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| author | Joel Fernandes <joelagnelf@nvidia.com> | 2025-07-15 16:01:53 -0400 |
|---|---|---|
| committer | Neeraj Upadhyay <neeraj.iitr10@gmail.com> | 2025-07-22 17:09:35 +0530 |
| commit | 30a7806adab5f6b971cf07439ed6a3fac3fd80cf (patch) | |
| tree | 979c6b33a947fc86469cab48b22c93ccca2bdb0e /kernel/rcu/tree.c | |
| parent | 908a97eba8c8b510996bf5d77d1e3070d59caa6d (diff) | |
rcu: Document GP init vs hotplug-scan ordering requirements
Add detailed comments explaining the critical ordering constraints
during RCU grace period initialization, based on discussions with
Frederic.
Reviewed-by: "Paul E. McKenney" <paulmck@kernel.org>
Co-developed-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
Signed-off-by: Neeraj Upadhyay (AMD) <neeraj.upadhyay@kernel.org>
Diffstat (limited to 'kernel/rcu/tree.c')
| -rw-r--r-- | kernel/rcu/tree.c | 8 |
1 files changed, 8 insertions, 0 deletions
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 8c22db759978..384af6b5cf9c 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -1838,6 +1838,14 @@ static noinline_for_stack bool rcu_gp_init(void) start_new_poll = rcu_sr_normal_gp_init(); /* Record GP times before starting GP, hence rcu_seq_start(). */ old_gp_seq = rcu_state.gp_seq; + /* + * Critical ordering: rcu_seq_start() must happen BEFORE the CPU hotplug + * scan below. Otherwise we risk a race where a newly onlining CPU could + * be missed by the current grace period, potentially leading to + * use-after-free errors. For a detailed explanation of this race, see + * Documentation/RCU/Design/Requirements/Requirements.rst in the + * "Hotplug CPU" section. + */ rcu_seq_start(&rcu_state.gp_seq); /* Ensure that rcu_seq_done_exact() guardband doesn't give false positives. */ WARN_ON_ONCE(IS_ENABLED(CONFIG_PROVE_RCU) && |