Hi, On Wed, 4 Jun 2014, Tejun Heo wrote: > On Wed, Jun 04, 2014 at 03:58:24PM +0200, Sebastian Ott wrote: > > From 82295633cad58c7d6b9af4e470e3168ed43a6779 Mon Sep 17 00:00:00 2001 > > From: Heiko Carstens <heiko.carst...@de.ibm.com> > > Date: Wed, 4 Jun 2014 12:53:19 +0200 > > Subject: [PATCH] percpu-refcount: fix usage of this_cpu_ops > > > > 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 <k...@daterainc.com> > > Cc: Tejun Heo <t...@kernel.org> > > Cc: <sta...@vger.kernel.org> # v3.11+ > > Reported-by: Sebastian Ott <seb...@linux.vnet.ibm.com> > > Signed-off-by: Heiko Carstens <heiko.carst...@de.ibm.com> > > Bah... should have caught it way back. Sorry about that. Appying to > percpu/for-3.15-fixes with stable cc'd. >
In your git tree you've used me as the patch author but that should be Heiko. Sorry if I didn't annotate this correctly - I just inlined the git format-patch output.. Thanks, Sebastian -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/