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authorRabin Vincent <rabin@rab.in>2012-01-29 12:17:33 -0600
committerWu Fengguang <fengguang.wu@intel.com>2012-02-01 16:52:49 +0800
commit2673b4cf5d59c3ee5e0c12f6d734d38770324dc4 (patch)
treeabef3ab4517f06b629f5dc4c516c135165cf7d81 /mm/backing-dev.c
parent62aa2b537c6f5957afd98e29f96897419ed5ebab (diff)
downloadlinux-2673b4cf5d59c3ee5e0c12f6d734d38770324dc4.tar.gz
backing-dev: fix wakeup timer races with bdi_unregister()
While 7a401a972df8e18 ("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>
Diffstat (limited to 'mm/backing-dev.c')
-rw-r--r--mm/backing-dev.c23
1 files changed, 18 insertions, 5 deletions
diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 7ba8feae11b..dd8e2aafb07 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -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);