From mboxrd@z Thu Jan 1 00:00:00 1970 From: akpm@linux-foundation.org Subject: [merged] mm-slub-fix-lockups-on-preempt-smp-kernels.patch removed from -mm tree Date: Fri, 27 Mar 2015 11:16:52 -0700 Message-ID: <55159e94.3mkQAS5o7vxjrmrx%akpm@linux-foundation.org> Reply-To: linux-kernel@vger.kernel.org Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Return-path: Received: from mail.linuxfoundation.org ([140.211.169.12]:47702 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753257AbbC0SQx (ORCPT ); Fri, 27 Mar 2015 14:16:53 -0400 Sender: mm-commits-owner@vger.kernel.org List-Id: mm-commits@vger.kernel.org To: mark.rutland@arm.com, brouer@redhat.com, catalin.marinas@arm.com, cl@linux.com, iamjoonsoo.kim@lge.com, penberg@kernel.org, rientjes@google.com, steve.capper@linaro.org, torvalds@linux-foundation.org, mm-commits@vger.kernel.org The patch titled Subject: mm/slub: fix lockups on PREEMPT && !SMP kernels has been removed from the -mm tree. Its filename was mm-slub-fix-lockups-on-preempt-smp-kernels.patch This patch was dropped because it was merged into mainline or a subsystem tree ------------------------------------------------------ From: Mark Rutland Subject: mm/slub: fix lockups on PREEMPT && !SMP kernels Commit 9aabf810a67cd97e ("mm/slub: optimize alloc/free fastpath by removing preemption on/off") introduced an occasional hang for kernels built with CONFIG_PREEMPT && !CONFIG_SMP. The problem is the following loop the patch introduced to slab_alloc_node and slab_free: do { tid = this_cpu_read(s->cpu_slab->tid); c = raw_cpu_ptr(s->cpu_slab); } while (IS_ENABLED(CONFIG_PREEMPT) && unlikely(tid != c->tid)); GCC 4.9 has been observed to hoist the load of c and c->tid above the loop for !SMP kernels (as in this case raw_cpu_ptr(x) is compile-time constant and does not force a reload). On arm64 the generated assembly looks like: ffffffc00016d3c4: f9400404 ldr x4, [x0,#8] ffffffc00016d3c8: f9400401 ldr x1, [x0,#8] ffffffc00016d3cc: eb04003f cmp x1, x4 ffffffc00016d3d0: 54ffffc1 b.ne ffffffc00016d3c8 If the thread is preempted between the load of c->tid (into x1) and tid (into x4), and an allocation or free occurs in another thread (bumping the cpu_slab's tid), the thread will be stuck in the loop until s->cpu_slab->tid wraps, which may be forever in the absence of allocations/frees on the same CPU. This patch changes the loop condition to access c->tid with READ_ONCE. This ensures that the value is reloaded even when the compiler would otherwise assume it could cache the value, and also ensures that the load will not be torn. Signed-off-by: Mark Rutland Cc: Catalin Marinas Acked-by: Christoph Lameter Cc: David Rientjes Cc: Jesper Dangaard Brouer Cc: Joonsoo Kim Cc: Linus Torvalds Cc: Pekka Enberg Cc: Steve Capper Signed-off-by: Andrew Morton --- mm/slub.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff -puN mm/slub.c~mm-slub-fix-lockups-on-preempt-smp-kernels mm/slub.c --- a/mm/slub.c~mm-slub-fix-lockups-on-preempt-smp-kernels +++ a/mm/slub.c @@ -2449,7 +2449,8 @@ redo: do { tid = this_cpu_read(s->cpu_slab->tid); c = raw_cpu_ptr(s->cpu_slab); - } while (IS_ENABLED(CONFIG_PREEMPT) && unlikely(tid != c->tid)); + } while (IS_ENABLED(CONFIG_PREEMPT) && + unlikely(tid != READ_ONCE(c->tid))); /* * Irqless object alloc/free algorithm used here depends on sequence @@ -2718,7 +2719,8 @@ redo: do { tid = this_cpu_read(s->cpu_slab->tid); c = raw_cpu_ptr(s->cpu_slab); - } while (IS_ENABLED(CONFIG_PREEMPT) && unlikely(tid != c->tid)); + } while (IS_ENABLED(CONFIG_PREEMPT) && + unlikely(tid != READ_ONCE(c->tid))); /* Same with comment on barrier() in slab_alloc_node() */ barrier(); _ Patches currently in -mm which might be from mark.rutland@arm.com are origin.patch mm-move-memtest-under-mm.patch memtest-use-phys_addr_t-for-physical-addresses.patch arm64-add-support-for-memtest.patch arm-add-support-for-memtest.patch kconfig-memtest-update-number-of-test-patterns-up-to-17.patch documentation-update-arch-list-in-the-memtest-entry.patch rtc-mediatek-add-mt63xx-rtc-driver.patch linux-next.patch