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    Subject[PATCH 5.17 070/772] rcu-tasks: Handle sparse cpu_possible_mask in rcu_tasks_invoke_cbs()
    Date
    From: Paul E. McKenney <paulmck@kernel.org>

    [ 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@google.com>
    Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    kernel/rcu/tasks.h | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    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));
    --
    2.35.1


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