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SubjectRe: suppress page allocation failure warnings from sys_listxattr
On Wed, 28 Mar 2012 20:54:42 -0400 Dave Jones <davej@redhat.com> wrote:

> On Wed, Mar 28, 2012 at 04:47:20PM -0700, Andrew Morton wrote:
> > On Wed, 28 Mar 2012 15:39:51 +1100
> > Dave Chinner <david@fromorbit.com> wrote:
> >
> > > > Well, the unusual thing was that I was fuzzing system calls for a few hours.
> > > >
> > > > My fuzzing tool was able to trigger these very easily after an hour or two
> > > > of uptime and memory had fragmented a little, so yeah, quite trivial.
> > >
> > > We've recently been seeing reports of xfsdump trigging a similar
> > > allocation failures in the XFS attr code when we are doing hundreds
> > > of thousands of attribute lookups to back them up.
> > >
> > > ad650f5 xfs: fallback to vmalloc for large buffers in xfs_attrmulti_attr_get
> > >
> > > I think that falling back to vmalloc here is much better solution
> > > than failing to retreive the attribute - it will work no matter how
> > > fragmented memory gets. That means we don't get incomplete
> > > backups occurring after days or months of uptime and successful
> > > backups...
> >
> > Yup. How does the below look?
>
> Don't see anything immediately wrong with it.
> Any thoughts on what to do about the similar problem in setxattr ? (memdup_user)
>

I can't think of anything clever.

The dumb approach:

From: Andrew Morton <akpm@linux-foundation.org>
Subject: fs/xattr.c:setxattr(): improve handling of allocation failures

This allocation can be as large as 64k.

- Add __GFP_NOWARN so that a falied kmalloc() is silent

- Fall back to vmalloc() if the kmalloc() failed

Cc: Dave Chinner <david@fromorbit.com>
Cc: Dave Jones <davej@codemonkey.org.uk>
Cc: David Rientjes <rientjes@google.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
fs/xattr.c | 21 +++++++++++++++++----
1 file changed, 17 insertions(+), 4 deletions(-)
diff -puN fs/xattr.c~fs-xattrc-setxattr-improve-handling-of-allocation-failures fs/xattr.c
--- a/fs/xattr.c~fs-xattrc-setxattr-improve-handling-of-allocation-failures
+++ a/fs/xattr.c
@@ -320,6 +320,7 @@ setxattr(struct dentry *d, const char __
{
int error;
void *kvalue = NULL;
+ void *vvalue = NULL; /* If non-NULL, we used vmalloc() */
char kname[XATTR_NAME_MAX + 1];

if (flags & ~(XATTR_CREATE|XATTR_REPLACE))
@@ -334,13 +335,25 @@ setxattr(struct dentry *d, const char __
if (size) {
if (size > XATTR_SIZE_MAX)
return -E2BIG;
- kvalue = memdup_user(value, size);
- if (IS_ERR(kvalue))
- return PTR_ERR(kvalue);
+ kvalue = kmalloc(size, GFP_KERNEL | __GFP_NOWARN);
+ if (!kvalue) {
+ vvalue = vmalloc(size);
+ if (!vvalue)
+ return -ENOMEM;
+ kvalue = vvalue;
+ }
+ if (copy_from_user(kvalue, value, size)) {
+ error = -EFAULT;
+ goto out;
+ }
}

error = vfs_setxattr(d, kname, kvalue, size, flags);
- kfree(kvalue);
+out:
+ if (vvalue)
+ vfree(vvalue);
+ else
+ kfree(kvalue);
return error;
}

_


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