Re: [RFC PATCH] Re: Repeated fork() causes SLAB to grow without bound
On Tue, Jun 04, 2013 at 06:37:25AM -0400, Rik van Riel wrote: > On 06/03/2013 03:50 PM, Daniel Forrest wrote: > > On Tue, Aug 21, 2012 at 11:29:54PM -0400, Rik van Riel wrote: > >> On 08/21/2012 11:20 PM, Michel Lespinasse wrote: > >>> On Mon, Aug 20, 2012 at 02:39:26AM -0700, Michel Lespinasse wrote: > Instead of adding an atomic count for page references, we could limit > the anon_vma stacking depth. In fork, we would only clone anon_vmas > that have a low enough generation count. I think that's not great > (adds a special case for the deep-fork-without-exec behavior), but > still better than the atomic page reference counter. > >>> > >>> Here is an attached patch to demonstrate the idea. > >>> > >>> anon_vma_clone() is modified to return the length of the existing same_vma > >>> anon vma chain, and we create a new anon_vma in the child only on the > >>> first > >>> fork (this could be tweaked to allow up to a set number of forks, but > >>> I think the first fork would cover all the common forking server cases). > >> > >> I suspect we need 2 or 3. > >> > >> Some forking servers first fork off one child, and have > >> the original parent exit, in order to "background the server". > >> That first child then becomes the parent to the real child > >> processes that do the work. > >> > >> It is conceivable that we might need an extra level for > >> processes that do something special with privilege dropping, > >> namespace changing, etc... > >> > >> Even setting the threshold to 5 should be totally harmless, > >> since the problem does not kick in until we have really > >> long chains, like in Dan's bug report. > > > > I have been running with Michel's patch (with the threshold set to 5) > > for quite a few months now and can confirm that it does indeed solve > > my problem. I am not a kernel developer, so I would appreciate if one > > of you could push this into the kernel tree. > > > > NOTE: I have attached Michel's patch with "(length > 1)" modified to > > "(length > 5)" and added a "Tested-by:". > > Thank you for testing this. > > I believe this code should go into the Linux kernel, > since it closes up what could be a denial of service > attack (albeit a local one) with the anonvma code. Agreed. The only thing I don't like about this patch is the hardcoding of number 5: could we make it a variable to tweak with sysfs/sysctl so if some weird workload arises we have a tuning tweak? It'd cost one cacheline during fork, so it doesn't look excessive overhead. Thanks, Andrea -- 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: [RFC PATCH] Re: Repeated fork() causes SLAB to grow without bound
On Tue, Jun 04, 2013 at 06:37:25AM -0400, Rik van Riel wrote: On 06/03/2013 03:50 PM, Daniel Forrest wrote: On Tue, Aug 21, 2012 at 11:29:54PM -0400, Rik van Riel wrote: On 08/21/2012 11:20 PM, Michel Lespinasse wrote: On Mon, Aug 20, 2012 at 02:39:26AM -0700, Michel Lespinasse wrote: Instead of adding an atomic count for page references, we could limit the anon_vma stacking depth. In fork, we would only clone anon_vmas that have a low enough generation count. I think that's not great (adds a special case for the deep-fork-without-exec behavior), but still better than the atomic page reference counter. Here is an attached patch to demonstrate the idea. anon_vma_clone() is modified to return the length of the existing same_vma anon vma chain, and we create a new anon_vma in the child only on the first fork (this could be tweaked to allow up to a set number of forks, but I think the first fork would cover all the common forking server cases). I suspect we need 2 or 3. Some forking servers first fork off one child, and have the original parent exit, in order to background the server. That first child then becomes the parent to the real child processes that do the work. It is conceivable that we might need an extra level for processes that do something special with privilege dropping, namespace changing, etc... Even setting the threshold to 5 should be totally harmless, since the problem does not kick in until we have really long chains, like in Dan's bug report. I have been running with Michel's patch (with the threshold set to 5) for quite a few months now and can