user/sven/linux.git/kernel/rcu/tree.c, branch v5.4.249

rcu: Fix __this_cpu_read() lockdep warning in rcu_force_quiescent_state()

2023-01-18T10:41:33Z

[ Upstream commit ceb1c8c9b8aa9199da46a0f29d2d5f08d9b44c15 ] Running rcutorture with non-zero fqs_duration module parameter in a kernel built with CONFIG_PREEMPTION=y results in the following splat: BUG: using __this_cpu_read() in preemptible [00000000] code: rcu_torture_fqs/398 caller is __this_cpu_preempt_check+0x13/0x20 CPU: 3 PID: 398 Comm: rcu_torture_fqs Not tainted 6.0.0-rc1-yoctodev-standard+ Call Trace: dump_stack_lvl+0x5b/0x86 dump_stack+0x10/0x16 check_preemption_disabled+0xe5/0xf0 __this_cpu_preempt_check+0x13/0x20 rcu_force_quiescent_state.part.0+0x1c/0x170 rcu_force_quiescent_state+0x1e/0x30 rcu_torture_fqs+0xca/0x160 ? rcu_torture_boost+0x430/0x430 kthread+0x192/0x1d0 ? kthread_complete_and_exit+0x30/0x30 ret_from_fork+0x22/0x30 The problem is that rcu_force_quiescent_state() uses __this_cpu_read() in preemptible code instead of the proper raw_cpu_read(). This commit therefore changes __this_cpu_read() to raw_cpu_read(). Signed-off-by: Zqiang Reviewed-by: Joel Fernandes (Google) Signed-off-by: Paul E. McKenney Signed-off-by: Sasha Levin

rcu: Tighten rcu_advance_cbs_nowake() checks

2022-01-29T09:25:09Z

commit 614ddad17f22a22e035e2ea37a04815f50362017 upstream. Currently, rcu_advance_cbs_nowake() checks that a grace period is in progress, however, that grace period could end just after the check. This commit rechecks that a grace period is still in progress while holding the rcu_node structure's lock. The grace period cannot end while the current CPU's rcu_node structure's ->lock is held, thus avoiding false positives from the WARN_ON_ONCE(). As Daniel Vacek noted, it is not necessary for the rcu_node structure to have a CPU that has not yet passed through its quiescent state. Tested-by: Guillaume Morin Signed-off-by: Paul E. McKenney Signed-off-by: Greg Kroah-Hartman

rcu: Mark accesses to rcu_state.n_force_qs

2021-12-22T08:29:40Z

commit 2431774f04d1050292054c763070021bade7b151 upstream. This commit marks accesses to the rcu_state.n_force_qs. These data races are hard to make happen, but syzkaller was equal to the task. Reported-by: syzbot+e08a83a1940ec3846cd5@syzkaller.appspotmail.com Acked-by: Marco Elver Signed-off-by: Paul E. McKenney Signed-off-by: Greg Kroah-Hartman

