Date: Thu, 3 May 2012 14:49:13 +0300 From: Konstantin Belousov <kostikbel@gmail.com> To: Attilio Rao <attilio@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: <20120503114913.GJ2358@deviant.kiev.zoral.com.ua> In-Reply-To: <CAJ-FndBF7%2BfLwivrMdH=rMHsEVQ5jojk3noceN8wxmaj2ZaTvg@mail.gmail.com> References: <201205031038.q43Ac2eZ032779@svn.freebsd.org> <CAJ-FndBF7%2BfLwivrMdH=rMHsEVQ5jojk3noceN8wxmaj2ZaTvg@mail.gmail.com>
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--VSonL41MObbAuehL Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Thu, May 03, 2012 at 12:02:08PM +0100, Attilio Rao wrote: > 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. >=20 > Can you please clarify why you cannot simply drop the deferred > migration in the case !CALLOUT_PENDING in callout_stop_safe()? I probably can, I think I went with the route of committed patch because it is slightly less work. Also, the comment in the while() loop suggested me to rely on softclock. --VSonL41MObbAuehL Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.12 (FreeBSD) iEYEARECAAYFAk+icLkACgkQC3+MBN1Mb4ifBgCguBFmr3XD/vfD28mhzWhtEXC0 3toAoMDSGc/ElSj2X5E+Y1QGocG/Gd1a =NClt -----END PGP SIGNATURE----- --VSonL41MObbAuehL--
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