linux-kernel - Re: [PATCH] trace: disable preemption before taking raw spinlocks

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Date:	Tue, 26 May 2009 23:51:40 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Heiko Carstens <heiko.carstens@...ibm.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>, Ingo Molnar <mingo@...e.hu>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] trace: disable preemption before taking raw spinlocks

On Tue, 2009-05-26 at 17:28 +0200, Heiko Carstens wrote:
> From: Heiko Carstens <heiko.carstens@...ibm.com>
> 
> s390 code uses smp_processor_id() in __raw_spin_lock() code which
> reveals that a (raw) spinlock is taken without preemption disabled.
> This can potentially deadlock.
> 
> To fix this explicitly disable and enable preemption.
> 
> BUG: using smp_processor_id() in preemptible [00000000] code: cat/2278
> caller is trace_find_cmdline+0x40/0xfc
> CPU: 0 Not tainted 2.6.30-rc7-dirty #39
> Process cat (pid: 2278, task: 000000003faedb68, ksp: 000000003b33b988)
> 000000003b33b988 000000003b33bae0 0000000000000002 0000000000000000 
>        000000003b33bb80 000000003b33baf8 000000003b33baf8 00000000000175d6 
>        0000000000000001 000000003b33b988 000000003f9b0000 000000000000000b 
>        000000000000000c 000000003b33bb40 000000003b33bae0 0000000000000000 
>        0000000000000000 00000000000175d6 000000003b33bae0 000000003b33bb28 
> Call Trace:
> ([<00000000000174b2>] show_trace+0x112/0x170)
>  [<0000000000017582>] show_stack+0x72/0x100
>  [<0000000000441538>] dump_stack+0xc8/0xd8
>  [<000000000025c350>] debug_smp_processor_id+0x114/0x130
>  [<00000000000bf0e4>] trace_find_cmdline+0x40/0xfc
>  [<00000000000c35d4>] trace_print_context+0x58/0xac
>  [<00000000000bb676>] print_trace_line+0x416/0x470
>  [<00000000000bc8fe>] s_show+0x4e/0x428
>  [<000000000013834e>] seq_read+0x36a/0x5d4
>  [<0000000000112a78>] vfs_read+0xc8/0x174
>  [<0000000000112c58>] SyS_read+0x74/0xc4
>  [<000000000002c7ae>] sysc_noemu+0x10/0x16
>  [<000002000012436c>] 0x2000012436c
> 1 lock held by cat/2278:
>  #0:  (&p->lock){+.+.+.}, at: [<0000000000138056>] seq_read+0x72/0x5d4

Shouldn't that be preempt_disable_notrace() and co to avoid tracer
recursion?


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