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Message-ID: <470F40C4.1050901@freedesktop.org>
Date: Fri, 12 Oct 2007 02:39:16 -0700
From: Josh Triplett <josh@freedesktop.org>
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To: ego@in.ibm.com
CC: Paul E McKenney <paulmck@us.ibm.com>, linux-kernel@vger.kernel.org,
       Andrew Morton <akpm@linux-foundation.org>,
       Oleg Nesterov <oleg@tv-sign.ru>, Dipankar Sarma <dipankar@in.ibm.com>,
       rostedt@goodmis.org
Subject: Re: [PATCH] Use raw_smp_processor_id() in rcu_random()
References: <20071012092044.GA1138@in.ibm.com>
In-Reply-To: <20071012092044.GA1138@in.ibm.com>
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Gautham R Shenoy wrote:
> With CONFIG_PREEMPT=y on 2.6.23-rc8-mm2, rcu_random() calls 
> smp_processor_id() from a preemptible context, triggering the
> following kernel error.
> 
> BUG: using smp_processor_id() in preemptible [00000001] code: rcu_torture_fak/5155
> caller is rcu_random+0x16/0x39 [rcutorture]
>  [<c010612f>] dump_trace+0x68/0x1d2
>  [<c01062b1>] show_trace_log_lvl+0x18/0x2c
>  [<c0106c23>] show_trace+0xf/0x11
>  [<c0106d33>] dump_stack+0x12/0x14
>  [<c02a0a25>] debug_smp_processor_id+0xa1/0xb4
>  [<f887064c>] rcu_random+0x16/0x39 [rcutorture]
>  [<f8870cdf>] <3>BUG: using smp_processor_id() in preemptible [00000001] code: rcu_torture_fak/5156
> rcu_torture_fakewriter+0x4d/0xc5 [rcutorture]
>  [<c0139b32>] caller is rcu_random+0x16/0x39 [rcutorture]
> kthread+0x38/0x5e
>  [<c0105ca7>] kernel_thread_helper+0x7/0x10
>  =======================
>  [<c010612f>] dump_trace+0x68/0x1d2
>  [<c01062b1>] show_trace_log_lvl+0x18/0x2c
>  [<c0106c23>] show_trace+0xf/0x11
>  [<c0106d33>] dump_stack+0x12/0x14
>  [<c02a0a25>] debug_smp_processor_id+0xa1/0xb4
>  [<f887064c>] rcu_random+0x16/0x39 [rcutorture]
>  [<f8870cdf>] rcu_torture_fakewriter+0x4d/0xc5 [rcutorture]
> 
> rcu_random() can do with raw_smp_processor_id() as a parameter to cpu_clock()
> in this particular context.
> 
> Signed-off-by: Gautham R Shenoy <ego@in.ibm.com>

Looks reasonable to me.

Acked-by: Josh Triplett <josh@kernel.org> 

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