From: Sebastian Ott <sebott@xxxxxxxxxxxxxxxxxx> 3.12-stable review patch. If anyone has any objections, please let me know. =============== commit 0c36b390a546055b6815d4b93a2c9fed4d980ffb upstream. The percpu-refcount infrastructure uses the underscore variants of this_cpu_ops in order to modify percpu reference counters. (e.g. __this_cpu_inc()). However the underscore variants do not atomically update the percpu variable, instead they may be implemented using read-modify-write semantics (more than one instruction). Therefore it is only safe to use the underscore variant if the context is always the same (process, softirq, or hardirq). Otherwise it is possible to lose updates. This problem is something that Sebastian has seen within the aio subsystem which uses percpu refcounters both in process and softirq context leading to reference counts that never dropped to zeroes; even though the number of "get" and "put" calls matched. Fix this by using the non-underscore this_cpu_ops variant which provides correct per cpu atomic semantics and fixes the corrupted reference counts. Cc: Kent Overstreet <kmo@xxxxxxxxxxxxx> Reported-by: Sebastian Ott <sebott@xxxxxxxxxxxxxxxxxx> Signed-off-by: Heiko Carstens <heiko.carstens@xxxxxxxxxx> Signed-off-by: Tejun Heo <tj@xxxxxxxxxx> References: http://lkml.kernel.org/g/alpine.LFD.2.11.1406041540520.21183@denkbrett Signed-off-by: Jiri Slaby <jslaby@xxxxxxx> --- include/linux/percpu-refcount.h | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/include/linux/percpu-refcount.h b/include/linux/percpu-refcount.h index 95961f0bf62d..0afb48fd449d 100644 --- a/include/linux/percpu-refcount.h +++ b/include/linux/percpu-refcount.h @@ -110,7 +110,7 @@ static inline void percpu_ref_get(struct percpu_ref *ref) pcpu_count = ACCESS_ONCE(ref->pcpu_count); if (likely(REF_STATUS(pcpu_count) == PCPU_REF_PTR)) - __this_cpu_inc(*pcpu_count); + this_cpu_inc(*pcpu_count); else atomic_inc(&ref->count); @@ -139,7 +139,7 @@ static inline bool percpu_ref_tryget(struct percpu_ref *ref) pcpu_count = ACCESS_ONCE(ref->pcpu_count); if (likely(REF_STATUS(pcpu_count) == PCPU_REF_PTR)) { - __this_cpu_inc(*pcpu_count); + this_cpu_inc(*pcpu_count); ret = true; } @@ -164,7 +164,7 @@ static inline void percpu_ref_put(struct percpu_ref *ref) pcpu_count = ACCESS_ONCE(ref->pcpu_count); if (likely(REF_STATUS(pcpu_count) == PCPU_REF_PTR)) - __this_cpu_dec(*pcpu_count); + this_cpu_dec(*pcpu_count); else if (unlikely(atomic_dec_and_test(&ref->count))) ref->release(ref); -- 2.0.0 -- 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