linux/kernel/rcu, branch master

Merge tag 'rcu.2026.03.31a' of git://git.kernel.org/pub/scm/linux/kernel/git/rcu/linux

2026-04-13T16:36:45Z

Pull RCU updates from Joel Fernandes: "NOCB CPU management: - Consolidate rcu_nocb_cpu_offload() and rcu_nocb_cpu_deoffload() to reduce code duplication - Extract nocb_bypass_needs_flush() helper to reduce duplication in NOCB bypass path rcutorture/torture infrastructure: - Add NOCB01 config for RCU_LAZY torture testing - Add NOCB02 config for NOCB poll mode testing - Add TRIVIAL-PREEMPT config for textbook-style preemptible RCU torture - Test call_srcu() with preemption both disabled and enabled - Remove kvm-check-branches.sh in favor of kvm-series.sh - Make hangs more visible in torture.sh output - Add informative message for tests without a recheck file - Fix numeric test comparison in srcu_lockdep.sh - Use torture_shutdown_init() in refscale and rcuscale instead of open-coded shutdown functions - Fix modulo-zero error in torture_hrtimeout_ns(). SRCU: - Fix SRCU read flavor macro comments - Fix s/they disables/they disable/ typo in srcu_read_unlock_fast() RCU Tasks: - Document that RCU Tasks Trace grace periods now imply RCU grace periods - Remove unnecessary smp_store_release() in cblist_init_generic()" * tag 'rcu.2026.03.31a' of git://git.kernel.org/pub/scm/linux/kernel/git/rcu/linux: rcutorture: Test call_srcu() with preemption disabled and not rcu: Add BOOTPARAM_RCU_STALL_PANIC Kconfig option torture: Avoid modulo-zero error in torture_hrtimeout_ns() rcu/nocb: Extract nocb_bypass_needs_flush() to reduce duplication rcu/nocb: Consolidate rcu_nocb_cpu_offload/deoffload functions rcu-tasks: Remove unnecessary smp_store_release() in cblist_init_generic() rcutorture: Add NOCB02 config for nocb poll mode testing rcutorture: Add NOCB01 config for RCU_LAZY torture testing rcu-tasks: Document that RCU Tasks Trace grace periods now imply RCU grace periods srcu: Fix s/they disables/they disable/ typo in srcu_read_unlock_fast() srcu: Fix SRCU read flavor macro comments rcuscale: Ditch rcu_scale_shutdown in favor of torture_shutdown_init() refscale: Ditch ref_scale_shutdown in favor of torture_shutdown_init() rcutorture: Fix numeric "test" comparison in srcu_lockdep.sh torture: Print informative message for test without recheck file torture: Make hangs more visible in torture.sh output kvm-check-branches.sh: Remove in favor of kvm-series.sh rcutorture: Add a textbook-style trivial preemptible RCU

rcutorture: Test call_srcu() with preemption disabled and not

2026-03-30T19:48:14Z

This commit tests invoking call_srcu() with preemption both enabled and disabled, via acquiring of pi lock. [ Joel: reword commit message. ] Signed-off-by: Paul E. McKenney Signed-off-by: Joel Fernandes

rcu: Add BOOTPARAM_RCU_STALL_PANIC Kconfig option

2026-03-30T19:48:14Z

Add a Kconfig option to set the default value of the kernel.panic_on_rcu_stall sysctl, allowing the kernel to be built with panic-on-RCU-stall enabled by default. This is useful for high-availability systems that require automatic recovery (via panic_timeout) when a CPU stall is detected, without needing userspace to configure the sysctl at boot. This follows the pattern established by BOOTPARAM_SOFTLOCKUP_PANIC and BOOTPARAM_HUNG_TASK_PANIC. The runtime sysctl can still override the Kconfig default. Reviewed-by: Paul E. McKenney Signed-off-by: Gustavo Luiz Duarte Signed-off-by: Joel Fernandes

rcu/nocb: Extract nocb_bypass_needs_flush() to reduce duplication

2026-03-30T19:48:14Z

The bypass flush decision logic is duplicated in rcu_nocb_try_bypass() and nocb_gp_wait() with similar conditions. This commit therefore extracts the functionality into a common helper function nocb_bypass_needs_flush() improving the code readability. A flush_faster parameter is added to controlling the flushing thresholds and timeouts. This design was in the original commit d1b222c6be1f ("rcu/nocb: Add bypass callback queueing") to avoid having the GP kthread aggressively flush the bypass queue. Reviewed-by: Frederic Weisbecker Signed-off-by: Joel Fernandes