confirm that it does indeed solve my problem. I am not a kernel developer, so I would appreciate if one of you could push this into the kernel tree. NOTE: I have attached Michel's patch with (length 1) modified to (length 5) and added a Tested-by:. Thank you for testing this. I believe this code should go into the Linux kernel, since it closes up what could be a denial of service attack (albeit a local one) with the anonvma code. Agreed. The only thing I don't like about this patch is the hardcoding of number 5: could we make it a variable to tweak with sysfs/sysctl so if some weird workload arises we have a tuning tweak? It'd cost one cacheline during fork, so it doesn't look excessive overhead. Thanks, Andrea -- 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: [RFC PATCH] Re: Repeated fork() causes SLAB to grow without bound
On 06/03/2013 03:50 PM, Daniel Forrest wrote: On Tue, Aug 21, 2012 at 11:29:54PM -0400, Rik van Riel wrote: On 08/21/2012 11:20 PM, Michel Lespinasse wrote: On Mon, Aug 20, 2012 at 02:39:26AM -0700, Michel Lespinasse wrote: Instead of adding an atomic count for page references, we could limit the anon_vma stacking depth. In fork, we would only clone anon_vmas that have a low enough generation count. I think that's not great (adds a special case for the deep-fork-without-exec behavior), but still better than the atomic page reference counter. Here is an attached patch to demonstrate the idea. anon_vma_clone() is modified to return the length of the existing same_vma anon vma chain, and we create a new anon_vma in the child only on the first fork (this could be tweaked to allow up to a set number of forks, but I think the first fork would cover all the common forking server cases). I suspect we need 2 or 3. Some forking servers first fork off one child, and have the original parent exit, in order to "background the server". That first child then becomes the parent to the real child processes that do the work. It is conceivable that we might need an extra level for processes that do something special with privilege dropping, namespace changing, etc... Even setting the threshold to 5 should be totally harmless, since the problem does not kick in until we have really long chains, like in Dan's bug report. I have been running with Michel's patch (with the threshold set to 5) for quite a few months now and can confirm that it does indeed solve my problem. I am not a kernel developer, so I would appreciate if one of you could push this into the kernel tree. NOTE: I have attached Michel's patch with "(length > 1)" modified to "(length > 5)" and added a "Tested-by:". Thank you for testing this. I believe this code should go into the Linux kernel, since it closes up what could be a denial of service attack (albeit a local one) with the anonvma code. On Mon, Aug 20, 2012 at 02:39:26AM -0700, Michel Lespinasse wrote: Instead of adding an atomic count for page references, we could limit the anon_vma stacking depth. In fork, we would only clone anon_vmas that have a low enough generation count. I think that's not great (adds a special case for the deep-fork-without-exec behavior), but still better than the atomic page reference counter. Here is an attached patch to demonstrate the idea. anon_vma_clone() is modified to return the length of the existing same_vma anon vma chain, and we create a new anon_vma in the child only on the first fork (this could be tweaked to allow up to a set number of forks, but I think the first fork would cover all the common forking server cases). Signed-off-by: Michel Lespinasse Tested-by: Daniel Forrest Reviewed-by: Rik van Riel -- All rights reversed -- 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: [RFC PATCH] Re: Repeated fork() causes SLAB to grow without bound
