Author: kib Date: Thu Jul 28 09:09:55 2016 New Revision: 303426 URL: https://svnweb.freebsd.org/changeset/base/303426
Log: Rewrite subr_sleepqueue.c use of callouts to not depend on the specifics of callout KPI. Esp., do not depend on the exact interface of callout_stop(9) return values. The main change is that instead of requiring precise callouts, code maintains absolute time to wake up. Callouts now should ensure that a wake occurs at the requested moment, but we can tolerate both run-away callout, and callout_stop(9) lying about running callout either way. As consequence, it removes the constant source of the bugs where sleepq_check_timeout() causes uninterruptible thread state where the thread is detached from CPU, see e.g. r234952 and r296320. Patch also removes dual meaning of the TDF_TIMEOUT flag, making code (IMO much) simpler to reason about. Tested by: pho Reviewed by: jhb Sponsored by: The FreeBSD Foundation MFC after: 1 month Differential revision: https://reviews.freebsd.org/D7137 Modified: head/sys/ddb/db_ps.c head/sys/kern/kern_thread.c head/sys/kern/subr_sleepqueue.c head/sys/sys/proc.h Modified: head/sys/ddb/db_ps.c ============================================================================== --- head/sys/ddb/db_ps.c Thu Jul 28 08:57:01 2016 (r303425) +++ head/sys/ddb/db_ps.c Thu Jul 28 09:09:55 2016 (r303426) @@ -375,8 +375,13 @@ DB_SHOW_COMMAND(thread, db_show_thread) db_printf(" lock: %s turnstile: %p\n", td->td_lockname, td->td_blocked); if (TD_ON_SLEEPQ(td)) - db_printf(" wmesg: %s wchan: %p\n", td->td_wmesg, - td->td_wchan); + db_printf( + " wmesg: %s wchan: %p sleeptimo %lx. %jx (curr %lx. %jx)\n", + td->td_wmesg, td->td_wchan, + (long)sbttobt(td->td_sleeptimo).sec, + (uintmax_t)sbttobt(td->td_sleeptimo).frac, + (long)sbttobt(sbinuptime()).sec, + (uintmax_t)sbttobt(sbinuptime()).frac); db_printf(" priority: %d\n", td->td_priority); db_printf(" container lock: %s (%p)\n", lock->lo_name, lock); if (td->td_swvoltick != 0) { Modified: head/sys/kern/kern_thread.c ============================================================================== --- head/sys/kern/kern_thread.c Thu Jul 28 08:57:01 2016 (r303425) +++ head/sys/kern/kern_thread.c Thu Jul 28 09:09:55 2016 (r303426) @@ -318,7 +318,7 @@ thread_reap(void) /* * Don't even bother to lock if none at this instant, - * we really don't care about the next instant.. + * we really don't care about the next instant. */ if (!TAILQ_EMPTY(&zombie_threads)) { mtx_lock_spin(&zombie_lock); @@ -383,6 +383,7 @@ thread_free(struct thread *td) if (td->td_kstack != 0) vm_thread_dispose(td); vm_domain_policy_cleanup(&td->td_vm_dom_policy); + callout_drain(&td->td_slpcallout); uma_zfree(thread_zone, td); } @@ -580,6 +581,7 @@ thread_wait(struct proc *p) td->td_cpuset = NULL; cpu_thread_clean(td); thread_cow_free(td); + callout_drain(&td->td_slpcallout); thread_reap(); /* check for zombie threads etc. */ } Modified: head/sys/kern/subr_sleepqueue.c ============================================================================== --- head/sys/kern/subr_sleepqueue.c Thu Jul 28 08:57:01 2016 (r303425) +++ head/sys/kern/subr_sleepqueue.c Thu Jul 28 09:09:55 2016 (r303426) @@ -378,6 +378,7 @@ sleepq_set_timeout_sbt(void *wchan, sbin { struct sleepqueue_chain *sc; struct thread *td; + sbintime_t pr1; td = curthread; sc = SC_LOOKUP(wchan); @@ -387,8 +388,14 @@ sleepq_set_timeout_sbt(void *wchan, sbin MPASS(wchan != NULL); if (cold) panic("timed sleep before timers are working"); - callout_reset_sbt_on(&td->td_slpcallout, sbt, pr, - sleepq_timeout, td, PCPU_GET(cpuid), flags | C_DIRECT_EXEC); + KASSERT(td->td_sleeptimo == 0, ("td %d %p td_sleeptimo %jx", + td->td_tid, td, (uintmax_t)td->td_sleeptimo)); + thread_lock(td); + callout_when(sbt, pr, flags, &td->td_sleeptimo, &pr1); + thread_unlock(td); + callout_reset_sbt_on(&td->td_slpcallout, td->td_sleeptimo, pr1, + sleepq_timeout, td, PCPU_GET(cpuid), flags | C_PRECALC | + C_DIRECT_EXEC); } /* @@ -576,37 +583,36 @@ static int sleepq_check_timeout(void) { struct thread *td; + int res; td = curthread; THREAD_LOCK_ASSERT(td, MA_OWNED); /* - * If TDF_TIMEOUT is set, we timed out. + * If TDF_TIMEOUT is set, we timed out. But recheck + * td_sleeptimo anyway. */ - if (td->td_flags & TDF_TIMEOUT) { - td->td_flags &= ~TDF_TIMEOUT; - return (EWOULDBLOCK); + res = 0; + if (td->td_sleeptimo != 0) { + if (td->td_sleeptimo <= sbinuptime()) + res = EWOULDBLOCK; + td->td_sleeptimo = 0; } - - /* - * If