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author | Frederic Weisbecker <frederic@kernel.org> | 2023-09-08 23:36:03 +0300 |
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committer | Frederic Weisbecker <frederic@kernel.org> | 2023-10-04 23:38:35 +0300 |
commit | a28ab03b499601c14b8f502d875c2bee23209659 (patch) | |
tree | d294fbfd3b574808d54348d25ba9f2d49779fd3d | |
parent | 448e9f34d91d1a4799fdb06a93c2c24b34b6fd9d (diff) | |
download | linux-a28ab03b499601c14b8f502d875c2bee23209659.tar.xz |
rcu: Comment why callbacks migration can't wait for CPUHP_RCUTREE_PREP
The callbacks migration is performed through an explicit call from
the hotplug control CPU right after the death of the target CPU and
before proceeding with the CPUHP_ teardown functions.
This is unusual but necessary and yet uncommented. Summarize the reason
as explained in the changelog of:
a58163d8ca2c (rcu: Migrate callbacks earlier in the CPU-offline timeline)
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
-rw-r--r-- | kernel/cpu.c | 7 |
1 files changed, 7 insertions, 0 deletions
diff --git a/kernel/cpu.c b/kernel/cpu.c index 2491766e1fd5..3b9d5c7eb4a2 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -1372,7 +1372,14 @@ static int takedown_cpu(unsigned int cpu) cpuhp_bp_sync_dead(cpu); tick_cleanup_dead_cpu(cpu); + + /* + * Callbacks must be re-integrated right away to the RCU state machine. + * Otherwise an RCU callback could block a further teardown function + * waiting for its completion. + */ rcutree_migrate_callbacks(cpu); + return 0; } |