slab: prevent warnings when allocating with __GFP_NOWARN

Sasha Levin noticed that the warning introduced by commit 6286ae9
("slab: Return NULL for oversized allocations) is being triggered:

  WARNING: CPU: 15 PID: 21519 at mm/slab_common.c:376 kmalloc_slab+0x2f/0xb0()
  can: request_module (can-proto-4) failed.
  mpoa: proc_mpc_write: could not parse ''
  Modules linked in:
  CPU: 15 PID: 21519 Comm: trinity-child15 Tainted: G W    3.10.0-rc4-next-20130607-sasha-00011-gcd78395-dirty #2
   0000000000000009 ffff880020a95e30 ffffffff83ff4041 0000000000000000
   ffff880020a95e68 ffffffff8111fe12 fffffffffffffff0 00000000000082d0
   0000000000080000 0000000000080000 0000000001400000 ffff880020a95e78
  Call Trace:
   [<ffffffff83ff4041>] dump_stack+0x4e/0x82
   [<ffffffff8111fe12>] warn_slowpath_common+0x82/0xb0
   [<ffffffff8111fe55>] warn_slowpath_null+0x15/0x20
   [<ffffffff81243dcf>] kmalloc_slab+0x2f/0xb0
   [<ffffffff81278d54>] __kmalloc+0x24/0x4b0
   [<ffffffff8196ffe3>] ? security_capable+0x13/0x20
   [<ffffffff812a26b7>] ? pipe_fcntl+0x107/0x210
   [<ffffffff812a26b7>] pipe_fcntl+0x107/0x210
   [<ffffffff812b7ea0>] ? fget_raw_light+0x130/0x3f0
   [<ffffffff812aa5fb>] SyS_fcntl+0x60b/0x6a0
   [<ffffffff8403ca98>] tracesys+0xe1/0xe6

Andrew Morton writes:

  __GFP_NOWARN is frequently used by kernel code to probe for "how big
  an allocation can I get".  That's a bit lame, but it's used on slow
  paths and is pretty simple.

However, SLAB would still spew a warning when a big allocation happens
if the __GFP_NOWARN flag is _not_ set to expose kernel bugs.

Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
[ penberg@kernel.org: improve changelog ]
Signed-off-by: Pekka Enberg <penberg@kernel.org>

diff --git a/mm/slab_common.c b/mm/slab_common.c
index ff3218a0f5e14029aab5c23dd323f447d2a86173..2d414508e9ecb32e64df911c72bf0dd2682b87b8 100644 (file)
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -373,8 +373,10 @@ struct kmem_cache *kmalloc_slab(size_t size, gfp_t flags)
 {
        int index;
 
-       if (WARN_ON_ONCE(size > KMALLOC_MAX_SIZE))
+       if (size > KMALLOC_MAX_SIZE) {
+               WARN_ON_ONCE(!(flags & __GFP_NOWARN));
                return NULL;
+       }
 
        if (size <= 192) {
                if (!size)