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    SubjectRe: suppress page allocation failure warnings from sys_listxattr
    On Tue, Mar 27, 2012 at 03:51:49PM -0700, Andrew Morton wrote:
    > On Tue, 13 Mar 2012 14:22:20 -0400
    > Dave Jones <davej@redhat.com> wrote:
    >
    > > This size is user controllable, and so it's trivial for someone to trigger a
    > > stream of order:4 page allocation errors.
    > >
    > > Signed-off-by: Dave Jones <davej@redhat.com>
    > >
    > > ---
    > > There's also a similar problem in setxattr, but I'm not sure how we want
    > > to pass NOWARN down to memdup_user. Thoughts ?
    > >
    > > diff --git a/fs/xattr.c b/fs/xattr.c
    > > index 82f4337..544df90 100644
    > > --- a/fs/xattr.c
    > > +++ b/fs/xattr.c
    > > @@ -496,7 +496,7 @@ listxattr(struct dentry *d, char __user *list, size_t size)
    > > if (size) {
    > > if (size > XATTR_LIST_MAX)
    > > size = XATTR_LIST_MAX;
    > > - klist = kmalloc(size, GFP_KERNEL);
    > > + klist = kmalloc(size, __GFP_NOWARN | GFP_KERNEL);
    > > if (!klist)
    > > return -ENOMEM;
    > > }
    >
    > hm. The patch is good, but one would hope that it isn't "trivial" to
    > trigger a page allocation failure for a kmalloc(65536, GFP_KERNEL) -
    > the VM is supposed to be able to handle that.
    >
    > Is it really *that* easy, or is Something Unusual happening with that
    > machine?

    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.

    Dave


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