From: Tejun Heo <tj@kernel.org>
Date: Wed, 23 Jan 2013 00:48:03 +0000 (-0800)
Subject: async, kmod: warn on synchronous request_module() from async workers
X-Git-Tag: v3.9-rc1~158^2~6
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=0fdff3ec6d87856cdcc99e69cf42143fdd6c56b4;p=pandora-kernel.git

async, kmod: warn on synchronous request_module() from async workers

Synchronous requet_module() from an async worker can lead to deadlock
because module init path may invoke async_synchronize_full().  The
async worker waits for request_module() to complete and the module
loading waits for the async task to finish.  This bug happened in the
block layer because of default elevator auto-loading.

Block layer has been updated not to do default elevator auto-loading
and it has been decided to disallow synchronous request_module() from
async workers.

Trigger WARN_ON_ONCE() on synchronous request_module() from async
workers.

For more details, please refer to the following thread.

  http://thread.gmane.org/gmane.linux.kernel/1420814

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Alex Riesen <raa.lkml@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Arjan van de Ven <arjan@linux.intel.com>
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