On 06/03/2013 03:50 PM, Daniel Forrest wrote: On Tue, Aug 21, 2012 at 11:29:54PM -0400, Rik van Riel wrote: On 08/21/2012 11:20 PM, Michel Lespinasse wrote: On Mon, Aug 20, 2012 at 02:39:26AM -0700, Michel Lespinasse wrote: Instead of adding an atomic count for page references, we could limit the anon_vma stacking depth. In fork, we would only clone anon_vmas that have a low enough generation count. I think that's not great (adds a special case for the deep-fork-without-exec behavior), but still better than the atomic page reference counter. Here is an attached patch to demonstrate the idea. anon_vma_clone() is modified to return the length of the existing same_vma anon vma chain, and we create a new anon_vma in the child only on the first fork (this could be tweaked to allow up to a set number of forks, but I think the first fork would cover all the common forking server cases). I suspect we need 2 or 3. Some forking servers first fork off one child, and have the original parent exit, in order to background the server. That first child then becomes the parent to the real child processes that do the work. It is conceivable that we might need an extra level for processes that do something special with privilege dropping, namespace changing, etc... Even setting the threshold to 5 should be totally harmless, since the problem does not kick in until we have really long chains, like in Dan's bug report. I have been running with Michel's patch (with the threshold set to 5) for quite a few months now and can confirm that it does indeed solve my problem. I am not a kernel developer, so I would appreciate if one of you could push this into the kernel tree. NOTE: I have attached Michel's patch with (length 1) modified to (length 5) and added a Tested-by:. Thank you for testing this. I believe this code should go into the Linux kernel, since it closes up what could be a denial of service attack (albeit a local one) with the anonvma code. On Mon, Aug 20, 2012 at 02:39:26AM -0700, Michel Lespinasse wrote: Instead of adding an atomic count for page references, we could limit the anon_vma stacking depth. In fork, we would only clone anon_vmas that have a low enough generation count. I think that's not great (adds a special case for the deep-fork-without-exec behavior), but still better than the atomic page reference counter. Here is an attached patch to demonstrate the idea. anon_vma_clone() is modified to return the length of the existing same_vma anon vma chain, and we create a new anon_vma in the child only on the first fork (this could be tweaked to allow up to a set number of forks, but I think the first fork would cover all the common forking server cases). Signed-off-by: Michel Lespinasse wal...@google.com Tested-by: Daniel Forrest dan.forr...@ssec.wisc.edu Reviewed-by: Rik van Riel r...@redhat.com -- All rights reversed -- 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: [RFC PATCH] Re: Repeated fork() causes SLAB to grow without bound
On Tue, Aug 21, 2012 at 11:29:54PM -0400, Rik van Riel wrote:
> On 08/21/2012 11:20 PM, Michel Lespinasse wrote:
> >On Mon, Aug 20, 2012 at 02:39:26AM -0700, Michel Lespinasse wrote:
> >>Instead of adding an atomic count for page references, we could limit
> >>the anon_vma stacking depth. In fork, we would only clone anon_vmas
> >>that have a low enough generation count. I think that's not great
> >>(adds a special case for the deep-fork-without-exec behavior), but
> >>still better than the atomic page reference counter.
> >
> >Here is an attached patch to demonstrate the idea.
> >
> >anon_vma_clone() is modified to return the length of the existing same_vma
> >anon vma chain, and we create a new anon_vma in the child only on the first
> >fork (this could be tweaked to allow up to a set number of forks, but
> >I think the first fork would cover all the common forking server cases).
>
> I suspect we need 2 or 3.
>
> Some forking servers first fork off one child, and have
> the original parent exit, in order to "background the server".
> That first child then becomes the parent to the real child
> processes that do the work.
>
> It is conceivable that we might need an extra level for
> processes that do something special with privilege dropping,
> namespace changing, etc...
>
> Even setting the threshold to 5 should be totally harmless,
> since the problem does not kick in until we have really
> long chains, like in Dan's bug report.
I have been running with Michel's patch (with the threshold set to 5)
for quite a few months now and can confirm that it does indeed solve
my problem. I am not a kernel developer, so I would appreciate if one
of you could push this into the kernel tree.
NOTE: I have attached Michel's patch with "(length > 1)" modified to
"(length > 5)" and added a "Tested-by:".