srcu: Fix broken node geometry after early ssp init

2021-07-20T14:10:41Z

[ Upstream commit b5befe842e6612cf894cf4a199924ee872d8b7d8 ] An srcu_struct structure that is initialized before rcu_init_geometry() will have its srcu_node hierarchy based on CONFIG_NR_CPUS. Once rcu_init_geometry() is called, this hierarchy is compressed as needed for the actual maximum number of CPUs for this system. Later on, that srcu_struct structure is confused, sometimes referring to its initial CONFIG_NR_CPUS-based hierarchy, and sometimes instead to the new num_possible_cpus() hierarchy. For example, each of its ->mynode fields continues to reference the original leaf rcu_node structures, some of which might no longer exist. On the other hand, srcu_for_each_node_breadth_first() traverses to the new node hierarchy. There are at least two bad possible outcomes to this: 1) a) A callback enqueued early on an srcu_data structure (call it *sdp) is recorded pending on sdp->mynode->srcu_data_have_cbs in srcu_funnel_gp_start() with sdp->mynode pointing to a deep leaf (say 3 levels). b) The grace period ends after rcu_init_geometry() shrinks the nodes level to a single one. srcu_gp_end() walks through the new srcu_node hierarchy without ever reaching the old leaves so the callback is never executed. This is easily reproduced on an 8 CPUs machine with CONFIG_NR_CPUS >= 32 and "rcupdate.rcu_self_test=1". The srcu_barrier() after early tests verification never completes and the boot hangs: [ 5413.141029] INFO: task swapper/0:1 blocked for more than 4915 seconds. [ 5413.147564] Not tainted 5.12.0-rc4+ #28 [ 5413.151927] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. [ 5413.159753] task:swapper/0 state:D stack: 0 pid: 1 ppid: 0 flags:0x00004000 [ 5413.168099] Call Trace: [ 5413.170555] __schedule+0x36c/0x930 [ 5413.174057] ? wait_for_completion+0x88/0x110 [ 5413.178423] schedule+0x46/0xf0 [ 5413.181575] schedule_timeout+0x284/0x380 [ 5413.185591] ? wait_for_completion+0x88/0x110 [ 5413.189957] ? mark_held_locks+0x61/0x80 [ 5413.193882] ? mark_held_locks+0x61/0x80 [ 5413.197809] ? _raw_spin_unlock_irq+0x24/0x50 [ 5413.202173] ? wait_for_completion+0x88/0x110 [ 5413.206535] wait_for_completion+0xb4/0x110 [ 5413.210724] ? srcu_torture_stats_print+0x110/0x110 [ 5413.215610] srcu_barrier+0x187/0x200 [ 5413.219277] ? rcu_tasks_verify_self_tests+0x50/0x50 [ 5413.224244] ? rdinit_setup+0x2b/0x2b [ 5413.227907] rcu_verify_early_boot_tests+0x2d/0x40 [ 5413.232700] do_one_initcall+0x63/0x310 [ 5413.236541] ? rdinit_setup+0x2b/0x2b [ 5413.240207] ? rcu_read_lock_sched_held+0x52/0x80 [ 5413.244912] kernel_init_freeable+0x253/0x28f [ 5413.249273] ? rest_init+0x250/0x250 [ 5413.252846] kernel_init+0xa/0x110 [ 5413.256257] ret_from_fork+0x22/0x30 2) An srcu_struct structure that is initialized before rcu_init_geometry() and used afterward will always have stale rdp->mynode references, resulting in callbacks to be missed in srcu_gp_end(), just like in the previous scenario. This commit therefore causes init_srcu_struct_nodes to initialize the geometry, if needed. This ensures that the srcu_node hierarchy is properly built and distributed from the get-go. Suggested-by: Paul E. McKenney Signed-off-by: Frederic Weisbecker Cc: Boqun Feng Cc: Lai Jiangshan Cc: Neeraj Upadhyay Cc: Josh Triplett Cc: Joel Fernandes Cc: Uladzislau Rezki Signed-off-by: Paul E. McKenney Signed-off-by: Sasha Levin

rcu: Invoke rcu_spawn_core_kthreads() from rcu_spawn_gp_kthread()

2021-07-14T14:53:36Z

[ Upstream commit 8e4b1d2bc198e34b48fc7cc3a3c5a2fcb269e271 ] Currently, rcu_spawn_core_kthreads() is invoked via an early_initcall(), which works, except that rcu_spawn_gp_kthread() is also invoked via an early_initcall() and rcu_spawn_core_kthreads() relies on adjustments to kthread_prio that are carried out by rcu_spawn_gp_kthread(). There is no guaranttee of ordering among early_initcall() handlers, and thus no guarantee that kthread_prio will be properly checked and range-limited at the time that rcu_spawn_core_kthreads() needs it. In most cases, this bug is harmless. After all, the only reason that rcu_spawn_gp_kthread() adjusts the value of kthread_prio is if the user specified a nonsensical value for this boot parameter, which experience indicates is rare. Nevertheless, a bug is a bug. This commit therefore causes the rcu_spawn_core_kthreads() function to be invoked directly from rcu_spawn_gp_kthread() after any needed adjustments to kthread_prio have been carried out. Fixes: 48d07c04b4cc ("rcu: Enable elimination of Tree-RCU softirq processing") Signed-off-by: Paul E. McKenney Signed-off-by: Sasha Levin

