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| author | Joel Fernandes (Google) <joel@joelfernandes.org> | 2023-09-05 00:02:11 +0000 |
|---|---|---|
| committer | Frederic Weisbecker <frederic@kernel.org> | 2023-09-11 22:36:40 +0200 |
| commit | b96e7a5fa0ba9cda32888e04f8f4bac42d49a7f8 (patch) | |
| tree | 9ce65a16b4e7f2a93222559b5b2b05b635cb8f0a /kernel/rcu/tree.c | |
| parent | 7c1b3e0c988f2902695ef6175ab8ad00c0e8b65f (diff) | |
| download | linux-b96e7a5fa0ba9cda32888e04f8f4bac42d49a7f8.tar.gz linux-b96e7a5fa0ba9cda32888e04f8f4bac42d49a7f8.tar.bz2 linux-b96e7a5fa0ba9cda32888e04f8f4bac42d49a7f8.zip | |
rcu/tree: Defer setting of jiffies during stall reset
There are instances where rcu_cpu_stall_reset() is called when jiffies
did not get a chance to update for a long time. Before jiffies is
updated, the CPU stall detector can go off triggering false-positives
where a just-started grace period appears to be ages old. In the past,
we disabled stall detection in rcu_cpu_stall_reset() however this got
changed [1]. This is resulting in false-positives in KGDB usecase [2].
Fix this by deferring the update of jiffies to the third run of the FQS
loop. This is more robust, as, even if rcu_cpu_stall_reset() is called
just before jiffies is read, we would end up pushing out the jiffies
read by 3 more FQS loops. Meanwhile the CPU stall detection will be
delayed and we will not get any false positives.
[1] https://lore.kernel.org/all/20210521155624.174524-2-senozhatsky@chromium.org/
[2] https://lore.kernel.org/all/20230814020045.51950-2-chenhuacai@loongson.cn/
Tested with rcutorture.cpu_stall option as well to verify stall behavior
with/without patch.
Tested-by: Huacai Chen <chenhuacai@loongson.cn>
Reported-by: Binbin Zhou <zhoubinbin@loongson.cn>
Closes: https://lore.kernel.org/all/20230814020045.51950-2-chenhuacai@loongson.cn/
Suggested-by: Paul McKenney <paulmck@kernel.org>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Fixes: a80be428fbc1 ("rcu: Do not disable GP stall detection in rcu_cpu_stall_reset()")
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Diffstat (limited to 'kernel/rcu/tree.c')
| -rw-r--r-- | kernel/rcu/tree.c | 12 |
1 files changed, 12 insertions, 0 deletions
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index cb1caefa8bd0..d85779f67aea 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -1556,10 +1556,22 @@ static bool rcu_gp_fqs_check_wake(int *gfp) */ static void rcu_gp_fqs(bool first_time) { + int nr_fqs = READ_ONCE(rcu_state.nr_fqs_jiffies_stall); struct rcu_node *rnp = rcu_get_root(); WRITE_ONCE(rcu_state.gp_activity, jiffies); WRITE_ONCE(rcu_state.n_force_qs, rcu_state.n_force_qs + 1); + + WARN_ON_ONCE(nr_fqs > 3); + /* Only countdown nr_fqs for stall purposes if jiffies moves. */ + if (nr_fqs) { + if (nr_fqs == 1) { + WRITE_ONCE(rcu_state.jiffies_stall, + jiffies + rcu_jiffies_till_stall_check()); + } + WRITE_ONCE(rcu_state.nr_fqs_jiffies_stall, --nr_fqs); + } + if (first_time) { /* Collect dyntick-idle snapshots. */ force_qs_rnp(dyntick_save_progress_counter); |