---
On Mon, Aug 20, 2012 at 02:39:26AM -0700, Michel Lespinasse wrote:
> Instead of adding an atomic count for page references, we could limit
> the anon_vma stacking depth. In fork, we would only clone anon_vmas
> that have a low enough generation count. I think that's not great
> (adds a special case for the deep-fork-without-exec behavior), but
> still better than the atomic page reference counter.
Here is an attached patch to demonstrate the idea.
anon_vma_clone() is modified to return the length of the existing same_vma
anon vma chain, and we create a new anon_vma in the child only on the first
fork (this could be tweaked to allow up to a set number of forks, but
I think the first fork would cover all the common forking server cases).
Signed-off-by: Michel Lespinasse
Tested-by: Daniel Forrest
---
mm/mmap.c |6 +++---
mm/rmap.c | 18 ++
2 files changed, 17 insertions(+), 7 deletions(-)
diff --git a/mm/mmap.c b/mm/mmap.c
index 3edfcdfa42d9..e14b19a838cb 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -539,7 +539,7 @@ again: remove_next = 1 + (end >
next->vm_end);
* shrinking vma had, to cover any anon pages imported.
*/
if (exporter && exporter->anon_vma && !importer->anon_vma) {
- if (anon_vma_clone(importer, exporter))
+ if (anon_vma_clone(importer, exporter) < 0)
return -ENOMEM;
importer->anon_vma = exporter->anon_vma;
}
@@ -1988,7 +1988,7 @@ static int __split_vma(struct mm_struct * mm, struct
vm_area_struct * vma,
}
vma_set_policy(new, pol);
- if (anon_vma_clone(new, vma))
+ if (anon_vma_clone(new, vma) < 0)
goto out_free_mpol;
if (new->vm_file) {
@@ -2409,7 +2409,7 @@ struct vm_area_struct *copy_vma(struct vm_area_struct
**vmap,
if (IS_ERR(pol))
goto out_free_vma;
INIT_LIST_HEAD(_vma->anon_vma_chain);
- if (anon_vma_clone(new_vma, vma))
+ if (anon_vma_clone(new_vma, vma) < 0)
goto out_free_mempol;
vma_set_policy(new_vma, pol);
new_vma->vm_start = addr;
diff --git a/mm/rmap.c b/mm/rmap.c
index 0f3b7cda2a24..ba8a726aaee6 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -238,12 +238,13 @@ static inline void unlock_anon_vma_root(struct anon_vma
*root)
/*
* Attach the anon_vmas from src to dst.
- * Returns 0 on success, -ENOMEM on failure.
+ * Returns length of the anon_vma chain on success, -ENOMEM on failure.
*/
int anon_vma_clone(struct vm_area_struct *dst, struct vm_area_struct *src)
{
struct anon_vma_chain *avc, *pavc;
struct anon_vma *root = NULL;
+ int length = 0;
list_for_each_entry_reverse(pavc, >anon_vma_chain, same_vma) {
struct anon_vma *anon_vma;
@@ -259,9 +260,10 @@ int anon_vma_clone(struct vm_area_struct *dst, struct
vm_area_struct *src)
anon_vma =
Re: [RFC PATCH] Re: Repeated fork() causes SLAB to grow without bound
On Tue, Aug 21, 2012 at 11:29:54PM -0400, Rik van Riel wrote:
On 08/21/2012 11:20 PM, Michel Lespinasse wrote:
On Mon, Aug 20, 2012 at 02:39:26AM -0700, Michel Lespinasse wrote:
Instead of adding an atomic count for page references, we could limit
the anon_vma stacking depth. In fork, we would only clone anon_vmas
that have a low enough generation count. I think that's not great
(adds a special case for the deep-fork-without-exec behavior), but
still better than the atomic page reference counter.
Here is an attached patch to demonstrate the idea.
anon_vma_clone() is modified to return the length of the existing same_vma
anon vma chain, and we create a new anon_vma in the child only on the first
fork (this could be tweaked to allow up to a set number of forks, but
I think the first fork would cover all the common forking server cases).
I suspect we need 2 or 3.
