diff options
| author | Joel Fernandes <joelagnelf@nvidia.com> | 2025-02-13 11:47:27 -0500 |
|---|---|---|
| committer | Joel Fernandes <joelagnelf@nvidia.com> | 2025-04-08 14:55:55 -0400 |
| commit | f50ad4b73e1bdf7fb40566650fa11bcb438ad5ce (patch) | |
| tree | 14d890279de338b5f1bfdaf6da7c29da8a1036f9 | |
| parent | 4d949edbc4026eeb81a8f931586cfd4f1de5957e (diff) | |
srcu: Use rcu_seq_done_exact() for polling API
poll_state_synchronize_srcu() uses rcu_seq_done() unlike
poll_state_synchronize_rcu() which uses rcu_seq_done_exact().
The rcu_seq_done_exact() makes more sense for polling API, as with
this API, there is a higher chance that there is a significant delay
between the get_state..() and poll_state..() calls since a cookie
can be stored and reused at a later time. During such a delay, if
the gp_seq counter progresses more than ULONG_MAX/2 distance, then
poll_state..() may return false for a long time unwantedly.
Fix by using the more accurate rcu_seq_done_exact() API which is
exactly what straight RCU's polling does.
It may make sense, as future work, to add debug code here as well, where
we compare a physical timestamp between get_state..() and poll_state()
calls and yell if significant time has past but the grace period has
still not progressed.
Reviewed-by: Neeraj Upadhyay <Neeraj.Upadhyay@amd.com>
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Kent Overstreet <kent.overstreet@linux.dev>
Cc: Kent Overstreet <kent.overstreet@linux.dev>
Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
| -rw-r--r-- | kernel/rcu/srcutree.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c index 9a59b071501b..48047260697e 100644 --- a/kernel/rcu/srcutree.c +++ b/kernel/rcu/srcutree.c @@ -1589,7 +1589,7 @@ EXPORT_SYMBOL_GPL(start_poll_synchronize_srcu); bool poll_state_synchronize_srcu(struct srcu_struct *ssp, unsigned long cookie) { if (cookie != SRCU_GET_STATE_COMPLETED && - !rcu_seq_done(&ssp->srcu_sup->srcu_gp_seq, cookie)) + !rcu_seq_done_exact(&ssp->srcu_sup->srcu_gp_seq, cookie)) return false; // Ensure that the end of the SRCU grace period happens before // any subsequent code that the caller might execute. |