rcu/nocb: Perform deferred wake up before last idle's need_resched() check

2021-03-04T09:26:47Z

commit 43789ef3f7d61aa7bed0cb2764e588fc990c30ef upstream. Entering RCU idle mode may cause a deferred wake up of an RCU NOCB_GP kthread (rcuog) to be serviced. Usually a local wake up happening while running the idle task is handled in one of the need_resched() checks carefully placed within the idle loop that can break to the scheduler. Unfortunately the call to rcu_idle_enter() is already beyond the last generic need_resched() check and we may halt the CPU with a resched request unhandled, leaving the task hanging. Fix this with splitting the rcuog wakeup handling from rcu_idle_enter() and place it before the last generic need_resched() check in the idle loop. It is then assumed that no call to call_rcu() will be performed after that in the idle loop until the CPU is put in low power mode. Fixes: 96d3fd0d315a (rcu: Break call_rcu() deadlock involving scheduler and perf) Reported-by: Paul E. McKenney Signed-off-by: Frederic Weisbecker Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Ingo Molnar Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/20210131230548.32970-3-frederic@kernel.org Signed-off-by: Greg Kroah-Hartman

rcu: Pull deferred rcuog wake up to rcu_eqs_enter() callers

2021-03-04T09:26:46Z

commit 54b7429efffc99e845ba9381bee3244f012a06c2 upstream. Deferred wakeup of rcuog kthreads upon RCU idle mode entry is going to be handled differently whether initiated by idle, user or guest. Prepare with pulling that control up to rcu_eqs_enter() callers. Signed-off-by: Frederic Weisbecker Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Ingo Molnar Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/20210131230548.32970-2-frederic@kernel.org Signed-off-by: Greg Kroah-Hartman

arm64: smp: Tell RCU about CPUs that fail to come online

2020-11-24T12:29:01Z

[ Upstream commit 04e613ded8c26489b3e0f9101b44462f780d1a35 ] Commit ce3d31ad3cac ("arm64/smp: Move rcu_cpu_starting() earlier") ensured that RCU is informed early about incoming CPUs that might end up calling into printk() before they are online. However, if such a CPU fails the early CPU feature compatibility checks in check_local_cpu_capabilities(), then it will be powered off or parked without informing RCU, leading to an endless stream of stalls: | rcu: INFO: rcu_preempt detected stalls on CPUs/tasks: | rcu: 2-O...: (0 ticks this GP) idle=002/1/0x4000000000000000 softirq=0/0 fqs=2593 | (detected by 0, t=5252 jiffies, g=9317, q=136) | Task dump for CPU 2: | task:swapper/2 state:R running task stack: 0 pid: 0 ppid: 1 flags:0x00000028 | Call trace: | ret_from_fork+0x0/0x30 Ensure that the dying CPU invokes rcu_report_dead() prior to being powered off or parked. Cc: Qian Cai Cc: "Paul E. McKenney" Reviewed-by: Paul E. McKenney Suggested-by: Qian Cai Link: https://lore.kernel.org/r/20201105222242.GA8842@willie-the-truck Link: https://lore.kernel.org/r/20201106103602.9849-3-will@kernel.org Signed-off-by: Will Deacon Signed-off-by: Sasha Levin

