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Date: Tue, 28 Apr 2020 16:40:26 +0200 From: Rasmus Villemoes <rasmus.villemoes@...vas.dk> To: linux-kernel@...r.kernel.org Cc: linux-rt-users@...r.kernel.org, Rasmus Villemoes <rasmus.villemoes@...vas.dk>, Steven Rostedt <rostedt@...dmis.org>, Thomas Gleixner <tglx@...utronix.de>, Carsten Emde <C.Emde@...dl.org>, Sebastian Andrzej Siewior <bigeasy@...utronix.de>, Tom Zanussi <zanussi@...nel.org>, Julien Grall <julien.grall@....com>, Daniel Wagner <wagi@...om.org>, John Kacur <jkacur@...hat.com> Subject: [PATCH -rt] hrtimer: fix logic for when grabbing softirq_expiry_lock can be elided Commit hrtimer: Add a missing bracket and hide `migration_base' on !SMP which is 47b6de0b7f22 in 5.2-rt and 40aae5708e7a in 4.19-rt, inadvertently changed the logic from base != &migration_base to base == &migration_base. On !CONFIG_SMP, the effect was to effectively always elide this lock/unlock pair (since is_migration_base() is unconditionally false), which for me consistently causes lockups during reboot, and reportedly also often causes a hang during boot. Adding this logical negation (or, what is effectively the same thing on !CONFIG_SMP, reverting the above commit as well as "hrtimer: Prevent using hrtimer_grab_expiry_lock() on migration_base") fixes that lockup. Fixes: 40aae5708e7a (hrtimer: Add a missing bracket and hide `migration_base' on !SMP) # 4.19-rt Fixes: 47b6de0b7f22 (hrtimer: Add a missing bracket and hide `migration_base' on !SMP) # 5.2-rt Signed-off-by: Rasmus Villemoes <rasmus.villemoes@...vas.dk> --- Something like this? I wasn't sure what Fixes: tag(s) to include, if any. It's quite possible the same fix is needed on earlier -rt kernels, I didn't check. kernel/time/hrtimer.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c index e54a95de8b79..c3966c090246 100644 --- a/kernel/time/hrtimer.c +++ b/kernel/time/hrtimer.c @@ -953,7 +953,7 @@ void hrtimer_grab_expiry_lock(const struct hrtimer *timer) { struct hrtimer_clock_base *base = READ_ONCE(timer->base); - if (timer->is_soft && is_migration_base(base)) { + if (timer->is_soft && !is_migration_base(base)) { spin_lock(&base->cpu_base->softirq_expiry_lock); spin_unlock(&base->cpu_base->softirq_expiry_lock); } -- 2.23.0
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