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. Ben. -- Ben Hutchings I say we take off; nuke the site from orbit. It's the only way to be sure.
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