linux-kernel - Re: [PATCH] slob/lockdep: Fix gfp flags passed to lockdep

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Message-ID: <BANLkTinUcZFW6-GKQgWn-KhzEA0Qbaz8PA@mail.gmail.com>
Date:	Tue, 7 Jun 2011 14:54:14 +0300
From:	Pekka Enberg <penberg@...nel.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Matt Mackall <mpm@...enic.com>,
	Paul Mundt <lethal@...ux-sh.org>,
	Nick Piggin <npiggin@...nel.dk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Lameter <cl@...ux.com>,
	David Rientjes <rientjes@...gle.com>
Subject: Re: [PATCH] slob/lockdep: Fix gfp flags passed to lockdep

On Tue, Jun 7, 2011 at 2:18 PM, Steven Rostedt <rostedt@...dmis.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@...enic.com>
> Cc: Paul Mundt <lethal@...ux-sh.org>
> Cc: Nick Piggin <npiggin@...nel.dk>
> Signed-off-by: Steven Rostedt <rostedt@...dmis.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?
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