This is a note to let you know that I've just added the patch titled
rcu-tasks: Handle sparse cpu_possible_mask in rcu_tasks_invoke_cbs()
to the 5.17-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
rcu-tasks-handle-sparse-cpu_possible_mask-in-rcu_tas.patch
and it can be found in the queue-5.17 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 835986639dfdf1dac4085bd9c675fb5ef26a50ab
Author: Paul E. McKenney <paulmck@xxxxxxxxxx>
Date: Fri Apr 8 09:21:50 2022 -0700
rcu-tasks: Handle sparse cpu_possible_mask in rcu_tasks_invoke_cbs()
[ Upstream commit ab2756ea6b74987849b44ad0e33c3cfec159033b ]
If the cpu_possible_mask is sparse (for example, if bits are set only for
CPUs 0, 4, 8, ...), then rcu_tasks_invoke_cbs() will access per-CPU data
for a CPU not in cpu_possible_mask. It makes these accesses while doing
a workqueue-based binary search for non-empty callback lists. Although
this search must pass through CPUs not represented in cpu_possible_mask,
it has no need to check the callback list for such CPUs.
This commit therefore changes the rcu_tasks_invoke_cbs() function's
binary search so as to only check callback lists for CPUs present in
cpu_possible_mask.
Reported-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index 30c42797f53b..1664e472524b 100644
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -460,7 +460,7 @@ static void rcu_tasks_invoke_cbs(struct rcu_tasks *rtp, struct rcu_tasks_percpu
}
}
- if (rcu_segcblist_empty(&rtpcp->cblist))
+ if (rcu_segcblist_empty(&rtpcp->cblist) || !cpu_possible(cpu))
return;
raw_spin_lock_irqsave_rcu_node(rtpcp, flags);
rcu_segcblist_advance(&rtpcp->cblist, rcu_seq_current(&rtp->tasks_gp_seq));