Some forking servers first fork off one child, and have
the original parent exit, in order to background the server.
That first child then becomes the parent to the real child
processes that do the work.
It is conceivable that we might need an extra level for
processes that do something special with privilege dropping,
namespace changing, etc...
Even setting the threshold to 5 should be totally harmless,
since the problem does not kick in until we have really
long chains, like in Dan's bug report.
I have been running with Michel's patch (with the threshold set to 5)
for quite a few months now and can confirm that it does indeed solve
my problem. I am not a kernel developer, so I would appreciate if one
of you could push this into the kernel tree.
NOTE: I have attached Michel's patch with (length 1) modified to
(length 5) and added a Tested-by:.
---
On Mon, Aug 20, 2012 at 02:39:26AM -0700, Michel Lespinasse wrote:
Instead of adding an atomic count for page references, we could limit
the anon_vma stacking depth. In fork, we would only clone anon_vmas
that have a low enough generation count. I think that's not great
(adds a special case for the deep-fork-without-exec behavior), but
still better than the atomic page reference counter.
Here is an attached patch to demonstrate the idea.
anon_vma_clone() is modified to return the length of the existing same_vma
anon vma chain, and we create a new anon_vma in the child only on the first
fork (this could be tweaked to allow up to a set number of forks, but
I think the first fork would cover all the common forking server cases).
Signed-off-by: Michel Lespinasse wal...@google.com
Tested-by: Daniel Forrest dan.forr...@ssec.wisc.edu
---
mm/mmap.c |6 +++---
mm/rmap.c | 18 ++
2 files changed, 17 insertions(+), 7 deletions(-)
diff --git a/mm/mmap.c b/mm/mmap.c
index 3edfcdfa42d9..e14b19a838cb 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -539,7 +539,7 @@ again: remove_next = 1 + (end
next-vm_end);
* shrinking vma had, to cover any anon pages imported.
*/
if (exporter exporter-anon_vma !importer-anon_vma) {
- if (anon_vma_clone(importer, exporter))
+ if (anon_vma_clone(importer, exporter) 0)
return -ENOMEM;
importer-anon_vma = exporter-anon_vma;
}
@@ -1988,7 +1988,7 @@ static int __split_vma(struct mm_struct * mm, struct
vm_area_struct * vma,
}
vma_set_policy(new, pol);
- if (anon_vma_clone(new, vma))
+ if (anon_vma_clone(new, vma) 0)
goto out_free_mpol;
if (new-vm_file) {
@@ -2409,7 +2409,7 @@ struct vm_area_struct *copy_vma(struct vm_area_struct
**vmap,
if (IS_ERR(pol))
goto out_free_vma;
INIT_LIST_HEAD(new_vma-anon_vma_chain);
- if (anon_vma_clone(new_vma, vma))
+ if (anon_vma_clone(new_vma, vma) 0)
goto out_free_mempol;
vma_set_policy(new_vma, pol);
new_vma-vm_start = addr;
diff --git a/mm/rmap.c b/mm/rmap.c
index 0f3b7cda2a24..ba8a726aaee6 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -238,12 +238,13 @@ static inline void unlock_anon_vma_root(struct anon_vma
*root)
/*
* Attach the anon_vmas from src to dst.
- * Returns 0 on success, -ENOMEM on failure.
+ * Returns length of the anon_vma chain on success, -ENOMEM on failure.
