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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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