https://github.com/torvalds/linux
Revision 0c36b390a546055b6815d4b93a2c9fed4d980ffb authored by Sebastian Ott on 04 June 2014, 13:58:24 UTC, committed by Tejun Heo on 04 June 2014, 16:12:29 UTC
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@daterainc.com> Cc: <stable@vger.kernel.org> # v3.11+ Reported-by: Sebastian Ott <sebott@linux.vnet.ibm.com> Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com> Signed-off-by: Tejun Heo <tj@kernel.org> References: http://lkml.kernel.org/g/alpine.LFD.2.11.1406041540520.21183@denkbrett
1 parent 5a838c3
Tip revision: 0c36b390a546055b6815d4b93a2c9fed4d980ffb authored by Sebastian Ott on 04 June 2014, 13:58:24 UTC
percpu-refcount: fix usage of this_cpu_ops
percpu-refcount: fix usage of this_cpu_ops
Tip revision: 0c36b39
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