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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Sat, 22 Jun 2019 00:09:22 +0200
Subject: [PATCH] softirq: Avoid a cancel dead-lock in tasklet handling due to
preemptible-softirq
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/5.2/older/patches-5.2.17-rt9.tar.xz
A pending / active tasklet which is preempted by a task on the same CPU
will spin indefinitely becauase the tasklet makes no progress.
To avoid this deadlock we can disable BH which will acquire the
softirq-lock which will force the completion of the softirq and so the
tasklet.
The BH off/on in tasklet_kill() will force tasklets which are not yet
running but scheduled (because ksoftirqd was preempted before it could
start the tasklet).
The BH off/on in tasklet_unlock_wait() will force tasklets which got
preempted while running.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
include/linux/interrupt.h | 5 ++++-
kernel/softirq.c | 3 ++-
2 files changed, 6 insertions(+), 2 deletions(-)
--- a/include/linux/interrupt.h
+++ b/include/linux/interrupt.h
@@ -625,7 +625,10 @@ static inline void tasklet_unlock(struct
static inline void tasklet_unlock_wait(struct tasklet_struct *t)
{
- while (test_bit(TASKLET_STATE_RUN, &(t)->state)) { barrier(); }
+ while (test_bit(TASKLET_STATE_RUN, &(t)->state)) {
+ local_bh_disable();
+ local_bh_enable();
+ }
}
#else
#define tasklet_trylock(t) 1
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -711,7 +711,8 @@ void tasklet_kill(struct tasklet_struct
while (test_and_set_bit(TASKLET_STATE_SCHED, &t->state)) {
do {
- yield();
+ local_bh_disable();
+ local_bh_enable();
} while (test_bit(TASKLET_STATE_SCHED, &t->state));
}
tasklet_unlock_wait(t);
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