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 | Fri, 2 Apr 2021 23:09:09 -0400 |
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On 4/2/21 4:40 PM, Steven Rostedt wrote: > On Thu, 1 Apr 2021 14:10:30 -0400 > Waiman Long <longman@redhat.com> wrote: > >> The handling of sysrq key can be activated by echoing the key to >> /proc/sysrq-trigger or via the magic key sequence typed into a terminal >> that is connected to the system in some way (serial, USB or other mean). >> In the former case, the handling is done in a user context. In the >> latter case, it is likely to be in an interrupt context. >> >> There should be no more than one instance of sysrq key processing via >> a terminal, but multiple instances of /proc/sysrq-trigger is possible. >> >> Currently in print_cpu() of kernel/sched/debug.c, sched_debug_lock is >> taken with interrupt disabled for the whole duration of the calls to >> print_*_stats() and print_rq() which could last for the quite some time >> if the information dump happens on the serial console. >> >> If the system has many cpus and the sched_debug_lock is somehow busy >> (e.g. parallel sysrq-t), the system may hit a hard lockup panic >> depending on the actually serial console implementation of the >> system. For instance, > Wouldn't placing strategically located "touch_nmi_watchdog()"s around fix > this? > > -- Steve > 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.
Cheers, Longman
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