Attachment 153475 Details for Bug 198014 – Proposed patch

[patch] Proposed patch

umtx_pi_disown.patch (text/plain), 2.48 KB, created by eric on 2015-02-24 21:21:30 UTC

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Creator: eric

Created: 2015-02-24 21:21:30 UTC

Size: 2.48 KB

patch

obsolete

>commit b9676e3146be582ab768f37a34119f31b7f93f74
>Author: evangyzen <eric_van_gyzen@dell.com>
>Date:   Sun Feb 22 14:05:47 2015 -0500
>
>    When unlocking a contested PI mutex, disown the umtx_pi even if the umtxq is empty
>    
>    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 <eric_van_gyzen@dell.com>
>                  with advice from: Elliott Rabe and Jim Muchow, also at Dell Inc.
>    Obtained from: Dell Inc.
>
>diff --git a/sys/kern/kern_umtx.c b/sys/kern/kern_umtx.c
>index 317e05b..cc7c16d 100644
>--- a/sys/kern/kern_umtx.c
>+++ b/sys/kern/kern_umtx.c
>@@ -1445,6 +1445,19 @@ umtx_pi_setowner(struct umtx_pi *pi, struct thread *owner)
> 	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 umutex *m, uint32_t flags)
> 			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 +1895,21 @@ do_unlock_pi(struct thread *td, struct umutex *m, uint32_t flags)
> 		mtx_unlock_spin(&umtx_lock);
> 		if (uq_first)
> 			umtxq_signal_thread(uq_first);
>+	} else {
>+		pi = umtx_pi_lookup(&key);
>+		if (pi != NULL) {
>+			/*
>+			 * This can happen 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.
>+			 * This thread might not own the umtx_pi in this case,
>+			 * but if it does, 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);
>

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