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Subject: Re: [PATCH] slob/lockdep: Fix gfp flags passed to lockdep
From: Matt Mackall <mpm@selenic.com>
To: Pekka Enberg <penberg@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>, LKML <linux-kernel@vger.kernel.org>,
        Ingo Molnar <mingo@elte.hu>, Paul Mundt <lethal@linux-sh.org>,
        Nick Piggin <npiggin@kernel.dk>,
        Andrew Morton <akpm@linux-foundation.org>,
        Christoph Lameter <cl@linux.com>, David Rientjes <rientjes@google.com>
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Date: Tue, 07 Jun 2011 07:49:06 -0500
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On Tue, 2011-06-07 at 14:54 +0300, Pekka Enberg wrote:
> On Tue, Jun 7, 2011 at 2:18 PM, Steven Rostedt <rostedt@goodmis.org> wrote:
> >
> > Doing a ktest.pl randconfig, I stumbled across the following bug
> > on boot up:
> >
> > ------------[ cut here ]------------
> > WARNING: at /home/rostedt/work/autotest/nobackup/linux-test.git/kernel/lockdep.c:2649 lockdep_trace_alloc+0xed/0x100()
> > Hardware name:
> > Modules linked in:
> > Pid: 0, comm: swapper Not tainted 3.0.0-rc1-test-00054-g1d68b67 #1
> > Call Trace:
> >  [<ffffffff810626ad>] warn_slowpath_common+0xad/0xf0
> >  [<ffffffff8106270a>] warn_slowpath_null+0x1a/0x20
> >  [<ffffffff810b537d>] lockdep_trace_alloc+0xed/0x100
> >  [<ffffffff81182fb0>] __kmalloc_node+0x30/0x2f0
> >  [<ffffffff81153eda>] pcpu_mem_alloc+0x13a/0x180
> >  [<ffffffff82be022c>] percpu_init_late+0x48/0xc2
> >  [<ffffffff82bd630c>] ? mem_init+0xd8/0xe3
> >  [<ffffffff82bbcc73>] start_kernel+0x1c2/0x449
> >  [<ffffffff82bbc35c>] x86_64_start_reservations+0x163/0x167
> >  [<ffffffff82bbc493>] x86_64_start_kernel+0x133/0x142^M
> > ---[ end trace a7919e7f17c0a725 ]---
> >
> > Then I ran a ktest.pl config_bisect and it came up with this config
> > as the problem:
> >
> >  CONFIG_SLOB
> >
> > Looking at what is different between SLOB and SLAB and SLUB, I found
> > that the gfp flags are masked against gfp_allowed_mask in
> > SLAB and SLUB, but not SLOB.
> >
> > On boot up, interrupts are disabled and lockdep will warn if some flags
> > are set in gfp and interrupts are disabled. But these flags are masked
> > off with the gfp_allowed_mask during boot. Because SLOB does not
> > mask the flags against gfp_allowed_mask it triggers the warn on.
> >
> > Adding this mask fixes the bug. I also found that kmem_cache_alloc_node()
> > was missing both the mask and the lockdep check, and that was added too.
> >
> > Cc: Matt Mackall <mpm@selenic.com>
> > Cc: Paul Mundt <lethal@linux-sh.org>
> > Cc: Nick Piggin <npiggin@kernel.dk>
> > Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
> >
> > diff --git a/mm/slob.c b/mm/slob.c
> > index 46e0aee..0ae8818 100644
> > --- a/mm/slob.c
> > +++ b/mm/slob.c
> > @@ -482,6 +482,8 @@ void *__kmalloc_node(size_t size, gfp_t gfp, int node)
> >        int align = max(ARCH_KMALLOC_MINALIGN, ARCH_SLAB_MINALIGN);
> >        void *ret;
> >
> > +       gfp &= gfp_allowed_mask;
> > +
> >        lockdep_trace_alloc(gfp);
> >
> >        if (size < PAGE_SIZE - align) {
> > @@ -608,6 +610,10 @@ void *kmem_cache_alloc_node(struct kmem_cache *c, gfp_t flags, int node)
> >  {
> >        void *b;
> >
> > +       flags &= gfp_allowed_mask;
> > +
> > +       lockdep_trace_alloc(flags);
> > +
> >        if (c->size < PAGE_SIZE) {
> >                b = slob_alloc(c->size, flags, c->align, node);
> >                trace_kmem_cache_alloc_node(_RET_IP_, b, c->size,
> 
> Matt, any objections to merging this?

Looks good.

Acked-by: Matt Mackall <mpm@selenic.com>


-- 
Mathematics is the supreme nostalgia of our time.


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