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rcu: Use _full() API to debug synchronize_rcu()

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Switch for using of get_state_synchronize_rcu_full() and
poll_state_synchronize_rcu_full() pair to debug a normal
synchronize_rcu() call.

Just using "not" full APIs to identify if a grace period is
passed or not might lead to a false-positive kernel splat.

It can happen, because get_state_synchronize_rcu() compresses
both normal and expedited states into one single unsigned long
value, so a poll_state_synchronize_rcu() can miss GP-completion
when synchronize_rcu()/synchronize_rcu_expedited() concurrently
run.

To address this, switch to poll_state_synchronize_rcu_full() and
get_state_synchronize_rcu_full() APIs, which use separate variables
for expedited and normal states.

Reported-by: cheung wall <zzqq0103.hey@gmail.com>
Closes: https://lore.kernel.org/lkml/Z5ikQeVmVdsWQrdD@pc636/T/
Fixes: 988f569ae041 ("rcu: Reduce synchronize_rcu() latency")
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Link: https://lore.kernel.org/r/20250227131613.52683-3-urezki@gmail.com
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
This commit is contained in:
Uladzislau Rezki (Sony) 2025-02-27 14:16:13 +01:00 committed by Boqun Feng
parent a6cea3954e
commit 5a562b8b3f
2 changed files with 6 additions and 5 deletions
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3
include/linux/rcupdate_wait.h
View File

@ -16,6 +16,9 @@
struct rcu_synchronize {
struct rcu_head head;
struct completion completion;
/* This is for debugging. */
struct rcu_gp_oldstate oldstate;
};
void wakeme_after_rcu(struct rcu_head *head);

8
kernel/rcu/tree.c
View File

@ -1612,12 +1612,10 @@ static void rcu_sr_normal_complete(struct llist_node *node)
{
struct rcu_synchronize *rs = container_of(
(struct rcu_head *) node, struct rcu_synchronize, head);
unsigned long oldstate = (unsigned long) rs->head.func;
WARN_ONCE(IS_ENABLED(CONFIG_PROVE_RCU) &&
!poll_state_synchronize_rcu(oldstate),
"A full grace period is not passed yet: %lu",
rcu_seq_diff(get_state_synchronize_rcu(), oldstate));
!poll_state_synchronize_rcu_full(&rs->oldstate),
"A full grace period is not passed yet!\n");
/* Finally. */
complete(&rs->completion);
@ -3218,7 +3216,7 @@ static void synchronize_rcu_normal(void)
* snapshot before adding a request.
*/
if (IS_ENABLED(CONFIG_PROVE_RCU))
rs.head.func = (void *) get_state_synchronize_rcu();
get_state_synchronize_rcu_full(&rs.oldstate);
rcu_sr_normal_add_req(&rs);