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authorTejun Heo <tj@kernel.org>2012-08-13 17:08:19 -0700
committerTejun Heo <tj@kernel.org>2012-08-13 17:08:19 -0700
commit23657bb192f14b789e4c478def8f11ecc95b4f6c (patch)
tree53d92c542c219d60ccef2ada045235f5e7076863 /kernel/workqueue.c
parent1265057fa02c7bed3b6d9ddc8a2048065a370364 (diff)
downloadop-kernel-dev-23657bb192f14b789e4c478def8f11ecc95b4f6c.zip
op-kernel-dev-23657bb192f14b789e4c478def8f11ecc95b4f6c.tar.gz
workqueue: add missing wmb() in clear_work_data()
Any operation which clears PENDING should be preceded by a wmb to guarantee that the next PENDING owner sees all the changes made before PENDING release. There are only two places where PENDING is cleared - set_work_cpu_and_clear_pending() and clear_work_data(). The caller of the former already does smp_wmb() but the latter doesn't have any. Move the wmb above set_work_cpu_and_clear_pending() into it and add one to clear_work_data(). There hasn't been any report related to this issue, and, given how clear_work_data() is used, it is extremely unlikely to have caused any actual problems on any architecture. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Oleg Nesterov <oleg@redhat.com>
Diffstat (limited to 'kernel/workqueue.c')
-rw-r--r--kernel/workqueue.c19
1 files changed, 12 insertions, 7 deletions
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 11723c5..4fef952 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -570,11 +570,19 @@ static void set_work_cwq(struct work_struct *work,
static void set_work_cpu_and_clear_pending(struct work_struct *work,
unsigned int cpu)
{
+ /*
+ * The following wmb is paired with the implied mb in
+ * test_and_set_bit(PENDING) and ensures all updates to @work made
+ * here are visible to and precede any updates by the next PENDING
+ * owner.
+ */
+ smp_wmb();
set_work_data(work, (unsigned long)cpu << WORK_OFFQ_CPU_SHIFT, 0);
}
static void clear_work_data(struct work_struct *work)
{
+ smp_wmb(); /* see set_work_cpu_and_clear_pending() */
set_work_data(work, WORK_STRUCT_NO_CPU, 0);
}
@@ -2182,14 +2190,11 @@ __acquires(&gcwq->lock)
wake_up_worker(pool);
/*
- * Record the last CPU and clear PENDING. The following wmb is
- * paired with the implied mb in test_and_set_bit(PENDING) and
- * ensures all updates to @work made here are visible to and
- * precede any updates by the next PENDING owner. Also, clear
- * PENDING inside @gcwq->lock so that PENDING and queued state
- * changes happen together while IRQ is disabled.
+ * Record the last CPU and clear PENDING which should be the last
+ * update to @work. Also, do this inside @gcwq->lock so that
+ * PENDING and queued state changes happen together while IRQ is
+ * disabled.
*/
- smp_wmb();
set_work_cpu_and_clear_pending(work, gcwq->cpu);
spin_unlock_irq(&gcwq->lock);
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