> + ret = sb->s_op->sync_fs(sb, wait);
> + ret2 = __sync_blockdev(sb->s_bdev, wait);
> +
> + return ret ? ret : ret2;
> }
>
>
> /*
>
I posted a patchset that took a similar approach a couple of years ago,
and we decided not to go with it [1].
While it's not ideal to ignore the error here, I think this is likely to
break stuff. What may be better is to just make sync_fs void return, so
people don't think that returned errors there mean anything.
[1]:
https://lore.kernel.org/linux-fsdevel/20180518123415.28181-1-jlay...@kernel.org/
--
Jeff Layton
[PATCH] vfs, syncfs: Do not ignore return code from ->sync_fs()
I see that current implementation of __sync_filesystem() ignores the
return code from ->sync_fs(). I am not sure why that's the case.
Ignoring ->sync_fs() return code is problematic for overlayfs where
it can return error if sync_filesystem() on upper super block failed.
That error will simply be lost and sycnfs(overlay_fd), will get
success (despite the fact it failed).
I am assuming that we want to continue to call __sync_blockdev()
despite the fact that there have been errors reported from
->sync_fs(). So I wrote this simple patch which captures the
error from ->sync_fs() but continues to call __sync_blockdev()
and returns error from sync_fs() if there is one.
There might be some very good reasons to not capture ->sync_fs()
return code, I don't know. Hence thought of proposing this patch.
Atleast I will get to know the reason. I still need to figure
a way out how to propagate overlay sync_fs() errors to user
space.
Signed-off-by: Vivek Goyal
---
fs/sync.c |8 ++--
1 file changed, 6 insertions(+), 2 deletions(-)
Index: redhat-linux/fs/sync.c
===
--- redhat-linux.orig/fs/sync.c 2020-12-16 09:15:49.831565653 -0500
+++ redhat-linux/fs/sync.c 2020-12-16 09:23:42.499853207 -0500
@@ -30,14 +30,18 @@
*/
static int __sync_filesystem(struct super_block *sb, int wait)
{
+ int ret, ret2;
+
if (wait)
sync_inodes_sb(sb);
else
writeback_inodes_sb(sb, WB_REASON_SYNC);
if (sb->s_op->sync_fs)
- sb->s_op->sync_fs(sb, wait);
- return __sync_blockdev(sb->s_bdev, wait);
+ ret = sb->s_op->sync_fs(sb, wait);
+ ret2 = __sync_blockdev(sb->s_bdev, wait);
+
+ return ret ? ret : ret2;
}
/*
