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authorLinus Torvalds <torvalds@linux-foundation.org>2022-08-02 19:12:45 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2022-08-02 19:12:45 -0700
commit7d9d077c783e33995c80d8b28fea1a98161934f4 (patch)
tree5404e84d237b764a07aaf299d175c1dcfbad9966 /kernel/sched/core.c
parentc2a24a7a036b3bd3a2e6c66730dfc777cae6540a (diff)
parent34bc7b454dc31f75a0be7ee8ab378135523d7c51 (diff)
downloadlinux-7d9d077c783e33995c80d8b28fea1a98161934f4.tar.bz2
Merge tag 'rcu.2022.07.26a' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu
Pull RCU updates from Paul McKenney: - Documentation updates - Miscellaneous fixes - Callback-offload updates, perhaps most notably a new RCU_NOCB_CPU_DEFAULT_ALL Kconfig option that causes all CPUs to be offloaded at boot time, regardless of kernel boot parameters. This is useful to battery-powered systems such as ChromeOS and Android. In addition, a new RCU_NOCB_CPU_CB_BOOST kernel boot parameter prevents offloaded callbacks from interfering with real-time workloads and with energy-efficiency mechanisms - Polled grace-period updates, perhaps most notably making these APIs account for both normal and expedited grace periods - Tasks RCU updates, perhaps most notably reducing the CPU overhead of RCU tasks trace grace periods by more than a factor of two on a system with 15,000 tasks. The reduction is expected to increase with the number of tasks, so it seems reasonable to hypothesize that a system with 150,000 tasks might see a 20-fold reduction in CPU overhead - Torture-test updates - Updates that merge RCU's dyntick-idle tracking into context tracking, thus reducing the overhead of transitioning to kernel mode from either idle or nohz_full userspace execution for kernels that track context independently of RCU. This is expected to be helpful primarily for kernels built with CONFIG_NO_HZ_FULL=y * tag 'rcu.2022.07.26a' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu: (98 commits) rcu: Add irqs-disabled indicator to expedited RCU CPU stall warnings rcu: Diagnose extended sync_rcu_do_polled_gp() loops rcu: Put panic_on_rcu_stall() after expedited RCU CPU stall warnings rcutorture: Test polled expedited grace-period primitives rcu: Add polled expedited grace-period primitives rcutorture: Verify that polled GP API sees synchronous grace periods rcu: Make Tiny RCU grace periods visible to polled APIs rcu: Make polled grace-period API account for expedited grace periods rcu: Switch polled grace-period APIs to ->gp_seq_polled rcu/nocb: Avoid polling when my_rdp->nocb_head_rdp list is empty rcu/nocb: Add option to opt rcuo kthreads out of RT priority rcu: Add nocb_cb_kthread check to rcu_is_callbacks_kthread() rcu/nocb: Add an option to offload all CPUs on boot rcu/nocb: Fix NOCB kthreads spawn failure with rcu_nocb_rdp_deoffload() direct call rcu/nocb: Invert rcu_state.barrier_mutex VS hotplug lock locking order rcu/nocb: Add/del rdp to iterate from rcuog itself rcu/tree: Add comment to describe GP-done condition in fqs loop rcu: Initialize first_gp_fqs at declaration in rcu_gp_fqs() rcu/kvfree: Remove useless monitor_todo flag rcu: Cleanup RCU urgency state for offline CPU ...
Diffstat (limited to 'kernel/sched/core.c')
-rw-r--r--kernel/sched/core.c34
1 files changed, 33 insertions, 1 deletions
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index a1143acbf7a0..189999007f32 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4263,6 +4263,38 @@ int task_call_func(struct task_struct *p, task_call_f func, void *arg)
}
/**
+ * cpu_curr_snapshot - Return a snapshot of the currently running task
+ * @cpu: The CPU on which to snapshot the task.
+ *
+ * Returns the task_struct pointer of the task "currently" running on
+ * the specified CPU. If the same task is running on that CPU throughout,
+ * the return value will be a pointer to that task's task_struct structure.
+ * If the CPU did any context switches even vaguely concurrently with the
+ * execution of this function, the return value will be a pointer to the
+ * task_struct structure of a randomly chosen task that was running on
+ * that CPU somewhere around the time that this function was executing.
+ *
+ * If the specified CPU was offline, the return value is whatever it
+ * is, perhaps a pointer to the task_struct structure of that CPU's idle
+ * task, but there is no guarantee. Callers wishing a useful return
+ * value must take some action to ensure that the specified CPU remains
+ * online throughout.
+ *
+ * This function executes full memory barriers before and after fetching
+ * the pointer, which permits the caller to confine this function's fetch
+ * with respect to the caller's accesses to other shared variables.
+ */
+struct task_struct *cpu_curr_snapshot(int cpu)
+{
+ struct task_struct *t;
+
+ smp_mb(); /* Pairing determined by caller's synchronization design. */
+ t = rcu_dereference(cpu_curr(cpu));
+ smp_mb(); /* Pairing determined by caller's synchronization design. */
+ return t;
+}
+
+/**
* wake_up_process - Wake up a specific process
* @p: The process to be woken up.
*
@@ -6563,7 +6595,7 @@ void __sched schedule_idle(void)
} while (need_resched());
}
-#if defined(CONFIG_CONTEXT_TRACKING) && !defined(CONFIG_HAVE_CONTEXT_TRACKING_OFFSTACK)
+#if defined(CONFIG_CONTEXT_TRACKING_USER) && !defined(CONFIG_HAVE_CONTEXT_TRACKING_USER_OFFSTACK)
asmlinkage __visible void __sched schedule_user(void)
{
/*