*/
int anon_vma_clone(struct vm_area_struct *dst, struct vm_area_struct *src)
{
struct anon_vma_chain *avc, *pavc;
struct anon_vma *root = NULL;
+ int length = 0;
list_for_each_entry_reverse(pavc, src-anon_vma_chain, same_vma) {
struct anon_vma *anon_vma;
@@ -259,9 +260,10 @@ int anon_vma_clone(struct vm_area_struct *dst, struct
vm_area_struct *src)
anon_vma = pavc-anon_vma;
root =
Re: [RFC PATCH] Re: Repeated fork() causes SLAB to grow without bound
On 08/21/2012 11:20 PM, Michel Lespinasse wrote: On Mon, Aug 20, 2012 at 02:39:26AM -0700, Michel Lespinasse wrote: Instead of adding an atomic count for page references, we could limit the anon_vma stacking depth. In fork, we would only clone anon_vmas that have a low enough generation count. I think that's not great (adds a special case for the deep-fork-without-exec behavior), but still better than the atomic page reference counter. Here is an attached patch to demonstrate the idea. anon_vma_clone() is modified to return the length of the existing same_vma anon vma chain, and we create a new anon_vma in the child only on the first fork (this could be tweaked to allow up to a set number of forks, but I think the first fork would cover all the common forking server cases). I suspect we need 2 or 3. Some forking servers first fork off one child, and have the original parent exit, in order to "background the server". That first child then becomes the parent to the real child processes that do the work. It is conceivable that we might need an extra level for processes that do something special with privilege dropping, namespace changing, etc... Even setting the threshold to 5 should be totally harmless, since the problem does not kick in until we have really long chains, like in Dan's bug report. -- All rights reversed -- 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/
[RFC PATCH] Re: Repeated fork() causes SLAB to grow without bound
On Mon, Aug 20, 2012 at 02:39:26AM -0700, Michel Lespinasse wrote:
> Instead of adding an atomic count for page references, we could limit
> the anon_vma stacking depth. In fork, we would only clone anon_vmas
> that have a low enough generation count. I think that's not great
> (adds a special case for the deep-fork-without-exec behavior), but
> still better than the atomic page reference counter.
Here is an attached patch to demonstrate the idea.
anon_vma_clone() is modified to return the length of the existing same_vma
anon vma chain, and we create a new anon_vma in the child only on the first
fork (this could be tweaked to allow up to a set number of forks, but
I think the first fork would cover all the common forking server cases).
Signed-off-by: Michel Lespinasse
---
mm/mmap.c |6 +++---
mm/rmap.c | 18 ++
2 files changed, 17 insertions(+), 7 deletions(-)
diff --git a/mm/mmap.c b/mm/mmap.c
index 3edfcdfa42d9..e14b19a838cb 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -539,7 +539,7 @@ again: remove_next = 1 + (end >
next->vm_end);
* shrinking vma had, to cover any anon pages imported.
*/
if (exporter && exporter->anon_vma && !importer->anon_vma) {
- if (anon_vma_clone(importer, exporter))
+ if (anon_vma_clone(importer, exporter) < 0)
return -ENOMEM;
importer->anon_vma = exporter->anon_vma;
}
@@ -1988,7 +1988,7 @@ static int __split_vma(struct mm_struct * mm, struct
vm_area_struct * vma,
}
vma_set_policy(new, pol);
- if (anon_vma_clone(new, vma))
+ if (anon_vma_clone(new, vma) < 0)
goto out_free_mpol;
if (new->vm_file) {
@@ -2409,7 +2409,7 @@ struct vm_area_struct *copy_vma(struct vm_area_struct
**vmap,
if (IS_ERR(pol))
goto out_free_vma;
INIT_LIST_HEAD(_vma->anon_vma_chain);
- if (anon_vma_clone(new_vma, vma))
+ if (anon_vma_clone(new_vma, vma) < 0)
goto out_free_mempol;
vma_set_policy(new_vma, pol);
new_vma->vm_start = addr;
diff --git a/mm/rmap.c b/mm/rmap.c
index 0f3b7cda2a24..ba8a726aaee6 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -238,12 +238,13 @@ static inline void unlock_anon_vma_root(struct anon_vma
*root)
/*
* Attach the anon_vmas from src to dst.
- * Returns 0 on success, -ENOMEM on failure.
+ * Returns length of the anon_vma chain on success, -ENOMEM on failure.
