On 2020-12-06 22:40:07 [+0100], Thomas Gleixner wrote: > syzbot reported KCSAN data races vs. timer_base::timer_running being set to > NULL without holding base::lock in expire_timers(). > > This looks innocent and most reads are clearly not problematic but for a > non-RT kernel it's completely irrelevant whether the store happens before > or after taking the lock. For an RT kernel moving the store under the lock > requires an extra unlock/lock pair in the case that there is a waiter for > the timer. But that's not the end of the world and definitely not worth the > trouble of adding boatloads of comments and annotations to the code. Famous > last words... > > Reported-by: syzbot+aa7c2385d46c5eba0...@syzkaller.appspotmail.com > Reported-by: syzbot+abea4558531bae1ba...@syzkaller.appspotmail.com > Signed-off-by: Thomas Gleixner <t...@linutronix.de>
One thing I noticed while testing it is that the "corner" case in timer_sync_wait_running() is quite reliably hit by rcu_preempt rcu_gp_fqs_loop() -> swait_event_idle_timeout_exclusive() invocation. Sebastian
