Revert "rw_semaphore: remove up/down_read_non_owner"
authorKent Overstreet <koverstreet@google.com>
Thu, 22 Sep 2011 04:43:05 +0000 (21:43 -0700)
committerKent Overstreet <koverstreet@google.com>
Sat, 23 Mar 2013 22:53:52 +0000 (15:53 -0700)
commit84759c6d18c5144432781ddca037d929ee9db8a5
treea2f7507dbd760ad87d607c9e80a4c79d96222502
parenta937536b868b8369b98967929045f1df54234323
Revert "rw_semaphore: remove up/down_read_non_owner"

This reverts commit 11b80f459adaf91a712f95e7734a17655a36bf30.

Bcache needs rw semaphores for cache coherency in writeback mode -
writes have to take a read lock on a per cache device rw sem, and
release it when the bio completes.

But since this is for bios it's naturally not in the context of the
process that originally took the lock.

Signed-off-by: Kent Overstreet <koverstreet@google.com>
CC: Christoph Hellwig <hch@infradead.org>
CC: David Howells <dhowells@redhat.com>
include/linux/rwsem.h
kernel/rwsem.c