6.17-stable review patch. If anyone has any objections, please let me know.
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From: Sebastian Andrzej Siewior bigeasy@linutronix.de
[ Upstream commit 9fc4a3da9a0259a0500848b5d8657918efde176b ]
snd_pcm_group_lock_irq() acquires a spinlock_t and disables interrupts via spin_lock_irq(). This also implicitly disables the handling of softirqs such as TIMER_SOFTIRQ. On PREEMPT_RT softirqs are preemptible and spin_lock_irq() does not disable them. That means a timer can be invoked during spin_lock_irq() on the same CPU. Due to synchronisations reasons local_bh_disable() has a per-CPU lock named softirq_ctrl.lock which synchronizes individual softirq against each other. syz-bot managed to trigger a lockdep report where softirq_ctrl.lock is acquired in hrtimer_cancel() in addition to hrtimer_run_softirq(). This is a possible deadlock.
The softirq_ctrl.lock can not be made part of spin_lock_irq() as this would lead to too much synchronisation against individual threads on the system. To avoid the possible deadlock, softirqs must be manually disabled before the lock is acquired.
Disable softirqs before the lock is acquired on PREEMPT_RT.
Reported-by: syzbot+10b4363fb0f46527f3f3@syzkaller.appspotmail.com Fixes: d2d6422f8bd1 ("x86: Allow to enable PREEMPT_RT.") Signed-off-by: Sebastian Andrzej Siewior bigeasy@linutronix.de Signed-off-by: Takashi Iwai tiwai@suse.de Signed-off-by: Sasha Levin sashal@kernel.org --- sound/core/pcm_native.c | 25 +++++++++++++++---------- 1 file changed, 15 insertions(+), 10 deletions(-)
diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c index 1eab940fa2e5a..68bee40c9adaf 100644 --- a/sound/core/pcm_native.c +++ b/sound/core/pcm_native.c @@ -84,19 +84,24 @@ void snd_pcm_group_init(struct snd_pcm_group *group) }
/* define group lock helpers */ -#define DEFINE_PCM_GROUP_LOCK(action, mutex_action) \ +#define DEFINE_PCM_GROUP_LOCK(action, bh_lock, bh_unlock, mutex_action) \ static void snd_pcm_group_ ## action(struct snd_pcm_group *group, bool nonatomic) \ { \ - if (nonatomic) \ + if (nonatomic) { \ mutex_ ## mutex_action(&group->mutex); \ - else \ - spin_ ## action(&group->lock); \ -} - -DEFINE_PCM_GROUP_LOCK(lock, lock); -DEFINE_PCM_GROUP_LOCK(unlock, unlock); -DEFINE_PCM_GROUP_LOCK(lock_irq, lock); -DEFINE_PCM_GROUP_LOCK(unlock_irq, unlock); + } else { \ + if (IS_ENABLED(CONFIG_PREEMPT_RT) && bh_lock) \ + local_bh_disable(); \ + spin_ ## action(&group->lock); \ + if (IS_ENABLED(CONFIG_PREEMPT_RT) && bh_unlock) \ + local_bh_enable(); \ + } \ +} + +DEFINE_PCM_GROUP_LOCK(lock, false, false, lock); +DEFINE_PCM_GROUP_LOCK(unlock, false, false, unlock); +DEFINE_PCM_GROUP_LOCK(lock_irq, true, false, lock); +DEFINE_PCM_GROUP_LOCK(unlock_irq, false, true, unlock);
/** * snd_pcm_stream_lock - Lock the PCM stream