linux/kernel/rcu, branch v6.15

treewide: Switch/rename to timer_delete[_sync]()

2025-04-05T08:30:12Z

timer_delete[_sync]() replaces del_timer[_sync](). Convert the whole tree over and remove the historical wrapper inlines. Conversion was done with coccinelle plus manual fixups where necessary. Signed-off-by: Thomas Gleixner Signed-off-by: Ingo Molnar

Merge tag 'rcu-fixes-v6.15' of git://git.kernel.org/pub/scm/linux/kernel/git/rcu/linux

2025-04-02T17:04:48Z

Pull RCU fix from Boqun Feng: - srcu: Make FORCE_NEED_SRCU_NMI_SAFE depend on RCU_EXPERT * tag 'rcu-fixes-v6.15' of git://git.kernel.org/pub/scm/linux/kernel/git/rcu/linux: srcu: Make FORCE_NEED_SRCU_NMI_SAFE depend on RCU_EXPERT

srcu: Make FORCE_NEED_SRCU_NMI_SAFE depend on RCU_EXPERT

2025-03-29T04:19:17Z

The FORCE_NEED_SRCU_NMI_SAFE is useful only for those wishing to test the SRCU code paths that accommodate architectures that do not have NMI-safe per-CPU operations, that is, those architectures that do not select the ARCH_HAS_NMI_SAFE_THIS_CPU_OPS Kconfig option. As such, this is a specialized Kconfig option that is not intended for casual users. This commit therefore hides it behind the RCU_EXPERT Kconfig option. Given that this new FORCE_NEED_SRCU_NMI_SAFE Kconfig option has no effect unless the ARCH_HAS_NMI_SAFE_THIS_CPU_OPS Kconfig option is also selected, it also depends on this Kconfig option. [ paulmck: Apply Geert Uytterhoeven feedback. ] [ boqun: Add the "Fixes" tag. ] Reported-by: Geert Uytterhoeven Closes: https://lore.kernel.org/all/CAMuHMdX6dy9_tmpLkpcnGzxyRbe6qSWYukcPp=H1GzZdyd3qBQ@mail.gmail.com/ Fixes: 536e8b9b80bc ("srcu: Add FORCE_NEED_SRCU_NMI_SAFE Kconfig for testing") Signed-off-by: Paul E. McKenney Reviewed-by: Geert Uytterhoeven Signed-off-by: Boqun Feng

Merge tag 'rcu-next-v6.15' of git://git.kernel.org/pub/scm/linux/kernel/git/rcu/linux

