Patch "tick: Move got_idle_tick away from common flags" has been added to the 6.6-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

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

    tick: Move got_idle_tick away from common flags

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:
     tick-move-got_idle_tick-away-from-common-flags.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 f842d78ffd0ec0941e4113afec3e3e0bcb60035c
Author: Frederic Weisbecker <frederic@xxxxxxxxxx>
Date:   Sun Feb 25 23:55:03 2024 +0100

    tick: Move got_idle_tick away from common flags
    
    [ Upstream commit 3ce74f1a8566dbbc9774f85fb0ce781fe290fd32 ]
    
    tick_nohz_idle_got_tick() is called by cpuidle_reflect() within the idle
    loop with interrupts enabled. This function modifies the struct
    tick_sched's bitfield "got_idle_tick". However this bitfield is stored
    within the same mask as other bitfields that can be modified from
    interrupts.
    
    Fortunately so far it looks like the only race that can happen is while
    writing ->got_idle_tick to 0, an interrupt fires and writes the
    ->idle_active field to 0. It's then possible that the interrupted write
    to ->got_idle_tick writes back the old value of ->idle_active back to 1.
    
    However if that happens, the worst possible outcome is that the time
    spent between that interrupt and the upcoming call to
    tick_nohz_idle_exit() is accounted as idle, which is negligible quantity.
    
    Still all the bitfield writes within this struct tick_sched's shadow
    mask should be IRQ-safe. Therefore move this bitfield out to its own
    storage to avoid further suprises.
    
    Signed-off-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
    Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
    Reviewed-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
    Link: https://lore.kernel.org/r/20240225225508.11587-12-frederic@xxxxxxxxxx
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/kernel/time/tick-sched.h b/kernel/time/tick-sched.h
index 5ed5a9d41d5a7..03a586e12cf89 100644
--- a/kernel/time/tick-sched.h
+++ b/kernel/time/tick-sched.h
@@ -61,7 +61,6 @@ struct tick_sched {
 	unsigned int			tick_stopped	: 1;
 	unsigned int			idle_active	: 1;
 	unsigned int			do_timer_last	: 1;
-	unsigned int			got_idle_tick	: 1;
 
 	/* Tick handling: jiffies stall check */
 	unsigned int			stalled_jiffies;
@@ -73,6 +72,7 @@ struct tick_sched {
 	ktime_t				next_tick;
 	unsigned long			idle_jiffies;
 	ktime_t				idle_waketime;
+	unsigned int			got_idle_tick;
 
 	/* Idle entry */
 	seqcount_t			idle_sleeptime_seq;