Attachment 311900 Details for Bug 452974 – rwlock: be more conservative in locking reader_lock_count

rwlock: be more conservative in locking reader_lock_count

conservative_lock_count.patch (text/plain), 5.51 KB, created by IBM Bug Proxy on 2008-07-16 00:30:39 UTC

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Creator: IBM Bug Proxy

Created: 2008-07-16 00:30:39 UTC

Size: 5.51 KB

patch

obsolete

>From rostedt@goodmis.org Mon Jul 14 23:05:15 2008
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>Date: Mon, 14 Jul 2008 22:53:21 -0400 (EDT)
>From: Steven Rostedt <rostedt@goodmis.org>
>X-X-Sender: rostedt@gandalf.stny.rr.com
>To: john stultz <johnstul@us.ibm.com>
>Subject: [PATCH] rwlock: be more conservative in locking reader_lock_count
>Message-ID: <Pine.LNX.4.58.0807142252230.4530@gandalf.stny.rr.com>
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>
>John can you try this patch and see if it fixes the warning you get. It
>may be that the warning is an actual bug.
>
>-- Steve
>
>
>Signed-off-by: Steven Rostedt <srostedt@redhat.com>
>---
> kernel/rtmutex.c |   16 ++++++++--------
> 1 file changed, 8 insertions(+), 8 deletions(-)
>
>Index: linux-2.6.24.7-rt-73/kernel/rtmutex.c
>===================================================================
>--- linux-2.6.24.7-rt-73.orig/kernel/rtmutex.c	2008-07-14 22:27:13.000000000 -0400
>+++ linux-2.6.24.7-rt-73/kernel/rtmutex.c	2008-07-14 22:30:54.000000000 -0400
>@@ -1137,16 +1137,13 @@ rt_rwlock_update_owner(struct rw_mutex *
> 	if (own == RT_RW_READER)
> 		return;
>
>-	/*
>-	 * We don't need to grab the pi_lock to look at the reader list
>-	 * since we hold the rwm wait_lock. We only care about the pointer
>-	 * to this lock, and we own the wait_lock, so that pointer
>-	 * can't be changed.
>-	 */
>+	spin_lock(&own->pi_lock);
> 	for (i = own->reader_lock_count - 1; i >= 0; i--) {
> 		if (own->owned_read_locks[i].lock == rwm)
> 			break;
> 	}
>+	spin_unlock(&own->pi_lock);
>+
> 	/* It is possible the owner didn't add it yet */
> 	if (i < 0)
> 		return;
>@@ -1453,7 +1450,6 @@ __rt_read_fasttrylock(struct rw_mutex *r
> 			current->owned_read_locks[reader_count].count = 1;
> 		} else
> 			WARN_ON_ONCE(1);
>-		spin_unlock(&current->pi_lock);
> 		/*
> 		 * If this task is no longer the sole owner of the lock
> 		 * or someone is blocking, then we need to add the task
>@@ -1463,12 +1459,16 @@ __rt_read_fasttrylock(struct rw_mutex *r
> 			struct rt_mutex *mutex = &rwm->mutex;
> 			struct reader_lock_struct *rls;
>
>+			/* preserve lock order, we only need wait_lock now */
>+			spin_unlock(&current->pi_lock);
>+
> 			spin_lock(&mutex->wait_lock);
> 			rls = &current->owned_read_locks[reader_count];
> 			if (!rls->list.prev || list_empty(&rls->list))
> 				list_add(&rls->list, &rwm->readers);
> 			spin_unlock(&mutex->wait_lock);
>-		}
>+		} else
>+			spin_unlock(&current->pi_lock);
> 		local_irq_restore(flags);
> 		return 1;
> 	}

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Attachments on bug 452974: 311900