tree 25e3bccce50977e9199df4ee0445a3af9e5da708
parent 1370e97bb2eb1ef2df7355204e5a4ba13e12b861
author Waiman Long <Waiman.Long@hp.com> 1378997735 -0400
committer Linus Torvalds <torvalds@linux-foundation.org> 1379003123 -0700

dcache: get/release read lock in read_seqbegin_or_lock() & friend

This patch modifies read_seqbegin_or_lock() and need_seqretry() to use
newly introduced read_seqlock_excl() and read_sequnlock_excl()
primitives so that they won't change the sequence number even if they
fall back to take the lock.  This is OK as no change to the protected
data structure is being made.

It will prevent one fallback to lock taking from cascading into a series
of lock taking reducing performance because of the sequence number
change.  It will also allow other sequence readers to go forward while
an exclusive reader lock is taken.

This patch also updates some of the inaccurate comments in the code.

Signed-off-by: Waiman Long <Waiman.Long@hp.com>
To: Alexander Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>