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Date: Wed, 23 Jan 2008 13:31:49 +0000 From: Pavel Machek <pavel@....cz> To: Steven Rostedt <rostedt@...dmis.org> Cc: LKML <linux-kernel@...r.kernel.org>, Linus Torvalds <torvalds@...ux-foundation.org>, Andrew Morton <akpm@...ux-foundation.org>, Alexey Dobriyan <adobriyan@...nvz.org>, Kirill Korotaev <dev@...ru> Subject: Re: [PATCH] printk deadlocks if called with runqueue lock held Hi! > I thought that one could place a printk anywhere without worrying. > But it seems that it is not wise to place a printk where the runqueue > lock is held. > > I just spent two hours debugging why some of my code was locking up, > to find that the lockup was caused by some debugging printk's that > I had in the scheduler. The printk's were only in rare paths so > they shouldn't be too much of a problem, but after I hit the printk > the system locked up. > > Thinking that it was locking up on my code I went looking down the > wrong path. I finally found (after examining an NMI dump) that > the lockup happened because printk was trying to wakeup the klogd > daemon, which caused a deadlock when the try_to_wakeup code tries > to grab the runqueue lock. Could try_to_wakeup use trylock, and only avoid wakeup if lock is already held? Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html -- 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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