linux-kernel - Re: [PATCH] ASoC: fsl_asrc: Add reg_defaults for regmap to fix kernel dump

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Message-ID: <20141028001904.GH18557@sirena.org.uk>
Date:	Tue, 28 Oct 2014 00:19:04 +0000
From:	Mark Brown <broonie@...nel.org>
To:	Nicolin Chen <nicoleotsuka@...il.com>
Cc:	linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
	alsa-devel@...a-project.org
Subject: Re: [PATCH] ASoC: fsl_asrc: Add reg_defaults for regmap to fix
 kernel dump

On Fri, Oct 24, 2014 at 07:03:57PM -0700, Nicolin Chen wrote:
> Kernel dump (WARN_ON) ocurred during system boot-up inside regmap_write():
> 
> ------------[ cut here ]------------
> WARNING: CPU: 0 PID: 47 at kernel/locking/lockdep.c:2744 lockdep_trace_alloc+0xe8/0x108()

Applied, thanks.  Please edit down or elide backtraces - they take up a
lot of space in the changelog compared to the amount of information they
contain.

> By looking at 2744 line, we can get that it's because regcache_rbtree_write()
> would call kmalloc() with GFP flag if it couldn't find an existing block to
> insert nodes while this kmalloc() call is inside a spin_lock_irq_save pair,
> i.e. IRQs disabled.

> Even though this may be a bug that should be fixed, I still try to send this
> patch as a quick fix (work around) since it does no harm to assign default
> values of every registers when using regcache.

It's not a bug, it's not reasonable to default allocations to atomic and
we can't really tell what context we're in.  Anything used inside a
heavily locked path should either have a default provided or arrange for
a prior write to set up the cache.

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