On Wed, Oct 09, 2019 at 10:20:17AM +0800, Boqun Feng wrote: [snip] > > Boqun, are you going to be posting another patch which just uses mask_ofl_ipi > > in the for_each(..) loop? (without using _snap) as Paul suggested? > > > > IIUC, Paul already has this fix along with other ->expmask queued in his > dev branch: > > https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git/commit/?h=dev&id=4e4fefe0630dcf7415d62e6d9171c8f209444376 > > , and with the proper "Reported-by" tag to give syzbot credit. Yes, I see it now. So Marco you should be good ;) thanks! - Joel > > Regards, > Boqun > > > Paul mentioned other places where rnp->expmask is locklessly accessed so I > > think that may be fixed separately (such as the stall-warning code). Paul, > > were you planning on fixing all such accesses together (other than this code) > > or should I look into it more? I guess for the stall case, KCSAN would have > > to trigger stalls to see those issues. > > > > thanks, > > > > - Joel > > > > > > > > Thanks! > > > -- Marco > > > > > > > > kernel/rcu/tree_exp.h | 13 ++++++------- > > > > > 1 file changed, 6 insertions(+), 7 deletions(-) > > > > > > > > > > diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h > > > > > index 69c5aa64fcfd..212470018752 100644 > > > > > --- a/kernel/rcu/tree_exp.h > > > > > +++ b/kernel/rcu/tree_exp.h > > > > > @@ -387,10 +387,10 @@ static void sync_rcu_exp_select_node_cpus(struct work_struct *wp) > > > > > } > > > > > ret = smp_call_function_single(cpu, rcu_exp_handler, NULL, 0); > > > > > put_cpu(); > > > > > - if (!ret) { > > > > > - mask_ofl_ipi &= ~mask; > > > > > + /* The CPU responses the IPI, and will report QS itself */ > > > > > + if (!ret) > > > > > continue; > > > > > - } > > > > > + > > > > > /* Failed, raced with CPU hotplug operation. */ > > > > > raw_spin_lock_irqsave_rcu_node(rnp, flags); > > > > > if ((rnp->qsmaskinitnext & mask) && > > > > > @@ -401,13 +401,12 @@ static void sync_rcu_exp_select_node_cpus(struct work_struct *wp) > > > > > schedule_timeout_uninterruptible(1); > > > > > goto retry_ipi; > > > > > } > > > > > - /* CPU really is offline, so we can ignore it. */ > > > > > - if (!(rnp->expmask & mask)) > > > > > - mask_ofl_ipi &= ~mask; > > > > > + /* CPU really is offline, and we need its QS to pass GP. */ > > > > > + if (rnp->expmask & mask) > > > > > + mask_ofl_test |= mask; > > > > > raw_spin_unlock_irqrestore_rcu_node(rnp, flags); > > > > > } > > > > > /* Report quiescent states for those that went offline. */ > > > > > - mask_ofl_test |= mask_ofl_ipi; > > > > > if (mask_ofl_test) > > > > > rcu_report_exp_cpu_mult(rnp, mask_ofl_test, false); > > > > > } > > > > > -- > > > > > 2.23.0 > > > > >
