diff options
| author | Neeraj Upadhyay <quic_neeraju@quicinc.com> | 2022-06-09 12:43:40 +0530 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@kernel.org> | 2022-07-19 11:40:00 -0700 |
| commit | a03ae49c4785c1bc7b940e38bbdf2e63d79d1470 (patch) | |
| tree | 707f5236b259cbc0cbfd169f77b015a712e16b36 /kernel/rcu | |
| parent | 9bdb5b3a8d8ad1c92db309219859fe1c87c95351 (diff) | |
rcu/tree: Add comment to describe GP-done condition in fqs loop
Add a comment to explain why !rcu_preempt_blocked_readers_cgp() condition
is required on root rnp node, for GP completion check in rcu_gp_fqs_loop().
Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Neeraj Upadhyay <quic_neeraju@quicinc.com>
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 a23877a773be..7c2231823e84 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -2005,7 +2005,15 @@ static noinline_for_stack void rcu_gp_fqs_loop(void) rcu_gp_torture_wait(); WRITE_ONCE(rcu_state.gp_state, RCU_GP_DOING_FQS); /* Locking provides needed memory barriers. */ - /* If grace period done, leave loop. */ + /* + * Exit the loop if the root rcu_node structure indicates that the grace period + * has ended, leave the loop. The rcu_preempt_blocked_readers_cgp(rnp) check + * is required only for single-node rcu_node trees because readers blocking + * the current grace period are queued only on leaf rcu_node structures. + * For multi-node trees, checking the root node's ->qsmask suffices, because a + * given root node's ->qsmask bit is cleared only when all CPUs and tasks from + * the corresponding leaf nodes have passed through their quiescent state. + */ if (!READ_ONCE(rnp->qsmask) && !rcu_preempt_blocked_readers_cgp(rnp)) break; |