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Subject[PATCH] workqueue: fix possible race condition when rescuer VS pwq-release
Date
There is a race condition between rescuer_thread() and
pwq_unbound_release_workfn().

The works of the @pwq may be processed by some other worker,
and @pwq is scheduled to release before the rescuer starts
to process. In this case pwq_unbound_release_workfn() will
corrupt wq->maydays, and rescuer_thead will access to corrupted
data.

Using get_pwq() when send_mayday() will keep @pwq's lifetime
and avoid the race condition.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
---
kernel/workqueue.c | 7 +++++++
1 files changed, 7 insertions(+), 0 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 82ef9f3..7066519 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -1902,6 +1902,12 @@ static void send_mayday(struct work_struct *work)

/* mayday mayday mayday */
if (list_empty(&pwq->mayday_node)) {
+ /*
+ * Keep the pwq and avoid the pwq to be scheduled to release
+ * when someone else processes all the works before the rescuer
+ * starts to process.
+ */
+ get_pwq(pwq);
list_add_tail(&pwq->mayday_node, &wq->maydays);
wake_up_process(wq->rescuer->task);
}
@@ -2418,6 +2424,7 @@ repeat:
/* migrate to the target cpu if possible */
worker_maybe_bind_and_lock(pool);
rescuer->pool = pool;
+ put_pwq(pwq);

/*
* Slurp in all works issued via this workqueue and
--
1.7.7.6


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