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| author |   Paul E. McKenney <paulmck@kernel.org> | 2022-02-16 09:54:56 -0800 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@kernel.org> | 2022-04-11 17:28:48 -0700 |
| commit | 90d2efe7bdbde5371b6122174af0718843f805c6 (patch) | |
| tree | 5cc5da7957665dffb8028c2daf41a3a377908c98 /kernel/rcu/tree_plugin.h | |
| parent | rcu: Clarify fill-the-gap comment in rcu_segcblist_advance() (diff) | |
| download | linux-dev-90d2efe7bdbde5371b6122174af0718843f805c6.tar.xz linux-dev-90d2efe7bdbde5371b6122174af0718843f805c6.zip | |
rcu: Fix rcu_preempt_deferred_qs_irqrestore() strict QS reporting
Suppose we have a kernel built with both CONFIG_RCU_STRICT_GRACE_PERIOD=y
and CONFIG_PREEMPT=y. Suppose further that an RCU reader from which RCU
core needs a quiescent state ends in rcu_preempt_deferred_qs_irqrestore().
This function will then invoke rcu_report_qs_rdp() in order to immediately
report that quiescent state. Unfortunately, it will not have cleared
that reader's CPU's rcu_data structure's ->cpu_no_qs.b.norm field.
As a result, rcu_report_qs_rdp() will take an early exit because it
will believe that this CPU has not yet encountered a quiescent state,
and there will be no reporting of the current quiescent state.
This commit therefore causes rcu_preempt_deferred_qs_irqrestore() to
clear the ->cpu_no_qs.b.norm field before invoking rcu_report_qs_rdp().
Kudos to Boqun Feng and Neeraj Upadhyay for helping with analysis of
this issue!
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Diffstat (limited to 'kernel/rcu/tree_plugin.h')
| -rw-r--r-- | kernel/rcu/tree_plugin.h | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index 8360d86db1c0..176639c6215f 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -486,6 +486,7 @@ rcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags) t->rcu_read_unlock_special.s = 0; if (special.b.need_qs) { if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD)) { + rdp->cpu_no_qs.b.norm = false; rcu_report_qs_rdp(rdp); udelay(rcu_unlock_delay); } else { |