tjh.dev / kernel
Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
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tracing: Have osnoise_main() add a quiescent state for task rcu

ftracetest triggered:

INFO: rcu_tasks detected stalls on tasks:
00000000b92b832d: .. nvcsw: 1/1 holdout: 1 idle_cpu: -1/7
task:osnoise/7 state:R running task stack: 0 pid: 2133 ppid: 2 flags:0x00004000
Call Trace:
? asm_sysvec_apic_timer_interrupt+0x12/0x20
? asm_sysvec_apic_timer_interrupt+0x12/0x20
? trace_hardirqs_on+0x2b/0xe0
? asm_sysvec_apic_timer_interrupt+0x12/0x20
? trace_clock_local+0xc/0x20
? osnoise_main+0x10e/0x450
? trace_softirq_entry_callback+0x50/0x50
? kthread+0x153/0x170
? __kthread_bind_mask+0x60/0x60
? ret_from_fork+0x22/0x30

While running osnoise tracer with other tracers that rely on
synchronize_rcu_tasks(), where that just hung.

The reason is that osnoise_main() never schedules out if the interval
is less than 1, and this will cause synchronize_rcu_tasks() to never
return.

Link: https://lkml.kernel.org/r/20210628114953.6dc06a91@oasis.local.home

Fixes: bce29ac9ce0bb ("trace: Add osnoise tracer")
Acked-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Daniel Bristot de Oliveira <bristot@redhat.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

Steven Rostedt (VMware) b96285e1 6a2cbc58

+4 -1
+4 -1
kernel/trace/trace_osnoise.c
··· 1216 1216 * differently from hwlat_detector, the osnoise tracer can run 1217 1217 * without a pause because preemption is on. 1218 1218 */ 1219 - if (interval < 1) 1219 + if (interval < 1) { 1220 + /* Let synchronize_rcu_tasks() make progress */ 1221 + cond_resched_tasks_rcu_qs(); 1220 1222 continue; 1223 + } 1221 1224 1222 1225 if (msleep_interruptible(interval)) 1223 1226 break;