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Message-ID: <4511008E.5090005@linux.intel.com>
Date: Wed, 20 Sep 2006 16:49:18 +0800
From: Arjan van de Ven <arjan@linux.intel.com>
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To: Ingo Molnar <mingo@elte.hu>
CC: Peter Zijlstra <a.p.zijlstra@chello.nl>,
       linux-kernel <linux-kernel@vger.kernel.org>,
       Andrew Morton <akpm@osdl.org>
Subject: Re: [PATCH] rtc: lockdep fix
References: <1158695676.28174.21.camel@lappy> <20060920082135.GB12517@elte.hu>
In-Reply-To: <20060920082135.GB12517@elte.hu>
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Ingo Molnar wrote:
> * Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:
> 
>> BUG: warning at kernel/lockdep.c:1816/trace_hardirqs_on() (Not tainted)
>>  [<c04051ee>] show_trace_log_lvl+0x58/0x171
>>  [<c0405802>] show_trace+0xd/0x10
>>  [<c040591b>] dump_stack+0x19/0x1b
>>  [<c043abee>] trace_hardirqs_on+0xa2/0x11e
>>  [<c06143c3>] _spin_unlock_irq+0x22/0x26
>>  [<c0541540>] rtc_get_rtc_time+0x32/0x176
>>  [<c0419ba4>] hpet_rtc_interrupt+0x92/0x14d
>>  [<c0450f94>] handle_IRQ_event+0x20/0x4d
>>  [<c0451055>] __do_IRQ+0x94/0xef
>>  [<c040678d>] do_IRQ+0x9e/0xbd
>>  [<c0404a49>] common_interrupt+0x25/0x2c
> 
> ouch! That is a scenario that could lead to real lockups. Fix looks good 
> and necessary for v2.6.18 to me.
> 

btw this entire code path is evil; the rtc_get_rtc_time() function can do really long delays
which is unsuitable for being called in interrupt context!
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