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

[Sasha Levin]

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@xxxxxxxxxx> 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@xxxxxxxxxx>
> > ---
> >   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
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/