Messages in this thread | | | Subject | Re: [PATCH v3] sched/debug: Use sched_debug_lock to serialize use of cgroup_path[] only | From | Waiman Long <> | Date | Sun, 4 Apr 2021 21:29:43 -0400 |
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On 4/4/21 9:27 PM, Waiman Long wrote: > On 4/4/21 12:02 PM, Steven Rostedt wrote: >> On Fri, 2 Apr 2021 23:09:09 -0400 >> Waiman Long <longman@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(). > > Thanks for the suggestion, but it also sound complicated. > > I think we can fix this lockup problem if we are willing to lose some > information in case of contention. As you have suggested, a trylock > will be used to acquire sched_debug_lock. If succeeded, all is good. > Otherwise, a shorter stack buffer will be used for cgroup path. The > path may be truncated in this case. If we detect that the full length > of the buffer is used, we assume truncation and add, e.g. "...", to > indicate there is more to the actual path. > > Do you think this is an acceptable comprise?
Actually, I don't really need to disable interrupt under this situation as deadlock can't happen.
Cheers, Longman
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