[PATCH] mm/backing-dev.c: fix crash when USB/SCSI device is detached

[민찬호 <chanho.min@lge.com>]

from Chanho Min <chanho.min@lge.com>

System may crash in backing-dev.c when removal SCSI device is detached.
bdi task is killed by bdi_unregister()/'khubd', but task's point remains.
Shortly afterward, If 'wb->wakeup_timer' is expired before
del_timer()/bdi_forker_thread,
wakeup_timer_fn() may wake up the dead thread which cause the crash.
'bdi->wb.task' should be NULL as this patch.

Signed-off-by: Chanho Min <chanho.min@lge.com>
---
 mm/backing-dev.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 71034f4..4378a5e 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -607,6 +607,7 @@ static void bdi_wb_shutdown(struct backing_dev_info
*bdi)
        if (bdi->wb.task) {
                thaw_process(bdi->wb.task);
                kthread_stop(bdi->wb.task);
+               bdi->wb.task = NULL;
        }
 }

-- 
1.7.0.4

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