Patch "entry: Explicitly flush pending rcuog wakeup before last rescheduling point" has been added to the 5.10-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

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

    entry: Explicitly flush pending rcuog wakeup before last rescheduling point

to the 5.10-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:
     entry-explicitly-flush-pending-rcuog-wakeup-before-l.patch
and it can be found in the queue-5.10 subdirectory.

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



commit 20ed96c067f883754be413dacb263dd5b3938fe5
Author: Frederic Weisbecker <frederic@xxxxxxxxxx>
Date:   Mon Feb 1 00:05:47 2021 +0100

    entry: Explicitly flush pending rcuog wakeup before last rescheduling point
    
    [ Upstream commit 47b8ff194c1fd73d58dc339b597d466fe48c8958 ]
    
    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 <frederic@xxxxxxxxxx>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
    Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
    Cc: stable@xxxxxxxxxxxxxxx
    Link: https://lkml.kernel.org/r/20210131230548.32970-5-frederic@xxxxxxxxxx
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/kernel/entry/common.c b/kernel/entry/common.c
index e289e6773292..d6587e10bd4c 100644
--- a/kernel/entry/common.c
+++ b/kernel/entry/common.c
@@ -174,6 +174,10 @@ 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);
 	}
 
@@ -187,6 +191,9 @@ 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);
 
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index f137a599941b..0d8a2e2df221 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -699,13 +699,15 @@ 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);