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Date: Tue, 27 Mar 2012 17:26:22 -0700 From: Andrew Morton <akpm@...ux-foundation.org> To: Dave Jones <davej@...hat.com> Cc: viro@...iv.linux.org.uk, Linux Kernel <linux-kernel@...r.kernel.org> Subject: Re: suppress page allocation failure warnings from sys_listxattr On Tue, 27 Mar 2012 20:15:50 -0400 Dave Jones <davej@...hat.com> wrote: > 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@...hat.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@...hat.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. > /* * PAGE_ALLOC_COSTLY_ORDER is the order at which allocations are deemed * costly to service. That is between allocation orders which should * coelesce naturally under reasonable reclaim pressure and those which * will not. */ #define PAGE_ALLOC_COSTLY_ORDER 3 Death to magic numbers :( -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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