linux-kernel - Re: suppress page allocation failure warnings from sys

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Message-ID: <20120329211315.GB18684@redhat.com>
Date:	Thu, 29 Mar 2012 17:13:15 -0400
From:	Dave Jones <davej@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Joe Perches <joe@...ches.com>, Dave Chinner <david@...morbit.com>,
	viro@...iv.linux.org.uk,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	David Rientjes <rientjes@...gle.com>
Subject: Re: suppress page allocation failure warnings from sys_listxattr

On Thu, Mar 29, 2012 at 02:09:34PM -0700, Andrew Morton wrote:
 > On Wed, 28 Mar 2012 23:00:00 -0400
 > Dave Jones <davej@...hat.com> wrote:
 > 
 > > On Wed, Mar 28, 2012 at 07:28:04PM -0700, Andrew Morton wrote:
 > >  > > But it looks like
 > >  > > key_add (see other thread from this evening) and probably others can be
 > >  > > called as a user and gobble up vmalloc space. omnomnom.
 > >  > 
 > >  > hm, the keys code appears to prevent the user from reserving more than
 > >  > 20000 bytes of memory total (key_payload_reserve()), so it doesn't look
 > >  > very useful for screwing up vmalloc().
 > > 
 > > Then how did I trick it into trying an order 8 allocation ?
 > > 
 > > trinity: page allocation failure: order:8, mode:0x40d0
 > > Pid: 27119, comm: trinity Not tainted 3.3.0+ #31
 > > Call Trace:
 > >  [<ffffffff8115dd66>] warn_alloc_failed+0xf6/0x160
 > >  [<ffffffff816ad436>] ? __alloc_pages_direct_compact+0x1d0/0x1e2
 > >  [<ffffffff81162492>] __alloc_pages_nodemask+0x8b2/0xb10
 > >  [<ffffffff8119dae6>] alloc_pages_current+0xb6/0x120
 > >  [<ffffffff8115d3b4>] __get_free_pages+0x14/0x50
 > >  [<ffffffff811ac64f>] kmalloc_order_trace+0x3f/0x1a0
 > >  [<ffffffff811aca0a>] __kmalloc+0x25a/0x280
 > >  [<ffffffff812c034a>] sys_add_key+0x9a/0x210
 > >  [<ffffffff813386be>] ? trace_hardirqs_on_thunk+0x3a/0x3f
 > >  [<ffffffff816c04e9>] system_call_fastpath+0x16/0x1b
 > 
 > Ah, that's different.  The memory at *payload doesn't live beyond the
 > syscall so it can't be used to cause vmalloc fragmentation.
 > 
 > We should squish the warning:

That's the same patch I sent in the other thread, so ack ;-)

	Dave
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