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backing-dev: fix wakeup timer races with bdi_unregister() 

While 7a401a972d ("backing-dev: ensure wakeup_timer is deleted")
addressed the problem of the bdi being freed with a queued wakeup
timer, there are other races that could happen if the wakeup timer
expires after/during bdi_unregister(), before bdi_destroy() is called.

wakeup_timer_fn() could attempt to wakeup a task which has already has
been freed, or could access a NULL bdi->dev via the wake_forker_thread
tracepoint.

Cc: <stable@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Reported-by: Chanho Min <chanho.min@lge.com>
Reviewed-by: Namjae Jeon <linkinjeon@gmail.com>
Signed-off-by: Rabin Vincent <rabin@rab.in>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
hifive-unleashed-5.1
Rabin Vincent 2012-01-29 12:17:33 -06:00 committed by Wu Fengguang
parent 62aa2b537c
commit 2673b4cf5d
1 changed files with 18 additions and 5 deletions
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23
mm/backing-dev.c
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@ -318,7 +318,7 @@ static void wakeup_timer_fn(unsigned long data)
if (bdi->wb.task) {
trace_writeback_wake_thread(bdi);
wake_up_process(bdi->wb.task);
} else {
} else if (bdi->dev) {
/*
* When bdi tasks are inactive for long time, they are killed.
* In this case we have to wake-up the forker thread which
@ -584,6 +584,8 @@ EXPORT_SYMBOL(bdi_register_dev);
*/
static void bdi_wb_shutdown(struct backing_dev_info *bdi)
{
struct task_struct *task;
if (!bdi_cap_writeback_dirty(bdi))
return;
@ -602,8 +604,13 @@ static void bdi_wb_shutdown(struct backing_dev_info *bdi)
* Finally, kill the kernel thread. We don't need to be RCU
* safe anymore, since the bdi is gone from visibility.
*/
if (bdi->wb.task)
kthread_stop(bdi->wb.task);
spin_lock_bh(&bdi->wb_lock);
task = bdi->wb.task;
bdi->wb.task = NULL;
spin_unlock_bh(&bdi->wb_lock);
if (task)
kthread_stop(task);
}
/*
@ -623,7 +630,9 @@ static void bdi_prune_sb(struct backing_dev_info *bdi)
void bdi_unregister(struct backing_dev_info *bdi)
{
if (bdi->dev) {
struct device *dev = bdi->dev;
if (dev) {
bdi_set_min_ratio(bdi, 0);
trace_writeback_bdi_unregister(bdi);
bdi_prune_sb(bdi);
@ -632,8 +641,12 @@ void bdi_unregister(struct backing_dev_info *bdi)
if (!bdi_cap_flush_forker(bdi))
bdi_wb_shutdown(bdi);
bdi_debug_unregister(bdi);
device_unregister(bdi->dev);
spin_lock_bh(&bdi->wb_lock);
bdi->dev = NULL;
spin_unlock_bh(&bdi->wb_lock);
device_unregister(dev);
}
}
EXPORT_SYMBOL(bdi_unregister);