From: Rasmus Villemoes Date: Tue, 28 Apr 2020 16:40:26 +0200 Subject: [PATCH 324/351] hrtimer: fix logic for when grabbing softirq_expiry_lock can be elided Origin: https://git.kernel.org/cgit/linux/kernel/git/rt/linux-stable-rt.git/commit?id=36b0eadf58daa2135f9139436ccfd778db315f0f 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 Reviewed-by: Steven Rostedt (VMware) Signed-off-by: Tom Zanussi --- 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 0f841f18c363..a84673149881 100644 --- a/kernel/time/hrtimer.c +++ b/kernel/time/hrtimer.c @@ -971,7 +971,7 @@ 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); }