Messages in this thread Patch in this message | | | Date | Wed, 01 Jun 2005 14:05:18 -0400 | From | john cooper <> | Subject | Re: RT and Cascade interrupts |
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Oleg Nesterov wrote: > This all is very unlikely of course, but it would be nice to verify > that kernel/timer.c is not the source of the problem.
The problem I am seeing is on a single CPU system.
> John, if it is easy to reproduce the problem, could you please retest > with this patch?
I've done so and the second assert is generated when running the test. So here we have a case of RPC_TASK_HAS_TIMER set but the associated timer->base == NULL. It would seem this could easily be the scenario of executing in:
__run_timers() timer->base = NULL; rpc_run_timer() task->tk_timeout_fn(task) /* ksoftirqd preempted */ : /* RPC client */ rpc_execute() rpc_delete_timer() del_timer() returns 0 BUG_ON(test_bit(RPC_TASK_HAS_TIMER, &task->tk_runstate)); : /* rpc_run_timer() resumes */ clear_bit(RPC_TASK_HAS_TIMER, &task->tk_runstate);
I don't see how this would imply a kernel/timer.c problem. It also appears this wouldn't be causing the timer cascade corruption I've seen as the end result is deleting an already dequeued timer which is safe here.
BTW, if preemption is explicitly disabled in rpc_run_timer() the BUG_ON assert is not generated nor (as reported earlier) does the cascade corruption occur. I'm still investigating.
-john
> --- 2.6.12-rc5/net/sunrpc/sched.c~ Wed Jun 1 17:49:57 2005 > +++ 2.6.12-rc5/net/sunrpc/sched.c Wed Jun 1 18:00:31 2005 > @@ -137,8 +137,12 @@ rpc_delete_timer(struct rpc_task *task) > { > if (RPC_IS_QUEUED(task)) > return; > - if (test_and_clear_bit(RPC_TASK_HAS_TIMER, &task->tk_runstate)) { > - del_singleshot_timer_sync(&task->tk_timer); > + if (test_bit(RPC_TASK_HAS_TIMER, &task->tk_runstate)) { > + if (del_singleshot_timer_sync(&task->tk_timer)) { > + BUG_ON(!test_bit(RPC_TASK_HAS_TIMER, &task->tk_runstate)); > + clear_bit(RPC_TASK_HAS_TIMER, &task->tk_runstate); > + } else > + BUG_ON(test_bit(RPC_TASK_HAS_TIMER, &task->tk_runstate)); > dprintk("RPC: %4d deleting timer\n", task->tk_pid); > } > } >
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