Date: Thu, 3 May 2012 10:40:12 GMT From: dfilter@FreeBSD.ORG (dfilter service) To: freebsd-bugs@FreeBSD.org Subject: Re: kern/166340: commit references a PR Message-ID: <201205031040.q43AeCLJ065238@freefall.freebsd.org>
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The following reply was made to PR kern/166340; it has been noted by GNATS. From: dfilter@FreeBSD.ORG (dfilter service) To: bug-followup@FreeBSD.org Cc: Subject: Re: kern/166340: commit references a PR Date: Thu, 3 May 2012 10:38:14 +0000 (UTC) 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. PR: misc/166340 Reported, debugging traces provided and tested by: Christian Esken <christian.esken trivago com> Reviewed by: avg, jhb MFC after: 1 week Modified: head/sys/kern/kern_timeout.c head/sys/sys/callout.h Modified: head/sys/kern/kern_timeout.c ============================================================================== --- head/sys/kern/kern_timeout.c Thu May 3 10:26:33 2012 (r234951) +++ head/sys/kern/kern_timeout.c Thu May 3 10:38:02 2012 (r234952) @@ -645,6 +645,32 @@ softclock(void *arg) cc_cme_cleanup(cc); /* + * Handle deferred callout stops + */ + if ((c->c_flags & CALLOUT_DFRMIGRATION) + == 0) { + CTR3(KTR_CALLOUT, + "deferred cancelled %p func %p arg %p", + c, new_func, new_arg); + if (cc->cc_next == c) { + cc->cc_next = + TAILQ_NEXT(c, + c_links.tqe); + } + if (c->c_flags & + CALLOUT_LOCAL_ALLOC) { + c->c_func = NULL; + SLIST_INSERT_HEAD( + &cc->cc_callfree, c, + c_links.sle); + } + goto nextc; + } else { + c->c_flags &= ~ + CALLOUT_DFRMIGRATION; + } + + /* * It should be assert here that the * callout is not destroyed but that * is not easy. @@ -659,6 +685,9 @@ softclock(void *arg) panic("migration should not happen"); #endif } +#ifdef SMP +nextc: +#endif steps = 0; c = cc->cc_next; } @@ -814,6 +843,7 @@ callout_reset_on(struct callout *c, int cc->cc_migration_ticks = to_ticks; cc->cc_migration_func = ftn; cc->cc_migration_arg = arg; + c->c_flags |= CALLOUT_DFRMIGRATION; CTR5(KTR_CALLOUT, "migration of %p func %p arg %p in %d to %u deferred", c, c->c_func, c->c_arg, to_ticks, cpu); @@ -984,6 +1014,12 @@ again: CC_UNLOCK(cc); KASSERT(!sq_locked, ("sleepqueue chain locked")); return (1); + } else if ((c->c_flags & CALLOUT_DFRMIGRATION) != 0) { + c->c_flags &= ~CALLOUT_DFRMIGRATION; + CTR3(KTR_CALLOUT, "postponing stop %p func %p arg %p", + c, c->c_func, c->c_arg); + CC_UNLOCK(cc); + return (1); } CTR3(KTR_CALLOUT, "failed to stop %p func %p arg %p", c, c->c_func, c->c_arg); Modified: head/sys/sys/callout.h ============================================================================== --- head/sys/sys/callout.h Thu May 3 10:26:33 2012 (r234951) +++ head/sys/sys/callout.h Thu May 3 10:38:02 2012 (r234952) @@ -46,6 +46,7 @@ #define CALLOUT_MPSAFE 0x0008 /* callout handler is mp safe */ #define CALLOUT_RETURNUNLOCKED 0x0010 /* handler returns with mtx unlocked */ #define CALLOUT_SHAREDLOCK 0x0020 /* callout lock held in shared mode */ +#define CALLOUT_DFRMIGRATION 0x0040 /* callout in deferred migration mode */ struct callout_handle { struct callout *callout; _______________________________________________ svn-src-all@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/svn-src-all To unsubscribe, send any mail to "svn-src-all-unsubscribe@freebsd.org"
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