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From: Peter Zijlstra <peterz@infradead.org>
To: Stefan Agner <stefan@agner.ch>
Cc: broonie@kernel.org, mingo@redhat.com,
	dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org
Subject: Re: Lockdep warning when using REGCACHE_RBTREE
Date: Fri, 15 Jan 2016 10:45:41 +0100	[thread overview]
Message-ID: <20160115094541.GH3421@worktop> (raw)
In-Reply-To: <afeb9e00e3082de585cfa458a0f47c56@agner.ch>

On Thu, Jan 14, 2016 at 02:30:50PM -0800, Stefan Agner wrote:
> Hi Mark,
> 
> I currently work on the DCU DRM driver (drivers/gpu/drm/fsl-dcu/) on a
> Linux 4.4 kernel. With CONFIG_LOCKDEP enabled I get the following
> warning on startup:
> 
> [    1.327284] ------------[ cut here ]------------
> [    1.332010] WARNING: CPU: 0 PID: 1 at kernel/locking/lockdep.c:2755 lockdep_trace_alloc+0x120/0x124()
> [    1.341358] DEBUG_LOCKS_WARN_ON(irqs_disabled_flags(flags))

> [    1.521744] [<80375308>] (_regmap_write) from [<80376760>] (regmap_write+0x48/0x68)
> [    1.535348] [<80376718>] (regmap_write) from [<803538e8>] (fsl_dcu_drm_crtc_create+0x98/0xe8)
> [    1.549824] [<80353850>] (fsl_dcu_drm_crtc_create) from [<80352df0>] (fsl_dcu_drm_modeset_init+0x5c/0xfc)


> The comment in __lockdep_trace_alloc says:
> "Oi! Can't be having __GFP_FS allocations with IRQs disabled.".

So _regmap_write() does: map->lock(map->lock_arg)

Which isn't very enlightening, since that can be a mutex or a spinlock,
the above strongly suggests spinlock though.

Looking at __regmap_init(), this seems to depend on:

  (bus && bus->fast_io) || config->fast_io

now, afaict, regmap_mmio is used in this case, which has .fast_io =
true.

So yeah, fail.
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WARNING: multiple messages have this Message-ID (diff)
From: Peter Zijlstra <peterz@infradead.org>
To: Stefan Agner <stefan@agner.ch>
Cc: broonie@kernel.org, festevam@gmail.com, mingo@redhat.com,
	linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org
Subject: Re: Lockdep warning when using REGCACHE_RBTREE
Date: Fri, 15 Jan 2016 10:45:41 +0100	[thread overview]
Message-ID: <20160115094541.GH3421@worktop> (raw)
In-Reply-To: <afeb9e00e3082de585cfa458a0f47c56@agner.ch>

On Thu, Jan 14, 2016 at 02:30:50PM -0800, Stefan Agner wrote:
> Hi Mark,
> 
> I currently work on the DCU DRM driver (drivers/gpu/drm/fsl-dcu/) on a
> Linux 4.4 kernel. With CONFIG_LOCKDEP enabled I get the following
> warning on startup:
> 
> [    1.327284] ------------[ cut here ]------------
> [    1.332010] WARNING: CPU: 0 PID: 1 at kernel/locking/lockdep.c:2755 lockdep_trace_alloc+0x120/0x124()
> [    1.341358] DEBUG_LOCKS_WARN_ON(irqs_disabled_flags(flags))

> [    1.521744] [<80375308>] (_regmap_write) from [<80376760>] (regmap_write+0x48/0x68)
> [    1.535348] [<80376718>] (regmap_write) from [<803538e8>] (fsl_dcu_drm_crtc_create+0x98/0xe8)
> [    1.549824] [<80353850>] (fsl_dcu_drm_crtc_create) from [<80352df0>] (fsl_dcu_drm_modeset_init+0x5c/0xfc)


> The comment in __lockdep_trace_alloc says:
> "Oi! Can't be having __GFP_FS allocations with IRQs disabled.".

So _regmap_write() does: map->lock(map->lock_arg)

Which isn't very enlightening, since that can be a mutex or a spinlock,
the above strongly suggests spinlock though.

Looking at __regmap_init(), this seems to depend on:

  (bus && bus->fast_io) || config->fast_io

now, afaict, regmap_mmio is used in this case, which has .fast_io =
true.

So yeah, fail.

  parent reply	other threads:[~2016-01-15  9:45 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-01-14 22:30 Lockdep warning when using REGCACHE_RBTREE Stefan Agner
2016-01-14 22:30 ` Stefan Agner
2016-01-15  0:01 ` Mark Brown
2016-01-15  1:14   ` Stefan Agner
2016-01-15  1:14     ` Stefan Agner
2016-01-15 16:28     ` Mark Brown
2016-01-15 16:28       ` Mark Brown
2016-01-15 19:08       ` Stefan Agner
2016-01-15 19:08         ` Stefan Agner
2016-01-15  9:45 ` Peter Zijlstra [this message]
2016-01-15  9:45   ` Peter Zijlstra
2016-01-15 11:49   ` Mark Brown
2016-01-15 11:49     ` Mark Brown

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