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authorMark Rutland <mark.rutland@arm.com>2015-03-25 15:55:23 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2015-03-25 16:20:30 -0700
commit859b7a0e89120505c304d7afbbe90325abaa0a6b (patch)
tree78e3c160a7169e3b7dbf8ef9100f618b6c9692b5 /mm
parentmm/memory hotplug: postpone the reset of obsolete pgdat (diff)
downloadlinux-dev-859b7a0e89120505c304d7afbbe90325abaa0a6b.tar.xz
linux-dev-859b7a0e89120505c304d7afbbe90325abaa0a6b.zip
mm/slub: fix lockups on PREEMPT && !SMP kernels
Commit 9aabf810a67c ("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: ldr x4, [x0,#8] loop: ldr x1, [x0,#8] cmp x1, x4 b.ne loop 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 <mark.rutland@arm.com> Cc: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Christoph Lameter <cl@linux.com> Cc: David Rientjes <rientjes@google.com> Cc: Jesper Dangaard Brouer <brouer@redhat.com> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com> Cc: Pekka Enberg <penberg@kernel.org> Cc: Steve Capper <steve.capper@linaro.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm')
-rw-r--r--mm/slub.c6
1 files changed, 4 insertions, 2 deletions
diff --git a/mm/slub.c b/mm/slub.c
index 6832c4eab104..82c473780c91 100644
--- a/mm/slub.c
+++ b/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();