rcu: Fix data-race due to atomic_t copy-by-value

2020-02-24T07:36:23Z

[ Upstream commit 6cf539a87a61a4fbc43f625267dbcbcf283872ed ] This fixes a data-race where `atomic_t dynticks` is copied by value. The copy is performed non-atomically, resulting in a data-race if `dynticks` is updated concurrently. This data-race was found with KCSAN: ================================================================== BUG: KCSAN: data-race in dyntick_save_progress_counter / rcu_irq_enter write to 0xffff989dbdbe98e0 of 4 bytes by task 10 on cpu 3: atomic_add_return include/asm-generic/atomic-instrumented.h:78 [inline] rcu_dynticks_snap kernel/rcu/tree.c:310 [inline] dyntick_save_progress_counter+0x43/0x1b0 kernel/rcu/tree.c:984 force_qs_rnp+0x183/0x200 kernel/rcu/tree.c:2286 rcu_gp_fqs kernel/rcu/tree.c:1601 [inline] rcu_gp_fqs_loop+0x71/0x880 kernel/rcu/tree.c:1653 rcu_gp_kthread+0x22c/0x3b0 kernel/rcu/tree.c:1799 kthread+0x1b5/0x200 kernel/kthread.c:255 read to 0xffff989dbdbe98e0 of 4 bytes by task 154 on cpu 7: rcu_nmi_enter_common kernel/rcu/tree.c:828 [inline] rcu_irq_enter+0xda/0x240 kernel/rcu/tree.c:870 irq_enter+0x5/0x50 kernel/softirq.c:347 Reported by Kernel Concurrency Sanitizer on: CPU: 7 PID: 154 Comm: kworker/7:1H Not tainted 5.3.0+ #5 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1 04/01/2014 Workqueue: kblockd blk_mq_run_work_fn ================================================================== Signed-off-by: Marco Elver Cc: Paul E. McKenney Cc: Josh Triplett Cc: Steven Rostedt Cc: Mathieu Desnoyers Cc: Joel Fernandes Cc: Ingo Molnar Cc: Dmitry Vyukov Cc: rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org Reviewed-by: Joel Fernandes (Google) Signed-off-by: Paul E. McKenney Signed-off-by: Sasha Levin

Merge branch 'sched-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2019-09-17T00:25:49Z

Pull scheduler updates from Ingo Molnar: - MAINTAINERS: Add Mark Rutland as perf submaintainer, Juri Lelli and Vincent Guittot as scheduler submaintainers. Add Dietmar Eggemann, Steven Rostedt, Ben Segall and Mel Gorman as scheduler reviewers. As perf and the scheduler is getting bigger and more complex, document the status quo of current responsibilities and interests, and spread the review pain^H^H^H^H fun via an increase in the Cc: linecount generated by scripts/get_maintainer.pl. :-) - Add another series of patches that brings the -rt (PREEMPT_RT) tree closer to mainline: split the monolithic CONFIG_PREEMPT dependencies into a new CONFIG_PREEMPTION category that will allow the eventual introduction of CONFIG_PREEMPT_RT. Still a few more hundred patches to go though. - Extend the CPU cgroup controller with uclamp.min and uclamp.max to allow the finer shaping of CPU bandwidth usage. - Micro-optimize energy-aware wake-ups from O(CPUS^2) to O(CPUS). - Improve the behavior of high CPU count, high thread count applications running under cpu.cfs_quota_us constraints. - Improve balancing with SCHED_IDLE (SCHED_BATCH) tasks present. - Improve CPU isolation housekeeping CPU allocation NUMA locality. - Fix deadline scheduler bandwidth calculations and logic when cpusets rebuilds the topology, or when it gets deadline-throttled while it's being offlined. - Convert the cpuset_mutex to percpu_rwsem, to allow it to be used from setscheduler() system calls without creating global serialization. Add new synchronization between cpuset topology-changing events and the deadline acceptance tests in setscheduler(), which were broken before. - Rework the active_mm state machine to be less confusing and more optimal. - Rework (simplify) the pick_next_task() slowpath. - Improve load-balancing on AMD EPYC systems. - ... and misc cleanups, smaller fixes and improvements - please see the Git log for more details. * 'sched-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (53 commits) sched/psi: Correct overly pessimistic size calculation sched/fair: Speed-up energy-aware wake-ups sched/uclamp: Always use 'enum uclamp_id' for clamp_id values sched/uclamp: Update CPU's refcount on TG's clamp changes sched/uclamp: Use TG's clamps to restrict TASK's clamps sched/uclamp: Propagate system defaults to the root group sched/uclamp: Propagate parent clamps sched/uclamp: Extend CPU's cgroup controller sched/topology: Improve load balancing on AMD EPYC systems arch, ia64: Make NUMA select SMP sched, perf: MAINTAINERS update, add submaintainers and reviewers sched/fair: Use rq_lock/unlock in online_fair_sched_group cpufreq: schedutil: fix equation in comment sched: Rework pick_next_task() slow-path sched: Allow put_prev_task() to drop rq->lock sched/fair: Expose newidle_balance() sched: Add task_struct pointer to sched_class::set_curr_task sched: Rework CPU hotplug task selection sched/{rt,deadline}: Fix set_next_task vs pick_next_task sched: Fix kerneldoc comment for ia64_set_curr_task ...