From: Wu Fengguang <fengguang.wu@intel.com>
Date: Sun, 5 Feb 2012 02:54:03 +0000 (-0600)
Subject: writeback: fix dereferencing NULL bdi->dev on trace_writeback_queue
X-Git-Tag: v3.3-rc4~36^2
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=977b7e3a52a7421ad33a393a38ece59f3d41c2fa;p=pandora-kernel.git

writeback: fix dereferencing NULL bdi->dev on trace_writeback_queue

When a SD card is hot removed without umount, del_gendisk() will call
bdi_unregister() without destroying/freeing it. This leaves the bdi in
the bdi->dev = NULL, bdi->wb.task = NULL, bdi->bdi_list removed state.

When sync(2) gets the bdi before bdi_unregister() and calls
bdi_queue_work() after the unregister, trace_writeback_queue will be
dereferencing the NULL bdi->dev. Fix it with a simple test for NULL.

LKML-reference: http://lkml.org/lkml/2012/1/18/346
Cc: stable@kernel.org
Reported-by: Rabin Vincent <rabin@rab.in>
Tested-by: Namjae Jeon <linkinjeon@gmail.com>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
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