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 <[email protected]> > 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 <[email protected]> > Cc: Tejun Heo <[email protected]> > Cc: <[email protected]> # v3.11+ > Reported-by: Sebastian Ott <[email protected]> > Signed-off-by: Heiko Carstens <[email protected]>
Bah... should have caught it way back. Sorry about that. Appying to percpu/for-3.15-fixes with stable cc'd. Thanks. -- tejun -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
