Date: Thu, 3 May 2012 12:02:08 +0100 From: Attilio Rao <attilio@freebsd.org> To: Konstantin Belousov <kib@freebsd.org> Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org Subject: Re: svn commit: r234952 - in head/sys: kern sys Message-ID: <CAJ-FndBF7%2BfLwivrMdH=rMHsEVQ5jojk3noceN8wxmaj2ZaTvg@mail.gmail.com> In-Reply-To: <201205031038.q43Ac2eZ032779@svn.freebsd.org> References: <201205031038.q43Ac2eZ032779@svn.freebsd.org>
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2012/5/3, Konstantin Belousov <kib@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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