linux-kernel - Re: [PATCH 1/3] tracing/mm: Don't trace kmem_cache

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Message-ID: <CAM4v1pMepumQWdEp3F5MFTGdJk2g=9ELQWbci_jyg5Fce55e8A@mail.gmail.com>
Date:	Wed, 29 Apr 2015 14:34:06 +0530
From:	Preeti Murthy <preeti.lkml@...il.com>
To:	"Shreyas B. Prabhu" <shreyas@...ux.vnet.ibm.com>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>
Cc:	LKML <linux-kernel@...r.kernel.org>, rostedt@...dmis.org,
	Ingo Molnar <mingo@...hat.com>,
	aneesh.kumar@...ux.vnet.ibm.com,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>
Subject: Re: [PATCH 1/3] tracing/mm: Don't trace kmem_cache_free on offline cpus

Ccing Paul,

On Tue, Apr 28, 2015 at 9:21 PM, Shreyas B. Prabhu
<shreyas@...ux.vnet.ibm.com> wrote:
> Since tracepoints use RCU for protection, they must not be called on
> offline cpus. trace_kmem_cache_free can be called on an offline cpu in
> this scenario caught by LOCKDEP:
>
> ===============================
> [ INFO: suspicious RCU usage. ]
> 4.1.0-rc1+ #9 Not tainted
> -------------------------------
> include/trace/events/kmem.h:148 suspicious rcu_dereference_check() usage!
>
> other info that might help us debug this:
>
> RCU used illegally from offline CPU!
> rcu_scheduler_active = 1, debug_locks = 1
> no locks held by swapper/1/0.
>
> stack backtrace:
> CPU: 1 PID: 0 Comm: swapper/1 Not tainted 4.1.0-rc1+ #9
> Call Trace:
> [c000001fed2f78f0] [c0000000009dee8c] .dump_stack+0x98/0xd4 (unreliable)
> [c000001fed2f7970] [c000000000128d88] .lockdep_rcu_suspicious+0x108/0x170
> [c000001fed2f7a00] [c00000000026f924] .kmem_cache_free+0x344/0x4b0
> [c000001fed2f7ab0] [c0000000000bd1cc] .__mmdrop+0x4c/0x160
> [c000001fed2f7b40] [c0000000001068e0] .idle_task_exit+0xf0/0x100
> [c000001fed2f7bc0] [c000000000066948] .pnv_smp_cpu_kill_self+0x58/0x2c0
> [c000001fed2f7ca0] [c00000000003ce34] .cpu_die+0x34/0x50
> [c000001fed2f7d10] [c0000000000176d0] .arch_cpu_idle_dead+0x20/0x40
> [c000001fed2f7d80] [c00000000011f9a8] .cpu_startup_entry+0x708/0x7a0
> [c000001fed2f7ec0] [c00000000003cb6c] .start_secondary+0x36c/0x3a0
> [c000001fed2f7f90] [c000000000008b6c] start_secondary_prolog+0x10/0x14
>
> Fix this by converting kmem_cache_free trace point into TRACE_EVENT_CONDITION
> where condition is cpu_online(smp_processor_id())
>
> Signed-off-by: Shreyas B. Prabhu <shreyas@...ux.vnet.ibm.com>
> Reported-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>
> ---
>  include/trace/events/kmem.h | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/include/trace/events/kmem.h b/include/trace/events/kmem.h
> index 81ea598..dd9e612 100644
> --- a/include/trace/events/kmem.h
> +++ b/include/trace/events/kmem.h
> @@ -140,11 +140,13 @@ DEFINE_EVENT(kmem_free, kfree,
>         TP_ARGS(call_site, ptr)
>  );
>
> -DEFINE_EVENT(kmem_free, kmem_cache_free,
> +DEFINE_EVENT_CONDITION(kmem_free, kmem_cache_free,
>
>         TP_PROTO(unsigned long call_site, const void *ptr),
>
> -       TP_ARGS(call_site, ptr)
> +       TP_ARGS(call_site, ptr),
> +
> +       TP_CONDITION(cpu_online(smp_processor_id()))
>  );
>
>  TRACE_EVENT(mm_page_free,

Reviewed-by: Preeti U Murthy <preeti@...ux.vnet.ibm.com>

Regards
Preeti U Murthy
> --
> 1.9.3
>
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