On Fri, 2 Apr 2021 23:09:09 -0400 Waiman Long <long...@redhat.com> wrote:
> The main problem with sched_debug_lock is that under certain > circumstances, a lock waiter may wait a long time to acquire the lock > (in seconds). We can't insert touch_nmi_watchdog() while the cpu is > waiting for the spinlock. The problem I have with the patch is that it seems to be a hack (as it doesn't fix the issue in all cases). Since sched_debug_lock is "special", perhaps we can add wrappers to take it, and instead of doing the spin_lock_irqsave(), do a trylock loop. Add lockdep annotation to tell lockdep that this is not a try lock (so that it can still detect deadlocks). Then have the strategically placed touch_nmi_watchdog() also increment a counter. Then in that trylock loop, if it sees the counter get incremented, it knows that forward progress is being made by the lock holder, and it too can call touch_nmi_watchdog(). -- Steve