TDF_TIMOFAIL is set, the timeout ran after we had - * already been woken up. - */ - if (td->td_flags & TDF_TIMOFAIL) - td->td_flags &= ~TDF_TIMOFAIL; - - /* - * If callout_stop() fails, then the timeout is running on - * another CPU, so synchronize with it to avoid having it - * accidentally wake up a subsequent sleep. - */ - else if (_callout_stop_safe(&td->td_slpcallout, CS_EXECUTING, NULL) - == 0) { - td->td_flags |= TDF_TIMEOUT; - TD_SET_SLEEPING(td); - mi_switch(SW_INVOL | SWT_SLEEPQTIMO, NULL); - } - return (0); + if (td->td_flags & TDF_TIMEOUT) + td->td_flags &= ~TDF_TIMEOUT; + else + /* + * We ignore the situation where timeout subsystem was + * unable to stop our callout. The struct thread is + * type-stable, the callout will use the correct + * memory when running. The checks of the + * td_sleeptimo value in this function and in + * sleepq_timeout() ensure that the thread does not + * get spurious wakeups, even if the callout was reset + * or thread reused. + */ + callout_stop(&td->td_slpcallout); + return (res); } /* @@ -914,12 +920,17 @@ sleepq_timeout(void *arg) CTR3(KTR_PROC, "sleepq_timeout: thread %p (pid %ld, %s)", (void *)td, (long)td->td_proc->p_pid, (void *)td->td_name); - /* - * First, see if the thread is asleep and get the wait channel if - * it is. - */ thread_lock(td); - if (TD_IS_SLEEPING(td) && TD_ON_SLEEPQ(td)) { + + if (td->td_sleeptimo > sbinuptime() || td->td_sleeptimo == 0) { + /* + * The thread does not want a timeout (yet). + */ + } else if (TD_IS_SLEEPING(td) && TD_ON_SLEEPQ(td)) { + /* + * See if the thread is asleep and get the wait + * channel if it is. + */ wchan = td->td_wchan; sc = SC_LOOKUP(wchan); THREAD_LOCKPTR_ASSERT(td, &sc->sc_lock); @@ -927,40 +938,16 @@ sleepq_timeout(void *arg) MPASS(sq != NULL); td->td_flags |= TDF_TIMEOUT; wakeup_swapper = sleepq_resume_thread(sq, td, 0); - thread_unlock(td); - if (wakeup_swapper) - kick_proc0(); - return; - } - - /* - * If the thread is on the SLEEPQ but isn't sleeping yet, it - * can either be on another CPU in between sleepq_add() and - * one of the sleepq_*wait*() routines or it can be in - * sleepq_catch_signals(). - */ - if (TD_ON_SLEEPQ(td)) { + } else if (TD_ON_SLEEPQ(td)) { + /* + * If the thread is on the SLEEPQ but isn't sleeping + * yet, it can either be on another CPU in between + * sleepq_add() and one of the sleepq_*wait*() + * routines or it can be in sleepq_catch_signals(). + */ td->td_flags |= TDF_TIMEOUT; - thread_unlock(td); - return; } - /* - * Now check for the edge cases. First, if TDF_TIMEOUT is set, - * then the other thread has already yielded to us, so clear - * the flag and resume it. If TDF_TIMEOUT is not set, then the - * we know that the other thread is not on a sleep queue, but it - * hasn't resumed execution yet. In that case, set TDF_TIMOFAIL - * to let it know that the timeout has already run and doesn't - * need to be canceled. - */ - if (td->td_flags & TDF_TIMEOUT) { - MPASS(TD_IS_SLEEPING(td)); - td->td_flags &= ~TDF_TIMEOUT; - TD_CLR_SLEEPING(td); - wakeup_swapper = setrunnable(td); - } else - td->td_flags |= TDF_TIMOFAIL; thread_unlock(td); if (wakeup_swapper) kick_proc0(); Modified: head/sys/sys/proc.h ============================================================================== --- head/sys/sys/proc.h Thu Jul 28 08:57:01 2016 (r303425) +++ head/sys/sys/proc.h Thu Jul 28 09:09:55 2016 (r303426) @@ -282,6 +282,7 @@ struct thread { int td_no_sleeping; /* (k) Sleeping disabled count. */ int td_dom_rr_idx; /* (k) RR Numa domain selection. */ void *td_su; /* (k) FFS SU private */ + sbintime_t td_sleeptimo; /* (t) Sleep timeout. */ #define td_endzero td_sigmask /* Copied during fork1() or create_thread(). */ @@ -388,7 +389,7 @@ do { \ #define TDF_ALLPROCSUSP 0x00000200 /* suspended by SINGLE_ALLPROC */ #define TDF_BOUNDARY 0x00000400 /* Thread suspended at user boundary */ #define TDF_ASTPENDING 0x00000800 /* Thread has some asynchronous events. */ -#define TDF_TIMOFAIL 0x00001000 /* Timeout from sleep after we were awake. */ +#define TDF_UNUSED12 0x00001000 /* --available-- */ #define TDF_SBDRY 0x00002000 /* Stop only on usermode boundary. */ #define TDF_UPIBLOCKED 0x00004000 /* Thread blocked on user PI mutex. */ #define TDF_NEEDSUSPCHK 0x00008000 /* Thread may need to suspend. */ _______________________________________________ [email protected] mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-all To unsubscribe, send any mail to "[email protected]"