2025-03-25T02:41:37Z

Pull RCU updates from Boqun Feng: "Documentation: - Add broken-timing possibility to stallwarn.rst - Improve discussion of this_cpu_ptr(), add raw_cpu_ptr() - Document self-propagating callbacks - Point call_srcu() to call_rcu() for detailed memory ordering - Add CONFIG_RCU_LAZY delays to call_rcu() kernel-doc header - Clarify RCU_LAZY and RCU_LAZY_DEFAULT_OFF help text - Remove references to old grace-period-wait primitives srcu: - Introduce srcu_read_{un,}lock_fast(), which is similar to srcu_read_{un,}lock_lite(): avoid smp_mb()s in lock and unlock at the cost of calling synchronize_rcu() in synchronize_srcu() Moreover, by returning the percpu offset of the counter at srcu_read_lock_fast() time, srcu_read_unlock_fast() can avoid extra pointer dereferencing, which makes it faster than srcu_read_{un,}lock_lite() srcu_read_{un,}lock_fast() are intended to replace rcu_read_{un,}lock_trace() if possible RCU torture: - Add get_torture_init_jiffies() to return the start time of the test - Add a test_boost_holdoff module parameter to allow delaying boosting tests when building rcutorture as built-in - Add grace period sequence number logging at the beginning and end of failure/close-call results - Switch to hexadecimal for the expedited grace period sequence number in the rcu_exp_grace_period trace point - Make cur_ops->format_gp_seqs take buffer length - Move RCU_TORTURE_TEST_{CHK_RDR_STATE,LOG_CPU} to bool - Complain when invalid SRCU reader_flavor is specified - Add FORCE_NEED_SRCU_NMI_SAFE Kconfig for testing, which forces SRCU uses atomics even when percpu ops are NMI safe, and use the Kconfig for SRCU lockdep testing Misc: - Split rcu_report_exp_cpu_mult() mask parameter and use for tracing - Remove READ_ONCE() for rdp->gpwrap access in __note_gp_changes() - Fix get_state_synchronize_rcu_full() GP-start detection - Move RCU Tasks self-tests to core_initcall() - Print segment lengths in show_rcu_nocb_gp_state() - Make RCU watch ct_kernel_exit_state() warning - Flush console log from kernel_power_off() - rcutorture: Allow a negative value for nfakewriters - rcu: Update TREE05.boot to test normal synchronize_rcu() - rcu: Use _full() API to debug synchronize_rcu() Make RCU handle PREEMPT_LAZY better: - Fix header guard for rcu_all_qs() - rcu: Rename PREEMPT_AUTO to PREEMPT_LAZY - Update __cond_resched comment about RCU quiescent states - Handle unstable rdp in rcu_read_unlock_strict() - Handle quiescent states for PREEMPT_RCU=n, PREEMPT_COUNT=y - osnoise: Provide quiescent states - Adjust rcutorture with possible PREEMPT_RCU=n && PREEMPT_COUNT=y combination - Limit PREEMPT_RCU configurations - Make rcutorture senario TREE07 and senario TREE10 use PREEMPT_LAZY=y" * tag 'rcu-next-v6.15' of git://git.kernel.org/pub/scm/linux/kernel/git/rcu/linux: (59 commits) rcutorture: Make scenario TREE07 build CONFIG_PREEMPT_LAZY=y rcutorture: Make scenario TREE10 build CONFIG_PREEMPT_LAZY=y rcu: limit PREEMPT_RCU configurations rcutorture: Update ->extendables check for lazy preemption rcutorture: Update rcutorture_one_extend_check() for lazy preemption osnoise: provide quiescent states rcu: Use _full() API to debug synchronize_rcu() rcu: Update TREE05.boot to test normal synchronize_rcu() rcutorture: Allow a negative value for nfakewriters Flush console log from kernel_power_off() context_tracking: Make RCU watch ct_kernel_exit_state() warning rcu/nocb: Print segment lengths in show_rcu_nocb_gp_state() rcu-tasks: Move RCU Tasks self-tests to core_initcall() rcu: Fix get_state_synchronize_rcu_full() GP-start detection torture: Make SRCU lockdep testing use srcu_read_lock_nmisafe() srcu: Add FORCE_NEED_SRCU_NMI_SAFE Kconfig for testing rcutorture: Complain when invalid SRCU reader_flavor is specified rcutorture: Move RCU_TORTURE_TEST_{CHK_RDR_STATE,LOG_CPU} to bool rcutorture: Make cur_ops->format_gp_seqs take buffer length rcutorture: Add ftrace-compatible timestamp to GP# failure/close-call output ...

Merge branches 'docs.2025.02.04a', 'lazypreempt.2025.03.04a', 'misc.2025.03.04a', 'srcu.2025.02.05a' and 'torture.2025.02.05a'

2025-03-05T02:47:32Z

rcu: limit PREEMPT_RCU configurations

2025-03-05T02:46:47Z

PREEMPT_LAZY can be enabled stand-alone or alongside PREEMPT_DYNAMIC which allows for dynamic switching of preemption models. The choice of PREEMPT_RCU or not, however, is fixed at compile time. Given that PREEMPT_RCU makes some trade-offs to optimize for latency as opposed to throughput, configurations with limited preemption might prefer the stronger forward-progress guarantees of PREEMPT_RCU=n. Accordingly, explicitly limit PREEMPT_RCU=y to the latency oriented preemption models: PREEMPT, PREEMPT_RT, and the runtime configurable model PREEMPT_DYNAMIC. This means the throughput oriented models, PREEMPT_NONE, PREEMPT_VOLUNTARY, and PREEMPT_LAZY will run with PREEMPT_RCU=n. Cc: Paul E. McKenney Cc: Peter Zijlstra Reviewed-by: Frederic Weisbecker Signed-off-by: Ankur Arora Signed-off-by: Paul E. McKenney Signed-off-by: Boqun Feng

