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| author | Paul E. McKenney <paulmck@kernel.org> | 2025-12-29 22:16:15 +0300 |
|---|---|---|
| committer | Boqun Feng <boqun.feng@gmail.com> | 2026-01-07 16:58:26 +0300 |
| commit | 255019537cfd63d6adc16a55bcbfd79530d5937e (patch) | |
| tree | c6b2db76a5c312d4af67cea20d94c40b29fc20d5 | |
| parent | 8f0b4cce4481fb22653697cced8d0d04027cb1e8 (diff) | |
| download | linux-255019537cfd63d6adc16a55bcbfd79530d5937e.tar.xz | |
rcu: Make expedited RCU CPU stall warnings detect stall-end races
If an expedited RCU CPU stall ends just at the stall-warning timeout,
the current code will print an expedited stall-warning message, but one
that doesn't identify any CPUs or tasks causing the stall. This is most
likely to happen for short-timeout stalls, for example, the 20-millisecond
timeouts that are sometimes used for small embedded devices. Needless to
say, these semi-empty stall-warning messages can be rather confusing.
One option would be to suppress the stall-warning message entirely in
this case, but the near-miss information can be quite valuable.
Detect this race condition and emits a "INFO: Expedited stall ended
before state dump start" message to clarify matters.
[boqun: Apply feedback from Borislav]
Reported-by: Borislav Petkov <bp@alien8.de>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Acked-by: Borislav Petkov (AMD) <bp@alien8.de>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
| -rw-r--r-- | kernel/rcu/tree_exp.h | 7 |
1 files changed, 6 insertions, 1 deletions
diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h index 96c49c56fc14..82cada459e5d 100644 --- a/kernel/rcu/tree_exp.h +++ b/kernel/rcu/tree_exp.h @@ -589,7 +589,12 @@ static void synchronize_rcu_expedited_stall(unsigned long jiffies_start, unsigne pr_cont(" } %lu jiffies s: %lu root: %#lx/%c\n", j - jiffies_start, rcu_state.expedited_sequence, data_race(rnp_root->expmask), ".T"[!!data_race(rnp_root->exp_tasks)]); - if (ndetected) { + if (!ndetected) { + // This is invoked from the grace-period worker, so + // a new grace period cannot have started. And if this + // worker were stalled, we would not get here. ;-) + pr_err("INFO: Expedited stall ended before state dump start\n"); + } else { pr_err("blocking rcu_node structures (internal RCU debug):"); rcu_for_each_node_breadth_first(rnp) { if (rnp == rnp_root) |