From: Tom Zanussi Date: Tue, 9 Jun 2020 11:04:08 -0500 Subject: [PATCH 327/353] tasklet: Fix UP case for tasklet CHAINED state Origin: https://git.kernel.org/cgit/linux/kernel/git/rt/linux-stable-rt.git/commit?id=73881f36e14be59b92716efa0b760ccadfd3d80a 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 Reported-by: Ramon Fried Tested-By: Ramon Fried --- 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: */