We observed livelocks on ARC SMP setup when running hackbench with SLUB. This hardware configuration lacks atomic instructions (LLOCK/SCOND) thus kernel resorts to a central @smp_bitops_lock to protect any R-M-W ops suh as test_and_set_bit() The spinlock itself is implemented using Atomic [EX]change instruction which is always available. The race happened when both cores tried to slab_lock() the same page. c1 c0 ----------- ----------- slab_lock slab_lock slab_unlock Not observing the unlock This in turn happened because slab_unlock() doesn't serialize properly (doesn't use atomic clear) with a concurrent running slab_lock()->test_and_set_bit() Cc: Christoph Lameter <cl@xxxxxxxxx> Cc: Pekka Enberg <penberg@xxxxxxxxxx> Cc: David Rientjes <rientjes@xxxxxxxxxx> Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Cc: Noam Camus <noamc@xxxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Cc: <linux-mm@xxxxxxxxx> Cc: <linux-kernel@xxxxxxxxxxxxxxx> Cc: <linux-snps-arc@xxxxxxxxxxxxxxxxxxx> Signed-off-by: Vineet Gupta <vgupta@xxxxxxxxxxxx> --- mm/slub.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/slub.c b/mm/slub.c index d8fbd4a6ed59..b7d345a508dc 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -345,7 +345,7 @@ static __always_inline void slab_lock(struct page *page) static __always_inline void slab_unlock(struct page *page) { VM_BUG_ON_PAGE(PageTail(page), page); - __bit_spin_unlock(PG_locked, &page->flags); + bit_spin_unlock(PG_locked, &page->flags); } static inline void set_page_slub_counters(struct page *page, unsigned long counters_new) -- 2.5.0 -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html