| Message ID | 20220901221720.1105021-4-joel@joelfernandes.org (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | 3a27fc0233bebc4486a2a90b8c9f0cb69d443732 |
| Headers | show |
| Series | Implement call_rcu_lazy() and miscellaneous fixes | expand |
On Thu, Sep 01, 2022 at 10:17:05PM +0000, Joel Fernandes (Google) wrote: > The rnp->qsmask is locklessly accessed from rcutree_dying_cpu(). This > may help avoid load/store tearing due to concurrent access, KCSAN Nit: you can avoid only load tearing with READ_ONCE(). Regards, Boqun > issues, and preserve sanity of people reading the mask in tracing. > > Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org> > --- > kernel/rcu/tree.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > index 0ca21ac0f064..5ec97e3f7468 100644 > --- a/kernel/rcu/tree.c > +++ b/kernel/rcu/tree.c > @@ -2106,7 +2106,7 @@ int rcutree_dying_cpu(unsigned int cpu) > if (!IS_ENABLED(CONFIG_HOTPLUG_CPU)) > return 0; > > - blkd = !!(rnp->qsmask & rdp->grpmask); > + blkd = !!(READ_ONCE(rnp->qsmask) & rdp->grpmask); > trace_rcu_grace_period(rcu_state.name, READ_ONCE(rnp->gp_seq), > blkd ? TPS("cpuofl-bgp") : TPS("cpuofl")); > return 0; > -- > 2.37.2.789.g6183377224-goog >
On 9/6/2022 6:26 PM, Boqun Feng wrote: > On Thu, Sep 01, 2022 at 10:17:05PM +0000, Joel Fernandes (Google) wrote: >> The rnp->qsmask is locklessly accessed from rcutree_dying_cpu(). This >> may help avoid load/store tearing due to concurrent access, KCSAN > > Nit: you can avoid only load tearing with READ_ONCE(). > I modified it as you suggested for the next revision, thanks.
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 0ca21ac0f064..5ec97e3f7468 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -2106,7 +2106,7 @@ int rcutree_dying_cpu(unsigned int cpu) if (!IS_ENABLED(CONFIG_HOTPLUG_CPU)) return 0; - blkd = !!(rnp->qsmask & rdp->grpmask); + blkd = !!(READ_ONCE(rnp->qsmask) & rdp->grpmask); trace_rcu_grace_period(rcu_state.name, READ_ONCE(rnp->gp_seq), blkd ? TPS("cpuofl-bgp") : TPS("cpuofl")); return 0;
The rnp->qsmask is locklessly accessed from rcutree_dying_cpu(). This may help avoid load/store tearing due to concurrent access, KCSAN issues, and preserve sanity of people reading the mask in tracing. Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org> --- kernel/rcu/tree.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)