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| author | Paul E. McKenney | 2022-11-25 08:43:10 -0800 |
|---|---|---|
| committer | Paul E. McKenney | 2023-01-03 17:28:34 -0800 |
| commit | 95ff24ee7b809ff8d253cd5edf196f137ae08c44 (patch) | |
| tree | ecbfd21506fa48ad1a35a1ffac9b6eff8a5f928f /kernel/rcu | |
| parent | 253cbbff621407a6265ce7a6a03c3766f8846f02 (diff) | |
rcu: Upgrade header comment for poll_state_synchronize_rcu()
This commit emphasizes the possibility of concurrent calls to
synchronize_rcu() and synchronize_rcu_expedited() causing one or
the other of the two grace periods being lost from the viewpoint of
poll_state_synchronize_rcu().
If you cannot afford to lose grace periods this way, you should
instead use the _full() variants of the polled RCU API, for
example, poll_state_synchronize_rcu_full().
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Diffstat (limited to 'kernel/rcu')
| -rw-r--r-- | kernel/rcu/tree.c | 10 |
1 files changed, 9 insertions, 1 deletions
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 7d3a59d4f37e..0147e69ea85a 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -3559,7 +3559,9 @@ EXPORT_SYMBOL_GPL(start_poll_synchronize_rcu_full); * If @false is returned, it is the caller's responsibility to invoke this * function later on until it does return @true. Alternatively, the caller * can explicitly wait for a grace period, for example, by passing @oldstate - * to cond_synchronize_rcu() or by directly invoking synchronize_rcu(). + * to either cond_synchronize_rcu() or cond_synchronize_rcu_expedited() + * on the one hand or by directly invoking either synchronize_rcu() or + * synchronize_rcu_expedited() on the other. * * Yes, this function does not take counter wrap into account. * But counter wrap is harmless. If the counter wraps, we have waited for @@ -3570,6 +3572,12 @@ EXPORT_SYMBOL_GPL(start_poll_synchronize_rcu_full); * completed. Alternatively, they can use get_completed_synchronize_rcu() * to get a guaranteed-completed grace-period state. * + * In addition, because oldstate compresses the grace-period state for + * both normal and expedited grace periods into a single unsigned long, + * it can miss a grace period when synchronize_rcu() runs concurrently + * with synchronize_rcu_expedited(). If this is unacceptable, please + * instead use the _full() variant of these polling APIs. + * * This function provides the same memory-ordering guarantees that * would be provided by a synchronize_rcu() that was invoked at the call * to the function that provided @oldstate, and that returned at the end |