FAILED: patch "[PATCH] entry: Explicitly flush pending rcuog wakeup before last" failed to apply to 4.4-stable tree

PATCH [email protected] 1 participant 1 message Mar 1, 2021

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Stable branch RCU Generic entry code

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2021-03-01 11:31 UTC #0 lore raw

The patch below does not apply to the 4.4-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 47b8ff194c1fd73d58dc339b597d466fe48c8958 Mon Sep 17 00:00:00 2001
From: Frederic Weisbecker <[email protected]>
Date: Mon, 1 Feb 2021 00:05:47 +0100
Subject: [PATCH] entry: Explicitly flush pending rcuog wakeup before last
rescheduling point

Following the idle loop model, cleanly check for pending rcuog wakeup before the last rescheduling point on resuming to user mode. This way we can avoid to do it from rcu_user_enter() with the last resort self-IPI hack that enforces rescheduling.

Signed-off-by Frederic Weisbecker <[email protected]>

Signed-off-by Peter Zijlstra (Intel) <[email protected]>

Signed-off-by Ingo Molnar <[email protected]>

Cc [email protected]

Link https://lkml.kernel.org/r/[email protected] open here

kernel/entry/common.c +7 -0

index f09cae37ddd5..8442e5c9cfa2 100644
@@ -184,6 +184,10 @@ static unsigned long exit_to_user_mode_loop(struct pt_regs *regs,
 		 * enabled above.
 		 */
 		local_irq_disable_exit_to_user();
+
+		/* Check if any of the above work has queued a deferred wakeup */
+		rcu_nocb_flush_deferred_wakeup();
+
 		ti_work = READ_ONCE(current_thread_info()->flags);
 	}

@@ -197,6 +201,9 @@ static void exit_to_user_mode_prepare(struct pt_regs *regs)
 
 	lockdep_assert_irqs_disabled();
 
+	/* Flush pending rcuog wakeup before the last need_resched() check */
+	rcu_nocb_flush_deferred_wakeup();
+
 	if (unlikely(ti_work & EXIT_TO_USER_MODE_WORK))
 		ti_work = exit_to_user_mode_loop(regs, ti_work);

kernel/rcu/tree.c +7 -5

index 4b1e5bd16492..2ebc211fffcb 100644
@@ -707,13 +707,15 @@ noinstr void rcu_user_enter(void)
 	lockdep_assert_irqs_disabled();
 
 	/*
-	 * We may be past the last rescheduling opportunity in the entry code.
-	 * Trigger a self IPI that will fire and reschedule once we resume to
-	 * user/guest mode.
+	 * Other than generic entry implementation, we may be past the last
+	 * rescheduling opportunity in the entry code. Trigger a self IPI
+	 * that will fire and reschedule once we resume in user/guest mode.
 	 */
 	instrumentation_begin();
-	if (do_nocb_deferred_wakeup(rdp) && need_resched())
-		irq_work_queue(this_cpu_ptr(&late_wakeup_work));
+	if (!IS_ENABLED(CONFIG_GENERIC_ENTRY) || (current->flags & PF_VCPU)) {
+		if (do_nocb_deferred_wakeup(rdp) && need_resched())
+			irq_work_queue(this_cpu_ptr(&late_wakeup_work));
+	}
 	instrumentation_end();
 
 	rcu_eqs_enter(true);