rcu/nocb: Consolidate rcu_nocb_cpu_offload/deoffload functions

2026-03-30T19:48:14Z

The rcu_nocb_cpu_offload() and rcu_nocb_cpu_deoffload() functions are nearly duplicates. Therefore, extract the common logic into rcu_nocb_cpu_toggle_offload() which takes an 'offload' boolean, and make both exported functions simple wrappers. This eliminates a bunch of duplicate code at the call sites, namely mutex locking, CPU hotplug locking and CPU online checks. Reviewed-by: Frederic Weisbecker Signed-off-by: Joel Fernandes

rcu-tasks: Remove unnecessary smp_store_release() in cblist_init_generic()

2026-03-30T19:48:14Z

The cblist_init_generic() is executed during the CPU early boot phase due to commit:30ef09635b9e ("rcu-tasks: Initialize callback lists at rcu_init() time"), at this time, only one boot CPU is online and the irq is disabled. this commit therefore use routine assignment replace of smp_store_release() and WRITE_ONCE() in the cblist_init_generic(). Signed-off-by: Zqiang Reviewed-by: Paul E. McKenney Reviewed-by: Frederic Weisbecker Signed-off-by: Joel Fernandes

rcuscale: Ditch rcu_scale_shutdown in favor of torture_shutdown_init()

2026-03-30T19:48:13Z

The torture_shutdown_init() function spawns a shutdown kthread in a manner very similar to that implemented by rcu_scale_shutdown(). This commit therefore re-implements rcu_scale_shutdown() in terms of torture_shutdown_init(). This patch was generated by Claude given as input the patch making the same transformation of ref_scale_shutdown(). Signed-off-by: Paul E. McKenney Signed-off-by: Joel Fernandes

refscale: Ditch ref_scale_shutdown in favor of torture_shutdown_init()

2026-03-30T19:48:13Z

The torture_shutdown_init() function spawns a shutdown kthread in a manner very similar to that implemented by ref_scale_shutdown(). This commit therefore re-implements ref_scale_shutdown in terms of torture_shutdown_init(). The initial draft of this patch was generated by version 2.1.16 of the Claude AI/LLM, but trained and configured for use by my employer, and prompted to refer to Linux-kernel source code. This initial draft failed to provide a forward reference to ref_scale_cleanup(), passed zero to torture_shutdown_init() for an unwelcome insta-shutdown, and failed to pass the kvm.sh --duration argument in as a refscale module parameter. On the other hand, it did catch the need to NULL main_task on the post-test self-shutdown code path, which I might well have forgotten to do. This version of the patch fixes those problems, and in fact very little of the initial draft remains. Signed-off-by: Paul E. McKenney Signed-off-by: Joel Fernandes

rcutorture: Add a textbook-style trivial preemptible RCU

2026-03-30T19:48:13Z

This commit adds a trivial textbook implementation of preemptible RCU to rcutorture ("torture_type=trivial-preempt"), similar in spirit to the existing "torture_type=trivial" textbook implementation of non-preemptible RCU. Neither trivial RCU implementation has any value for production use, and are intended only to keep Paul honest in his introductory writings and presentations. [ paulmck: Apply kernel test robot feedback. ] Signed-off-by: Joel Fernandes

srcu: Use irq_work to start GP in tiny SRCU

2026-03-25T16:00:05Z

Tiny SRCU's srcu_gp_start_if_needed() directly calls schedule_work(), which acquires the workqueue pool->lock. This causes a lockdep splat when call_srcu() is called with a scheduler lock held, due to: call_srcu() [holding pi_lock] srcu_gp_start_if_needed() schedule_work() -> pool->lock workqueue_init() / create_worker() [holding pool->lock] wake_up_process() -> try_to_wake_up() -> pi_lock Also add irq_work_sync() to cleanup_srcu_struct() to prevent a use-after-free if a queued irq_work fires after cleanup begins. Tested with rcutorture SRCU-T and no lockdep warnings. [ Thanks to Boqun for similar fix in patch "rcu: Use an intermediate irq_work to start process_srcu()" ] Signed-off-by: Joel Fernandes Reviewed-by: Paul E. McKenney Signed-off-by: Boqun Feng