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 5c0930ccaa
("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.
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Merge tag 'urgent-rcu.2024.01.24a' of https://github.com/neeraju/linux
Pull RCU fix from Neeraj Upadhyay:
"This 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
5c0930ccaa ("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"
* tag 'urgent-rcu.2024.01.24a' of https://github.com/neeraju/linux:
rcu: Defer RCU kthreads wakeup when CPU is dying
3cb9871f81