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Ankur Arora be6ab68820 rcu: handle quiescent states for PREEMPT_RCU=n, PREEMPT_COUNT=y
[ Upstream commit 83b28cfe796464ebbde1cf7916c126da6d572685 ]

With PREEMPT_RCU=n, cond_resched() provides urgently needed quiescent
states for read-side critical sections via rcu_all_qs().
One reason why this was needed: lacking preempt-count, the tick
handler has no way of knowing whether it is executing in a
read-side critical section or not.

With (PREEMPT_LAZY=y, PREEMPT_DYNAMIC=n), we get (PREEMPT_COUNT=y,
PREEMPT_RCU=n). In this configuration cond_resched() is a stub and
does not provide quiescent states via rcu_all_qs().
(PREEMPT_RCU=y provides this information via rcu_read_unlock() and
its nesting counter.)

So, use the availability of preempt_count() to report quiescent states
in rcu_flavor_sched_clock_irq().

Suggested-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
2025-06-04 14:32:34 +02:00
arch MIPS: pm-cps: Use per-CPU variables as per-CPU, not per-core 2025-06-04 14:32:33 +02:00
block block: fix 'kmem_cache of name 'bio-108' already exists' 2025-04-10 14:29:37 +02:00
certs
crypto crypto: null - Use spin lock instead of mutex 2025-05-02 07:39:27 +02:00
Documentation x86/bugs: Make spectre user default depend on MITIGATION_SPECTRE_V2 2025-06-04 14:32:32 +02:00
drivers vxlan: Annotate FDB data races 2025-06-04 14:32:34 +02:00
fs orangefs: Do not truncate file size 2025-06-04 14:32:32 +02:00
include net/mlx4_core: Avoid impossible mlx4_db_alloc() order value 2025-06-04 14:32:33 +02:00
init sched/isolation: Make CONFIG_CPU_ISOLATION depend on CONFIG_SMP 2025-05-02 07:39:28 +02:00
ipc ipc: replace costly bailout check in sysvipc_find_ipc() 2024-09-04 13:15:02 +02:00
kernel rcu: handle quiescent states for PREEMPT_RCU=n, PREEMPT_COUNT=y 2025-06-04 14:32:34 +02:00
lib dql: Fix dql->limit value when reset. 2025-06-04 14:32:30 +02:00
LICENSES
mm mm: add missing release barrier on PGDAT_RECLAIM_LOCKED unlock 2025-05-02 07:39:16 +02:00
net ip: fib_rules: Fetch net from fib_rule in fib[46]_rule_configure(). 2025-06-04 14:32:34 +02:00
samples samples/bpf: Fix a resource leak 2024-12-14 19:44:50 +01:00
scripts kbuild: fix argument parsing in scripts/config 2025-06-04 14:32:31 +02:00
security smack: recognize ipv4 CIPSO w/o categories 2025-06-04 14:32:33 +02:00
sound ASoC: ops: Enforce platform maximum on initial value 2025-06-04 14:32:33 +02:00
tools tools/build: Don't pass test log files to linker 2025-06-04 14:32:30 +02:00
usr
virt KVM: arm64: Ignore PMCNTENSET_EL0 while checking for overflow status 2024-12-19 18:05:04 +01:00
.clang-format
.cocciconfig
.get_maintainer.ignore
.gitattributes
.gitignore Remove *.orig pattern from .gitignore 2024-11-08 16:20:33 +01:00
.mailmap
COPYING
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Makefile Linux 5.4.293 2025-05-02 07:39:30 +02:00
README

Linux kernel
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There are various text files in the Documentation/ subdirectory,
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Please read the Documentation/process/changes.rst file, as it contains the
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