linux-kernel - [GIT PULL] RCU regression fix for v6.8

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Date: Thu, 25 Jan 2024 04:13:19 +0530
From: "Neeraj Upadhyay (AMD)" <neeraj.iitr10@...il.com>
To: torvalds@...ux-foundation.org
Cc: linux-kernel@...r.kernel.org, kernel-team@...a.com, paulmck@...nel.org,
	mingo@...nel.org, tglx@...utronix.de, rcu@...r.kernel.org,
	frederic@...nel.org, boqun.feng@...il.com, joel@...lfernandes.org,
	neeraj.upadhyay@....com, urezki@...il.com,
	qiang.zhang1211@...il.com
Subject: [GIT PULL] RCU regression fix for v6.8

Hi Linus,

The following changes since commit 6613476e225e090cc9aad49be7fa504e290dd33d:

  Linux 6.8-rc1 (2024-01-21 14:11:32 -0800)

are available in the Git repository at:

  https://github.com/neeraju/linux.git tags/urgent-rcu.2024.01.24a

for you to fetch changes up to e787644caf7628ad3269c1fbd321c3255cf51710:

  rcu: Defer RCU kthreads wakeup when CPU is dying (2024-01-24 22:46:17 +0530)

----------------------------------------------------------------
Urgent RCU pull request for v6.8

This commit fixes RCU grace period stalls, which are observed when
an outgoing CPU's quiescent state reporting results in wakeup of
one of the grace period kthreads, to complete the grace period. If
those kthreads have SCHED_FIFO policy, the wake up can indirectly
arm the RT bandwith timer to the local offline CPU. Earlier migration
of the hrtimers from the CPU introduced in commit 5c0930ccaad5
("hrtimers: Push pending hrtimers away from outgoing CPU earlier")
results in this timer getting ignored. If the RCU grace period
kthreads are waiting for RT bandwidth to be available, they may
never be actually scheduled, resulting in RCU stall warnings.

----------------------------------------------------------------
Frederic Weisbecker (1):
      rcu: Defer RCU kthreads wakeup when CPU is dying

 kernel/rcu/tree.c     | 34 +++++++++++++++++++++++++++++++++-
 kernel/rcu/tree_exp.h |  3 +--
 2 files changed, 34 insertions(+), 3 deletions(-)