From: Michel Lespinasse <walken@google.com>
Date: Tue, 7 May 2013 13:46:00 +0000 (-0700)
Subject: rwsem: do not block readers at head of queue if other readers are active
X-Git-Tag: omap-for-v3.10/dt-fixes-for-merge-window~14^2~2
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=25c39325968bbcebe6cd2a1991228c9dfb48d655;p=pandora-kernel.git

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>
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