rcutorture: Update ->extendables check for lazy preemption

2025-03-05T02:46:47Z

The rcutorture_one_extend_check() function's second last check assumes that "preempt_count() & PREEMPT_MASK" is non-zero only if RCUTORTURE_RDR_PREEMPT or RCUTORTURE_RDR_SCHED bit is set. This works for preemptible RCU and for non-preemptible RCU running in a non-preemptible kernel. But it fails for non-preemptible RCU running in a preemptible kernel because then rcu_read_lock() is just preempt_disable(), which increases preempt count. This commit therefore adjusts this check to take into account the case fo non-preemptible RCU running in a preemptible kernel. Reviewed-by: Paul E. McKenney Signed-off-by: Boqun Feng

rcutorture: Update rcutorture_one_extend_check() for lazy preemption

2025-03-05T02:46:46Z

The rcutorture_one_extend_check() function's last check assumes that if cur_ops->readlock_nesting() returns greater than zero, either the RCUTORTURE_RDR_RCU_1 or the RCUTORTURE_RDR_RCU_2 bit must be set, that is, there must be at least one rcu_read_lock() in effect. This works for preemptible RCU and for non-preemptible RCU running in a non-preemptible kernel. But it fails for non-preemptible RCU running in a preemptible kernel because then RCU's cur_ops->readlock_nesting() function, which is rcu_torture_readlock_nesting(), will return the PREEMPT_MASK mask bits from preempt_count(). The result will be greater than zero if preemption is disabled, including by the RCUTORTURE_RDR_PREEMPT and RCUTORTURE_RDR_SCHED bits. This commit therefore adjusts this check to take into account the case fo non-preemptible RCU running in a preemptible kernel. [boqun: Fix the if condition and add comment] Reported-by: kernel test robot Closes: https://lore.kernel.org/oe-lkp/202502171415.8ec87c87-lkp@intel.com Co-developed-by: Boqun Feng Signed-off-by: Boqun Feng Co-developed-by: Joel Fernandes Signed-off-by: Joel Fernandes Signed-off-by: Paul E. McKenney Tested-by: kernel test robot Signed-off-by: Boqun Feng

rcu: Use _full() API to debug synchronize_rcu()

2025-03-05T02:44:29Z

Switch for using of get_state_synchronize_rcu_full() and poll_state_synchronize_rcu_full() pair to debug a normal synchronize_rcu() call. Just using "not" full APIs to identify if a grace period is passed or not might lead to a false-positive kernel splat. It can happen, because get_state_synchronize_rcu() compresses both normal and expedited states into one single unsigned long value, so a poll_state_synchronize_rcu() can miss GP-completion when synchronize_rcu()/synchronize_rcu_expedited() concurrently run. To address this, switch to poll_state_synchronize_rcu_full() and get_state_synchronize_rcu_full() APIs, which use separate variables for expedited and normal states. Reported-by: cheung wall Closes: https://lore.kernel.org/lkml/Z5ikQeVmVdsWQrdD@pc636/T/ Fixes: 988f569ae041 ("rcu: Reduce synchronize_rcu() latency") Signed-off-by: Uladzislau Rezki (Sony) Reviewed-by: Paul E. McKenney Link: https://lore.kernel.org/r/20250227131613.52683-3-urezki@gmail.com Signed-off-by: Boqun Feng

rcutorture: Allow a negative value for nfakewriters

2025-03-05T02:44:29Z

Currently "nfakewriters" parameter can be set to any value but there is no possibility to adjust it automatically based on how many CPUs a system has where a test is run on. To address this, if the "nfakewriters" is set to negative it will be adjusted to num_online_cpus() during torture initialization. Reviewed-by: Paul E. McKenney Signed-off-by: Uladzislau Rezki (Sony) Link: https://lore.kernel.org/r/20250227131613.52683-1-urezki@gmail.com Signed-off-by: Boqun Feng