From: Paul E. McKenney Date: Fri, 8 Apr 2022 16:21:50 +0000 (-0700) Subject: rcu-tasks: Handle sparse cpu_possible_mask in rcu_tasks_invoke_cbs() X-Git-Tag: v5.18.3~803 X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=0a2103507619ef842ed30f0eb9296c0f489b9ed2;p=thirdparty%2Fkernel%2Fstable.git 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 Signed-off-by: Paul E. McKenney Signed-off-by: Sasha Levin --- diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h index b43320b149d24..00ff0896fb000 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));