From: Paul E. McKenney Date: Wed, 11 Dec 2013 21:59:09 +0000 (-0800) Subject: Documentation/memory-barriers.txt: Downgrade UNLOCK+BLOCK X-Git-Tag: v3.14-rc1~175^2~15 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=17eb88e068430014deb709e5af34197cdf2390c9;p=pandora-kernel.git Documentation/memory-barriers.txt: Downgrade UNLOCK+BLOCK Historically, an UNLOCK+LOCK pair executed by one CPU, by one task, or on a given lock variable has implied a full memory barrier. In a recent LKML thread, the wisdom of this historical approach was called into question: http://www.spinics.net/lists/linux-mm/msg65653.html, in part due to the memory-order complexities of low-handoff-overhead queued locks on x86 systems. This patch therefore removes this guarantee from the documentation, and further documents how to restore it via a new smp_mb__after_unlock_lock() primitive. Signed-off-by: Paul E. McKenney Reviewed-by: Peter Zijlstra Cc: Cc: Linus Torvalds Cc: Andrew Morton Link: http://lkml.kernel.org/r/1386799151-2219-6-git-send-email-paulmck@linux.vnet.ibm.com Signed-off-by: Ingo Molnar --- Reading git-diff-tree failed