diff options
| author | Paul E. McKenney <paulmck@kernel.org> | 2022-04-13 15:17:25 -0700 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@kernel.org> | 2022-06-20 09:21:51 -0700 |
| commit | 414c12385d4741e35d88670c6cc2f40a77809734 (patch) | |
| tree | 4daedd9ad1e492c302496192ce0295856cfe9ee8 /kernel/rcu/tree.c | |
| parent | 2403e8044f222e7c816fb2416661f5f469662973 (diff) | |
rcu: Provide a get_completed_synchronize_rcu() function
It is currently up to the caller to handle stale return values from
get_state_synchronize_rcu(). If poll_state_synchronize_rcu() returned
true once, a grace period has elapsed, regardless of the fact that counter
wrap might cause some future poll_state_synchronize_rcu() invocation to
return false. For example, the caller might store a separate flag that
indicates whether some previous call to poll_state_synchronize_rcu()
determined that the relevant grace period had already ended.
This approach works, but it requires extra storage and is easy to get
wrong. This commit therefore introduces a get_completed_synchronize_rcu()
that returns a cookie that causes poll_state_synchronize_rcu() to always
return true. This already-completed cookie can be stored in place of the
cookie that previously caused poll_state_synchronize_rcu() to return true.
It can also be used to flag a given structure as not having been exposed
to readers, and thus not requiring a grace period to elapse.
This commit is in preparation for polled expedited grace periods.
Link: https://lore.kernel.org/all/20220121142454.1994916-1-bfoster@redhat.com/
Link: https://docs.google.com/document/d/1RNKWW9jQyfjxw2E8dsXVTdvZYh0HnYeSHDKog9jhdN8/edit?usp=sharing
Cc: Brian Foster <bfoster@redhat.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Ian Kent <raven@themaw.net>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Diffstat (limited to 'kernel/rcu/tree.c')
| -rw-r--r-- | kernel/rcu/tree.c | 3 |
1 files changed, 2 insertions, 1 deletions
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index ec28e259774e..46cfceea8784 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -3924,7 +3924,8 @@ EXPORT_SYMBOL_GPL(start_poll_synchronize_rcu); */ bool poll_state_synchronize_rcu(unsigned long oldstate) { - if (rcu_seq_done_exact(&rcu_state.gp_seq, oldstate)) { + if (oldstate == RCU_GET_STATE_COMPLETED || + rcu_seq_done_exact(&rcu_state.gp_seq, oldstate)) { smp_mb(); /* Ensure GP ends before subsequent accesses. */ return true; } |