From: J. Bruce Fields <bfields@redhat.com>
Date: Tue, 4 Jan 2011 19:12:47 +0000 (-0500)
Subject: svcrpc: ensure cache_check caller sees updated entry
X-Git-Tag: v2.6.38-rc1~51^2~31
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=fdef7aa5d4020fd94ffcbf0078d6bd9e5a111e19;p=pandora-kernel.git

svcrpc: ensure cache_check caller sees updated entry

Supposes cache_check runs simultaneously with an update on a different
CPU:

	cache_check			task doing update
	^^^^^^^^^^^			^^^^^^^^^^^^^^^^^

	1. test for CACHE_VALID		1'. set entry->data
	   & !CACHE_NEGATIVE

	2. use entry->data		2'. set CACHE_VALID

If the two memory writes performed in step 1' and 2' appear misordered
with respect to the reads in step 1 and 2, then the caller could get
stale data at step 2 even though it saw CACHE_VALID set on the cache
entry.

Add memory barriers to prevent this.

Reviewed-by: NeilBrown <neilb@suse.de>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
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