On Wed, Aug 15, 2012 at 03:11:41PM +0100, Ben Hutchings wrote: > On Wed, 2012-08-15 at 07:08 -0700, Greg Kroah-Hartman wrote: > > On Wed, Aug 15, 2012 at 02:56:22PM +0100, Ben Hutchings wrote: > > > On Mon, 2012-08-13 at 13:18 -0700, Greg Kroah-Hartman wrote: > > > > From: Greg KH <gre...@linuxfoundation.org> > > > > > > > > 3.5-stable review patch. If anyone has any objections, please let me > > > > know. > > > > > > > > ------------------ > > > > > > > > From: Will Deacon <will.dea...@arm.com> > > > > > > > > commit a76d7bd96d65fa5119adba97e1b58d95f2e78829 upstream. > > > > > > > > The open-coded mutex implementation for ARMv6+ cores suffers from a > > > > severe lack of barriers, so in the uncontended case we don't actually > > > > protect any accesses performed during the critical section. > > > > > > > > Furthermore, the code is largely a duplication of the ARMv6+ atomic_dec > > > > code but optimised to remove a branch instruction, as the mutex fastpath > > > > was previously inlined. Now that this is executed out-of-line, we can > > > > reuse the atomic access code for the locking (in fact, we use the xchg > > > > code as this produces shorter critical sections). > > > > > > > > This patch uses the generic xchg based implementation for mutexes on > > > > ARMv6+, which introduces barriers to the lock/unlock operations and also > > > > has the benefit of removing a fair amount of inline assembly code. > > > [...] > > > > > > Here also, I think this should be deferred. > > > > "also"? Am I missing some context here? Why should we deferr this one? > > What do we need to wait for? > > This is the same as 3.4.9-rc1 patch 10/65, which I queried as it > apparently caused a regression. > > Will Deacon wrote: > > The additional patch should also be CC'd to stable and is sitting in -tip > > somewhere I believe, so it shouldn't be long before it does hit mainline. > > > > Without this patch there's a memory-ordering bug (which we seem to have hit > > once in > 5 years). With the patch there's a mutex lockup issue on SMP > > systems > > that I can provoke with enough hackbenching, so you may want to hold off for > > now.
Ah, ok, missed that. How about I just drop this for now, and when someone (Will?) feels it is "good enough time to wait", they will resend it to sta...@vger.kernel.org so that we can add it then? Otherwise I'll just loose it somewhere. Now dropped. greg k-h -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
