linux-kernel - [PATCH 0/3] timer_migration: Fix a possible race and improvements

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Message-Id: <20240621-tmigr-fixes-v1-0-8c8a2d8e8d77@linutronix.de>
Date: Fri, 21 Jun 2024 11:37:05 +0200
From: Anna-Maria Behnsen <anna-maria@...utronix.de>
To: Frederic Weisbecker <frederic@...nel.org>, 
 Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org
Cc: Borislav Petkov <bp@...en8.de>, 
 Anna-Maria Behnsen <anna-maria@...utronix.de>, 
 Narasimhan V <Narasimhan.V@....com>
Subject: [PATCH 0/3] timer_migration: Fix a possible race and improvements

Borislav reported a warning in timer migration deactive path

  https://lore.kernel.org/r/20240612090347.GBZmlkc5PwlVpOG6vT@fat_crate.local

Sadly it doesn't reproduce directly. But with the change of timing (by
adding a trace prinkt before the warning), it is possible to trigger the
warning reliable at least in my test setup. The problem here is a racy
check agains group->parent pointer. This is also used in other places in
the code and fixing this racy usage is adressed by the first patch.

While working with the code, I saw two things which could be improved
(tracing and update of per cpu group wakeup value). This improvements are
adressed by the other two patches.

Patches are available here:

  https://git.kernel.org/pub/scm/linux/kernel/git/anna-maria/linux-devel.git timers/misc

Cc: Frederic Weisbecker <frederic@...nel.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: linux-kernel@...r.kernel.org

Thanks,

Anna-Maria

---
Anna-Maria Behnsen (3):
      timer_migration: Do not rely always on group->parent
      timer_migration: Spare write when nothing changed
      timer_migration: Improve tracing

 kernel/time/timer_migration.c | 55 ++++++++++++++++++++-----------------------
 kernel/time/timer_migration.h | 12 +++++++++-
 2 files changed, 36 insertions(+), 31 deletions(-)