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    SubjectRe: suppress page allocation failure warnings from sys_listxattr
    On Wed, Mar 28, 2012 at 06:46:02PM -0700, Andrew Morton wrote:
    > On Wed, 28 Mar 2012 18:28:43 -0700 Joe Perches <joe@perches.com> wrote:
    >
    > > On Wed, 2012-03-28 at 18:10 -0700, Andrew Morton wrote:
    > > > On Wed, 28 Mar 2012 20:54:42 -0400 Dave Jones <davej@redhat.com> wrote:
    > > > > > 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)
    > > []
    > > > diff -puN fs/xattr.c~fs-xattrc-setxattr-improve-handling-of-allocation-failures fs/xattr.c
    > > []
    > > > @@ -334,13 +335,25 @@ setxattr(struct dentry *d, const char __
    > > []
    > > > + kvalue = kmalloc(size, GFP_KERNEL | __GFP_NOWARN);
    > > > + if (!kvalue) {
    > > > + vvalue = vmalloc(size);
    > > []
    > > > + if (vvalue)
    > > > + vfree(vvalue);
    > > > + else
    > > > + kfree(kvalue);
    > > > return error;
    > >
    > > These patterns are pretty common, maybe create a standard helper?
    >
    > Could. There was some discussion last year and implementations were
    > tossed around.
    >
    > I'm a bit apprehensive - kernel code is supposed to be robust, and
    > large allocations are not robust and vmalloc() is crappy. Formalising
    > these things in an API probably won't make anything worse, but will
    > deprive us of opportunities for ritualistic humiliation and
    > knuckle-rapping.

    I did a sweep of this recently, considering helpers for exactly such
    an allocation and replacing the existing per-filesystem wrappers for
    it. IIRC, there are wrappper functions in ext4, gfs2, and ntfs, XFS
    now open codes it in a couple of places, there's alloc_fdmem(), cgroup
    pidlists and the network code does it in several places, etc.
    Even some drivers are doing this. It's a widespread pattern.

    The easiest way to find the trivial wrappers is to grep for
    is_vmalloc_addr, because all the wrapper functions use this code to
    determine what to do:

    if (is_vmalloc_addr(p))
    vfree(p)
    else
    kfree(p)

    Cheers,

    Dave.
    --
    Dave Chinner
    david@fromorbit.com


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