Patch "srcu: Only accelerate on enqueue time" has been added to the 6.6-stable tree

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This is a note to let you know that I've just added the patch titled

    srcu: Only accelerate on enqueue time

to the 6.6-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:
     srcu-only-accelerate-on-enqueue-time.patch
and it can be found in the queue-6.6 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 96dc51b934d36d275e37584704737a5ef11378c3
Author: Frederic Weisbecker <frederic@xxxxxxxxxx>
Date:   Wed Oct 4 01:29:00 2023 +0200

    srcu: Only accelerate on enqueue time
    
    [ Upstream commit 8a77f38bcd28d3c22ab7dd8eff3f299d43c00411 ]
    
    Acceleration in SRCU happens on enqueue time for each new callback. This
    operation is expected not to fail and therefore any similar attempt
    from other places shouldn't find any remaining callbacks to accelerate.
    
    Moreover accelerations performed beyond enqueue time are error prone
    because rcu_seq_snap() then may return the snapshot for a new grace
    period that is not going to be started.
    
    Remove these dangerous and needless accelerations and introduce instead
    assertions reporting leaking unaccelerated callbacks beyond enqueue
    time.
    
    Co-developed-by: Yong He <alexyonghe@xxxxxxxxxxx>
    Signed-off-by: Yong He <alexyonghe@xxxxxxxxxxx>
    Co-developed-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
    Signed-off-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
    Co-developed-by: Neeraj upadhyay <Neeraj.Upadhyay@xxxxxxx>
    Signed-off-by: Neeraj upadhyay <Neeraj.Upadhyay@xxxxxxx>
    Reviewed-by: Like Xu <likexu@xxxxxxxxxxx>
    Signed-off-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index 7522517b63b6f..2f770a9a2a13a 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -782,8 +782,7 @@ static void srcu_gp_start(struct srcu_struct *ssp)
 	spin_lock_rcu_node(sdp);  /* Interrupts already disabled. */
 	rcu_segcblist_advance(&sdp->srcu_cblist,
 			      rcu_seq_current(&ssp->srcu_sup->srcu_gp_seq));
-	(void)rcu_segcblist_accelerate(&sdp->srcu_cblist,
-				       rcu_seq_snap(&ssp->srcu_sup->srcu_gp_seq));
+	WARN_ON_ONCE(!rcu_segcblist_segempty(&sdp->srcu_cblist, RCU_NEXT_TAIL));
 	spin_unlock_rcu_node(sdp);  /* Interrupts remain disabled. */
 	WRITE_ONCE(ssp->srcu_sup->srcu_gp_start, jiffies);
 	WRITE_ONCE(ssp->srcu_sup->srcu_n_exp_nodelay, 0);
@@ -1719,6 +1718,7 @@ static void srcu_invoke_callbacks(struct work_struct *work)
 	ssp = sdp->ssp;
 	rcu_cblist_init(&ready_cbs);
 	spin_lock_irq_rcu_node(sdp);
+	WARN_ON_ONCE(!rcu_segcblist_segempty(&sdp->srcu_cblist, RCU_NEXT_TAIL));
 	rcu_segcblist_advance(&sdp->srcu_cblist,
 			      rcu_seq_current(&ssp->srcu_sup->srcu_gp_seq));
 	if (sdp->srcu_cblist_invoking ||
@@ -1748,8 +1748,6 @@ static void srcu_invoke_callbacks(struct work_struct *work)
 	 */
 	spin_lock_irq_rcu_node(sdp);
 	rcu_segcblist_add_len(&sdp->srcu_cblist, -len);
-	(void)rcu_segcblist_accelerate(&sdp->srcu_cblist,
-				       rcu_seq_snap(&ssp->srcu_sup->srcu_gp_seq));
 	sdp->srcu_cblist_invoking = false;
 	more = rcu_segcblist_ready_cbs(&sdp->srcu_cblist);
 	spin_unlock_irq_rcu_node(sdp);



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