thread on sleepqueue does not wake up after timeout
Konstantin Belousov
kostikbel at gmail.com
Tue Oct 22 10:44:43 UTC 2019
On Tue, Oct 22, 2019 at 01:08:59PM +0300, Andriy Gapon wrote:
>
> We observe a problem that happens very rarely (about once a month across many
> test machines). The problem is that a thread remain in sleepq_timedwait() even
> after its timeout expires. The thread's td_slpcallout looks like the callout
> has fired. But the thread's state looks like it was never notified.
> E.g.:
> (kgdb) p td->td_slpcallout
> $1 = {c_links = {le = {le_next = 0xfffff800108e6470, le_prev =
> 0xfffffe0000be6ea8}, sle = {sle_next = 0xfffff800108e6470}, tqe = {tqe_next =
> 0xfffff800108e6470, tqe_prev = 0xfffffe0000be6ea8}}, c_time = 160957479343159,
> c_precision = 268435450, c_arg = 0xfffff80184602000, c_func =
> 0xffffffff807481d0 <sleepq_timeout>, c_lock = 0x0, c_flags = 2, c_iflags = 272,
> c_cpu = 6, c_exec_time = 160957506517070} [*]
> (kgdb) p/x td->td_flags
> $5 = 0x80000004
What is the bit 31 in your flags ? FreeBSD does not use the bit.
> (kgdb) p td->td_sqqueue
> $8 = 0
> (kgdb) p td->td_sleepqueue
> $9 = (struct sleepqueue *) 0x0
> (kgdb) p td->td_wchan
> $10 = (void *) 0xfffff802b990df38
>
>
> Has anyone seen anything like this problem?
Yes, but it was very long time ago. See r303426.
> Any advice on how to diagnose it?
>
> Thanks!
>
> P.S.
> c_exec_time is our addition, we set this field right before firing a callback
> and we reset it to zero when a callout is (re-)scheduled.
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