linux-kernel - Re: Deadlock in do_page_fault() on ARM (old kernel)

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Message-ID: <20140117134646.GL27282@n2100.arm.linux.org.uk>
Date:	Fri, 17 Jan 2014 13:46:46 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Alan Ott <alan@...nal11.us>
Cc:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-omap@...r.kernel.org
Subject: Re: Deadlock in do_page_fault() on ARM (old kernel)

On Wed, Jan 15, 2014 at 08:13:04PM -0500, Alan Ott wrote:
> So my questions are:
> 1. Why don't I see a full backtrace beyond the exception stack? It's the  
> same when dump_stack() is called manually.

No idea - it looks like you're not using frame pointers, but are using
the unwinder.  Full backtraces can always be created with frame pointers,
it's just that unwinding seems unreliable.

I think we do need to see the full backtrace here - from looking at the
full state dump, I don't see any sign of the mmap_sem being held except
by an attempt to process a fault, and two threads trying to do a
sys_mmap_pgoff().

My suspicion therefore is that some other thread must have died while
holding the mmap_sem, so there's probably a kernel oops earlier...
that's my best guess at the moment without seeing the full backtrace.

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