From 30106b8ce2cc2243514116d6f29086e6deecc754 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Wed, 4 May 2011 15:38:19 +0200 Subject: [PATCH] slub: Fix the lockless code on 32-bit platforms with no 64-bit cmpxchg The SLUB allocator use of the cmpxchg_double logic was wrong: it actually needs the irq-safe one. That happens automatically when we use the native unlocked 'cmpxchg8b' instruction, but when compiling the kernel for older x86 CPUs that do not support that instruction, we fall back to the generic emulation code. And if you don't specify that you want the irq-safe version, the generic code ends up just open-coding the cmpxchg8b equivalent without any protection against interrupts or preemption. Which definitely doesn't work for SLUB. This was reported by Werner Landgraf , who saw instability with his distro-kernel that was compiled to support pretty much everything under the sun. Most big Linux distributions tend to compile for PPro and later, and would never have noticed this problem. This also fixes the prototypes for the irqsafe cmpxchg_double functions to use 'bool' like they should. [ Btw, that whole "generic code defaults to no protection" design just sounds stupid - if the code needs no protection, there is no reason to use "cmpxchg_double" to begin with. So we should probably just remove the unprotected version entirely as pointless. - Linus ] Signed-off-by: Thomas Gleixner Reported-and-tested-by: werner Acked-and-tested-by: Ingo Molnar Acked-by: Christoph Lameter Cc: Pekka Enberg Cc: Jens Axboe Cc: Tejun Heo Link: http://lkml.kernel.org/r/alpine.LFD.2.02.1105041539050.3005@ionos Signed-off-by: Ingo Molnar Signed-off-by: Linus Torvalds --- include/linux/percpu.h | 2 +- mm/slub.c | 4 ++-- 2 files changed, 3 insertions(+), 3 deletions(-) diff --git a/include/linux/percpu.h b/include/linux/percpu.h index 3a5c4449fd36..8b97308e65df 100644 --- a/include/linux/percpu.h +++ b/include/linux/percpu.h @@ -948,7 +948,7 @@ do { \ irqsafe_generic_cpu_cmpxchg_double(pcp1, pcp2, oval1, oval2, nval1, nval2) # endif # define irqsafe_cpu_cmpxchg_double(pcp1, pcp2, oval1, oval2, nval1, nval2) \ - __pcpu_double_call_return_int(irqsafe_cpu_cmpxchg_double_, (pcp1), (pcp2), (oval1), (oval2), (nval1), (nval2)) + __pcpu_double_call_return_bool(irqsafe_cpu_cmpxchg_double_, (pcp1), (pcp2), (oval1), (oval2), (nval1), (nval2)) #endif #endif /* __LINUX_PERCPU_H */ diff --git a/mm/slub.c b/mm/slub.c index 94d2a33a866e..9d2e5e46bf09 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -1940,7 +1940,7 @@ redo: * Since this is without lock semantics the protection is only against * code executing on this cpu *not* from access by other cpus. */ - if (unlikely(!this_cpu_cmpxchg_double( + if (unlikely(!irqsafe_cpu_cmpxchg_double( s->cpu_slab->freelist, s->cpu_slab->tid, object, tid, get_freepointer(s, object), next_tid(tid)))) { @@ -2145,7 +2145,7 @@ redo: set_freepointer(s, object, c->freelist); #ifdef CONFIG_CMPXCHG_LOCAL - if (unlikely(!this_cpu_cmpxchg_double( + if (unlikely(!irqsafe_cpu_cmpxchg_double( s->cpu_slab->freelist, s->cpu_slab->tid, c->freelist, tid, object, next_tid(tid)))) { -- 2.34.1