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Date: Tue, 08 Feb 2011 17:55:27 +0100 From: Peter Zijlstra <peterz@...radead.org> To: Yong Zhang <yong.zhang0@...il.com> Cc: Nick Bowler <nbowler@...iptictech.com>, linux-kernel@...r.kernel.org, Andrew Morton <akpm@...ux-foundation.org>, Thomas Gleixner <tglx@...utronix.de>, Steven Rostedt <rostedt@...dmis.org> Subject: Re: Regression: WARNINGS and lockdep spews in 2.6.38-rc3+ (bisected). On Thu, 2011-02-03 at 19:42 +0800, Yong Zhang wrote: > My patch is inspired by this http://lkml.org/lkml/2010/8/16/291 Right, so that splat warns about: spin_lock_irqsave(&shost->host_lock); del_timer_sync() spin_lock_irqsave(&t->split_timeout_timer); vs <SOFTIRQ> call_timer_fn() spin_lock(&t->split_timeout_timer); <IRQ> spin_lock_irqsave(&shost->host_lock); Which Steven just pointed out is an actual deadlock because: CPU0 CPU1 spin_lock_irqsave(&shost->host_lock); <SOFTIRQ> call_timer_fn(); base->running_timer = timer; func(); <IRQ> spin_lock(&shost->host_lock); del_timer_sync() while(base->running_timer == timer); And the world stops turning.. Also note that your patch changes the above to: spin_lock_irqsave(&shost->host_lock); del_timer_sync() spin_lock_bh(&t->split_timeout_timer); Which wouldn't make one bit of difference. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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