*/
int anon_vma_clone(struct vm_area_struct *dst, struct vm_area_struct *src)
{
struct anon_vma_chain *avc, *pavc;
struct anon_vma *root = NULL;
+ int length = 0;
list_for_each_entry_reverse(pavc, >anon_vma_chain, same_vma) {
struct anon_vma *anon_vma;
@@ -259,9 +260,10 @@ int anon_vma_clone(struct vm_area_struct *dst, struct
vm_area_struct *src)
anon_vma = pavc->anon_vma;
root = lock_anon_vma_root(root, anon_vma);
anon_vma_chain_link(dst, avc, anon_vma);
+ length++;
}
unlock_anon_vma_root(root);
- return 0;
+ return length;
enomem_failure:
unlink_anon_vmas(dst);
@@ -322,6 +324,7 @@ int anon_vma_fork(struct vm_area_struct *vma, struct
vm_area_struct *pvma)
{
struct anon_vma_chain *avc;
struct anon_vma *anon_vma;
+ int length;
/* Don't bother if the parent process has no anon_vma here. */
if (!pvma->anon_vma)
@@ -331,10 +334,17 @@ int anon_vma_fork(struct vm_area_struct *vma, struct
vm_area_struct *pvma)
* First, attach the new VMA to the parent VMA's anon_vmas,
* so rmap can find non-COWed pages in child processes.
*/
- if (anon_vma_clone(vma, pvma))
+ length = anon_vma_clone(vma, pvma);
+ if (length < 0)
return -ENOMEM;
+ else if (length > 1)
+ return 0;
- /* Then add our own anon_vma. */
+ /*
+* Then add our own anon_vma. We do this only on the first fork after
+* the anon_vma is created, as we don't want the same_vma chain to
+* grow arbitrarily large.
+*/
anon_vma = anon_vma_alloc();
if (!anon_vma)
goto out_error;
--
Michel "Walken" Lespinasse
A program is never fully debugged until the last user dies.
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[RFC PATCH] Re: Repeated fork() causes SLAB to grow without bound
On Mon, Aug 20, 2012 at 02:39:26AM -0700, Michel Lespinasse wrote:
Instead of adding an atomic count for page references, we could limit
the anon_vma stacking depth. In fork, we would only clone anon_vmas
that have a low enough generation count. I think that's not great
(adds a special case for the deep-fork-without-exec behavior), but
still better than the atomic page reference counter.
Here is an attached patch to demonstrate the idea.
anon_vma_clone() is modified to return the length of the existing same_vma
anon vma chain, and we create a new anon_vma in the child only on the first
fork (this could be tweaked to allow up to a set number of forks, but
I think the first fork would cover all the common forking server cases).
Signed-off-by: Michel Lespinasse wal...@google.com
---
mm/mmap.c |6 +++---
mm/rmap.c | 18 ++
2 files changed, 17 insertions(+), 7 deletions(-)
diff --git a/mm/mmap.c b/mm/mmap.c
index 3edfcdfa42d9..e14b19a838cb 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -539,7 +539,7 @@ again: remove_next = 1 + (end
next-vm_end);
* shrinking vma had, to cover any anon pages imported.
*/
if (exporter exporter-anon_vma !importer-anon_vma) {
- if (anon_vma_clone(importer, exporter))
+ if (anon_vma_clone(importer, exporter) 0)
return -ENOMEM;
importer-anon_vma = exporter-anon_vma;
}
@@ -1988,7 +1988,7 @@ static int __split_vma(struct mm_struct * mm, struct
vm_area_struct * vma,
}
vma_set_policy(new, pol);
- if (anon_vma_clone(new, vma))
+ if (anon_vma_clone(new, vma) 0)
goto out_free_mpol;
if (new-vm_file) {
@@ -2409,7 +2409,7 @@ struct vm_area_struct *copy_vma(struct vm_area_struct
**vmap,
if (IS_ERR(pol))
goto out_free_vma;
INIT_LIST_HEAD(new_vma-anon_vma_chain);
- if (anon_vma_clone(new_vma, vma))
+ if (anon_vma_clone(new_vma, vma) 0)
goto out_free_mempol;
vma_set_policy(new_vma, pol);
new_vma-vm_start = addr;
diff --git a/mm/rmap.c b/mm/rmap.c
index 0f3b7cda2a24..ba8a726aaee6 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -238,12 +238,13 @@ static inline void unlock_anon_vma_root(struct anon_vma
*root)
/*
* Attach the anon_vmas from src to dst.
