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From: Tom Zanussi <zanussi@kernel.org>
Date: Tue, 9 Jun 2020 11:04:08 -0500
Subject: [PATCH 327/351] tasklet: Fix UP case for tasklet CHAINED state
Origin: https://git.kernel.org/cgit/linux/kernel/git/rt/linux-stable-rt.git/commit?id=0d2b462527f8c10c0c852efeda88dd2cef218261
commit 62d0a2a30cd0 (tasklet: Address a race resulting in
double-enqueue) addresses a problem that can result in a tasklet being
enqueued on two cpus at the same time by combining the RUN flag with a
new CHAINED flag, and relies on the combination to be present in order
to zero it out, which can never happen on (!SMP and !PREEMPT_RT_FULL)
because the RUN flag is SMP/PREEMPT_RT_FULL-only.
So make sure the above commit is only applied for the SMP ||
PREEMPT_RT_FULL case.
Fixes: 62d0a2a30cd0 ("tasklet: Address a race resulting in double-enqueue")
Signed-off-by: Tom Zanussi <zanussi@kernel.org>
Reported-by: Ramon Fried <rfried.dev@gmail.com>
Tested-By: Ramon Fried <rfried.dev@gmail.com>
---
kernel/softirq.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/kernel/softirq.c b/kernel/softirq.c
index 73dae64bfc9c..9bad7a16dc61 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -947,10 +947,12 @@ static void __tasklet_schedule_common(struct tasklet_struct *t,
* is locked before adding it to the list.
*/
if (test_bit(TASKLET_STATE_SCHED, &t->state)) {
+#if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RT_FULL)
if (test_and_set_bit(TASKLET_STATE_CHAINED, &t->state)) {
tasklet_unlock(t);
return;
}
+#endif
t->next = NULL;
*head->tail = t;
head->tail = &(t->next);
@@ -1044,7 +1046,11 @@ static void tasklet_action_common(struct softirq_action *a,
again:
t->func(t->data);
+#if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RT_FULL)
while (cmpxchg(&t->state, TASKLET_STATEF_RC, 0) != TASKLET_STATEF_RC) {
+#else
+ while (!tasklet_tryunlock(t)) {
+#endif
/*
* If it got disabled meanwhile, bail out:
*/
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