linux-kernel - INPUT: leds trigger LOCKDEP (GFP

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Message-ID: <4C061715.5060700@gmail.com>
Date:	Wed, 02 Jun 2010 10:32:21 +0200
From:	Jiri Slaby <jirislaby@...il.com>
To:	rpurdie@...ys.net
CC:	linux-input@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: INPUT: leds trigger LOCKDEP (GFP_KERNEL alloc inside spinlock)

Hi,

I get the following warning when booting with lockdep turned on:
------------[ cut here ]------------
WARNING: at kernel/lockdep.c:2469 lockdep_trace_alloc+0xbc/0xd0()
Hardware name: Bochs
Modules linked in:
Pid: 1, comm: swapper Not tainted 2.6.34-mm1_64+ #5
Call Trace:
 [<ffffffff8106408a>] warn_slowpath_common+0x7a/0xb0
 [<ffffffff81324826>] ? device_create_vargs+0x56/0x110
 [<ffffffff810640d5>] warn_slowpath_null+0x15/0x20
 [<ffffffff8109359c>] lockdep_trace_alloc+0xbc/0xd0
 [<ffffffff810f65b2>] kmem_cache_alloc+0x32/0xf0
 [<ffffffff81324826>] device_create_vargs+0x56/0x110
 [<ffffffff8132490c>] device_create+0x2c/0x30
 [<ffffffff810828ce>] ? up_read+0x1e/0x40
 [<ffffffff8142068c>] led_classdev_register+0x2c/0xe0
 [<ffffffff814213de>] input_led_connect+0x21e/0x2c0
 [<ffffffff813d2395>] ? input_register_handler+0x25/0x110
 [<ffffffff813cfd87>] input_attach_handler+0x1c7/0x210
 [<ffffffff81abc666>] ? input_led_init+0x0/0x12
 [<ffffffff813d2433>] input_register_handler+0xc3/0x110
 [<ffffffff81abc666>] ? input_led_init+0x0/0x12
 [<ffffffff81abc676>] input_led_init+0x10/0x12
 [<ffffffff810002f9>] do_one_initcall+0x39/0x1a0
 [<ffffffff81a95d83>] kernel_init+0x16e/0x1f8
 [<ffffffff8102ab14>] kernel_thread_helper+0x4/0x10
 [<ffffffff8159917c>] ? restore_args+0x0/0x30
 [<ffffffff81a95c15>] ? kernel_init+0x0/0x1f8
 [<ffffffff8102ab10>] ? kernel_thread_helper+0x0/0x10
---[ end trace e7273345439c18af ]---
Registered led device: input::numl


It is because input_led_connect makes an atomic context and calls from
that led_classdev_register. In this function there are several functions
which might sleep, so this is incorrect.

Is it necessary that input_led_registered_lock is a spinlock? Can't it
be simply a mutex?

regards,
-- 
js
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