svn commit: r234952 - in head/sys: kern sys
Attilio Rao
attilio at freebsd.org
Thu May 3 11:02:11 UTC 2012
2012/5/3, Konstantin Belousov <kib at freebsd.org>:
> Author: kib
> Date: Thu May 3 10:38:02 2012
> New Revision: 234952
> URL: http://svn.freebsd.org/changeset/base/234952
>
> Log:
> When callout_reset_on() cannot immediately migrate a callout since it
> is running on other cpu, the CALLOUT_PENDING flag is temporarily
> cleared. Then, callout_stop() on this, in fact active, callout fails
> because CALLOUT_PENDING is not set, and callout_stop() returns 0.
>
> Now, in sleepq_check_timeout(), the failed callout_stop() causes the
> sleepq code to execute mi_switch() without even setting the wmesg,
> since the switch-out is supposed to be transient. In fact, the thread
> is put off the CPU for full timeout interval, instead of being put on
> runq immediately. Until timeout fires, the process is unkillable for
> obvious reasons.
>
> Fix this by marking the migrating callouts with CALLOUT_DFRMIGRATION
> flag. The flag is cleared by callout_stop_safe() when the function
> detects a migration, besides returning the success. The softclock()
> rechecks the flag for migrating callout and cancels its execution if
> the flag was cleared meantime.
Can you please clarify why you cannot simply drop the deferred
migration in the case !CALLOUT_PENDING in callout_stop_safe()?
Attilio
--
Peace can only be achieved by understanding - A. Einstein
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