Re: [PATCH] slab: prevent warnings when allocating with __GFP_NOWARN

Sasha Levin
2013-06-10T19:56:35Z

On 06/10/2013 03:31 PM, Pekka Enberg wrote:
> Hello Sasha,
>
> On Mon, Jun 10, 2013 at 10:18 PM, Sasha Levin <sasha.levin@oracle.com> wrote:
>> slab would still spew a warning when a big allocation happens with the
>> __GFP_NOWARN fleg is set. Prevent that to conform to __GFP_NOWARN.
>>
>> Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
>> ---
>> mm/slab_common.c | 4 +++-
>> 1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/mm/slab_common.c b/mm/slab_common.c
>> index ff3218a..2d41450 100644
>> --- 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;
>> + }
>
> Does this fix a real problem you're seeing? __GFP_NOWARN is about not
> warning if a memory allocation fails but this particular WARN_ON
> suggests a kernel bug.

It fixes this warning:

[ 1691.703002] WARNING: CPU: 15 PID: 21519 at mm/slab_common.c:376
kmalloc_slab+0x2f/0xb0()
[ 1691.706906] can: request_module (can-proto-4) failed.
[ 1691.707827] mpoa: proc_mpc_write: could not parse ''
[ 1691.713952] Modules linked in:
[ 1691.715199] CPU: 15 PID: 21519 Comm: trinity-child15 Tainted: G
W 3.10.0-rc4-next-20130607-sasha-00011-gcd78395-dirty #2
[ 1691.719669] 0000000000000009 ffff880020a95e30 ffffffff83ff4041
0000000000000000
[ 1691.797744] ffff880020a95e68 ffffffff8111fe12 fffffffffffffff0
00000000000082d0
[ 1691.802822] 0000000000080000 0000000000080000 0000000001400000
ffff880020a95e78
[ 1691.807621] Call Trace:
[ 1691.809473] [<ffffffff83ff4041>] dump_stack+0x4e/0x82
[ 1691.812783] [<ffffffff8111fe12>] warn_slowpath_common+0x82/0xb0
[ 1691.817011] [<ffffffff8111fe55>] warn_slowpath_null+0x15/0x20
[ 1691.819936] [<ffffffff81243dcf>] kmalloc_slab+0x2f/0xb0
[ 1691.824942] [<ffffffff81278d54>] __kmalloc+0x24/0x4b0
[ 1691.827285] [<ffffffff8196ffe3>] ? security_capable+0x13/0x20
[ 1691.829405] [<ffffffff812a26b7>] ? pipe_fcntl+0x107/0x210
[ 1691.831827] [<ffffffff812a26b7>] pipe_fcntl+0x107/0x210
[ 1691.833651] [<ffffffff812b7ea0>] ? fget_raw_light+0x130/0x3f0
[ 1691.835343] [<ffffffff812aa5fb>] SyS_fcntl+0x60b/0x6a0
[ 1691.837008] [<ffffffff8403ca98>] tracesys+0xe1/0xe6

The caller specifically sets __GFP_NOWARN presumably to avoid this
warning on slub but I'm not sure if there's any other reason.

Thanks,
Sasha