Author: kib Date: Wed Feb 25 16:12:56 2015 New Revision: 279282 URL: https://svnweb.freebsd.org/changeset/base/279282
Log: When unlocking a contested PI pthread mutex, if the queue of waiters is empty, look up the umtx_pi and disown it if the current thread owns it. This can happen if a signal or timeout removed the last waiter from the queue, but there is still a thread in do_lock_pi() holding a reference on the umtx_pi. The unlocking thread might not own the umtx_pi in this case, but if it does, it must disown it to keep the ownership consistent between the umtx_pi and the umutex. Submitted by: Eric van Gyzen <[email protected]> with advice from: Elliott Rabe and Jim Muchow, also at Dell Inc. Obtained from: Dell Inc. PR: 198914 Modified: head/sys/kern/kern_umtx.c Modified: head/sys/kern/kern_umtx.c ============================================================================== --- head/sys/kern/kern_umtx.c Wed Feb 25 13:58:43 2015 (r279281) +++ head/sys/kern/kern_umtx.c Wed Feb 25 16:12:56 2015 (r279282) @@ -1445,6 +1445,19 @@ umtx_pi_setowner(struct umtx_pi *pi, str TAILQ_INSERT_TAIL(&uq_owner->uq_pi_contested, pi, pi_link); } + +/* + * Disown a PI mutex, and remove it from the owned list. + */ +static void +umtx_pi_disown(struct umtx_pi *pi) +{ + + mtx_assert(&umtx_lock, MA_OWNED); + TAILQ_REMOVE(&pi->pi_owner->td_umtxq->uq_pi_contested, pi, pi_link); + pi->pi_owner = NULL; +} + /* * Claim ownership of a PI mutex. */ @@ -1861,8 +1874,7 @@ do_unlock_pi(struct thread *td, struct u return (EPERM); } uq_me = curthread->td_umtxq; - pi->pi_owner = NULL; - TAILQ_REMOVE(&uq_me->uq_pi_contested, pi, pi_link); + umtx_pi_disown(pi); /* get highest priority thread which is still sleeping. */ uq_first = TAILQ_FIRST(&pi->pi_blocked); while (uq_first != NULL && @@ -1883,6 +1895,25 @@ do_unlock_pi(struct thread *td, struct u mtx_unlock_spin(&umtx_lock); if (uq_first) umtxq_signal_thread(uq_first); + } else { + pi = umtx_pi_lookup(&key); + /* + * A umtx_pi can exist if a signal or timeout removed the + * last waiter from the umtxq, but there is still + * a thread in do_lock_pi() holding the umtx_pi. + */ + if (pi != NULL) { + /* + * The umtx_pi can be unowned, such as when a thread + * has just entered do_lock_pi(), allocated the + * umtx_pi, and unlocked the umtxq. + * If the current thread owns it, it must disown it. + */ + mtx_lock_spin(&umtx_lock); + if (pi->pi_owner == td) + umtx_pi_disown(pi); + mtx_unlock_spin(&umtx_lock); + } } umtxq_unlock(&key); _______________________________________________ [email protected] mailing list http://lists.freebsd.org/mailman/listinfo/svn-src-head To unsubscribe, send any mail to "[email protected]"
