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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>
This commit is contained in:
Wu Fengguang 2012-02-04 20:54:03 -06:00
parent 3310225dfc
commit 977b7e3a52
1 changed files with 4 additions and 1 deletions
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5
include/trace/events/writeback.h
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@ -47,7 +47,10 @@ DECLARE_EVENT_CLASS(writeback_work_class,
__field(int, reason)
),
TP_fast_assign(
strncpy(__entry->name, dev_name(bdi->dev), 32);
struct device *dev = bdi->dev;
if (!dev)
dev = default_backing_dev_info.dev;
strncpy(__entry->name, dev_name(dev), 32);
__entry->nr_pages = work->nr_pages;
__entry->sb_dev = work->sb ? work->sb->s_dev : 0;
__entry->sync_mode = work->sync_mode;