From 25c39325968bbcebe6cd2a1991228c9dfb48d655 Mon Sep 17 00:00:00 2001
From: Michel Lespinasse <walken@google.com>
Date: Tue, 7 May 2013 06:46:00 -0700
Subject: [PATCH] rwsem: do not block readers at head of queue if other readers
 are active

This change fixes a race condition where a reader might determine it
needs to block, but by the time it acquires the wait_lock the rwsem has
active readers and no queued waiters.

In this situation the reader can run in parallel with the existing
active readers; it does not need to block until the active readers
complete.

Thanks to Peter Hurley for noticing this possible race.

Signed-off-by: Michel Lespinasse <walken@google.com>
Reviewed-by: Peter Hurley <peter@hurleysoftware.com>
Acked-by: Davidlohr Bueso <davidlohr.bueso@hp.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
Reading git-format-patch failed