- * Returns 0 on success, -ENOMEM on failure.
+ * Returns length of the anon_vma chain on success, -ENOMEM on failure.
*/
int anon_vma_clone(struct vm_area_struct *dst, struct vm_area_struct *src)
{
struct anon_vma_chain *avc, *pavc;
struct anon_vma *root = NULL;
+ int length = 0;
list_for_each_entry_reverse(pavc, src-anon_vma_chain, same_vma) {
struct anon_vma *anon_vma;
@@ -259,9 +260,10 @@ int anon_vma_clone(struct vm_area_struct *dst, struct
vm_area_struct *src)
anon_vma = pavc-anon_vma;
root = lock_anon_vma_root(root, anon_vma);
anon_vma_chain_link(dst, avc, anon_vma);
+ length++;
}
unlock_anon_vma_root(root);
- return 0;
+ return length;
enomem_failure:
unlink_anon_vmas(dst);
@@ -322,6 +324,7 @@ int anon_vma_fork(struct vm_area_struct *vma, struct
vm_area_struct *pvma)
{
struct anon_vma_chain *avc;
struct anon_vma *anon_vma;
+ int length;
/* Don't bother if the parent process has no anon_vma here. */
if (!pvma-anon_vma)
@@ -331,10 +334,17 @@ int anon_vma_fork(struct vm_area_struct *vma, struct
vm_area_struct *pvma)
* First, attach the new VMA to the parent VMA's anon_vmas,
* so rmap can find non-COWed pages in child processes.
*/
- if (anon_vma_clone(vma, pvma))
+ length = anon_vma_clone(vma, pvma);
+ if (length 0)
return -ENOMEM;
+ else if (length 1)
+ return 0;
- /* Then add our own anon_vma. */
+ /*
+* Then add our own anon_vma. We do this only on the first fork after
+* the anon_vma is created, as we don't want the same_vma chain to
+* grow arbitrarily large.
+*/
anon_vma = anon_vma_alloc();
if (!anon_vma)
goto out_error;
--
Michel Walken Lespinasse
A program is never fully debugged until the last user dies.
--
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: [RFC PATCH] Re: Repeated fork() causes SLAB to grow without bound
On 08/21/2012 11:20 PM, Michel Lespinasse wrote: On Mon, Aug 20, 2012 at 02:39:26AM -0700, Michel Lespinasse wrote: Instead of adding an atomic count for page references, we could limit the anon_vma stacking depth. In fork, we would only clone anon_vmas that have a low enough generation count. I think that's not great (adds a special case for the deep-fork-without-exec behavior), but still better than the atomic page reference counter. Here is an attached patch to demonstrate the idea. anon_vma_clone() is modified to return the length of the existing same_vma anon vma chain, and we create a new anon_vma in the child only on the first fork (this could be tweaked to allow up to a set number of forks, but I think the first fork would cover all the common forking server cases). I suspect we need 2 or 3. Some forking servers first fork off one child, and have the original parent exit, in order to background the server. That first child then becomes the parent to the real child processes that do the work. It is conceivable that we might need an extra level for processes that do something special with privilege dropping, namespace changing, etc... Even setting the threshold to 5 should be totally harmless, since the problem does not kick in until we have really long chains, like in Dan's bug report. -- All rights reversed -- 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/
