On Mon, Dec 09, 2013 at 05:28:02PM -0800, Paul E. McKenney wrote: > From: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx> > > The Linux kernel has traditionally required that an UNLOCK+LOCK pair > act as a full memory barrier when either (1) that UNLOCK+LOCK pair > was executed by the same CPU or task, or (2) the same lock variable > was used for the UNLOCK and LOCK. It now seems likely that very few > places in the kernel rely on this full-memory-barrier semantic, and > with the advent of queued locks, providing this semantic either requires > complex reasoning, or for some architectures, added overhead. > > This commit therefore adds a smp_mb__after_unlock_lock(), which may be > placed after a LOCK primitive to restore the full-memory-barrier semantic. > All definitions are currently no-ops, but will be upgraded for some > architectures when queued locks arrive. > > Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> > Cc: Linux-Arch <linux-arch@xxxxxxxxxxxxxxx> > Cc: Ingo Molnar <mingo@xxxxxxxxxx> > Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> > Cc: Oleg Nesterov <oleg@xxxxxxxxxx> > Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> It seems quite unfortunate that this isn't in some common location, and then only overridden by architectures that need to do so. More importantly: you document this earlier in the patch series than you introduce it. - Josh Triplett -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
