cregit-Linux how code gets into the kernel

Release 4.15 kernel/task_work.c

Directory: kernel
// SPDX-License-Identifier: GPL-2.0
#include <linux/spinlock.h>
#include <linux/task_work.h>
#include <linux/tracehook.h>

static struct callback_head work_exited; 
/* all we need is ->next == NULL */

 * task_work_add - ask the @task to execute @work->func()
 * @task: the task which should run the callback
 * @work: the callback to run
 * @notify: send the notification if true
 * Queue @work for task_work_run() below and notify the @task if @notify.
 * Fails if the @task is exiting/exited and thus it can't process this @work.
 * Otherwise @work->func() will be called when the @task returns from kernel
 * mode or exits.
 * This is like the signal handler which runs in kernel mode, but it doesn't
 * try to wake up the @task.
 * Note: there is no ordering guarantee on works queued here.
 * 0 if succeeds or -ESRCH.

int task_work_add(struct task_struct *task, struct callback_head *work, bool notify) { struct callback_head *head; do { head = READ_ONCE(task->task_works); if (unlikely(head == &work_exited)) return -ESRCH; work->next = head; } while (cmpxchg(&task->task_works, head, work) != head); if (notify) set_notify_resume(task); return 0; }


Oleg Nesterov7083.33%457.14%
Al Viro1416.67%342.86%

/** * task_work_cancel - cancel a pending work added by task_work_add() * @task: the task which should execute the work * @func: identifies the work to remove * * Find the last queued pending work with ->func == @func and remove * it from queue. * * RETURNS: * The found work or NULL if not found. */
struct callback_head * task_work_cancel(struct task_struct *task, task_work_func_t func) { struct callback_head **pprev = &task->task_works; struct callback_head *work; unsigned long flags; if (likely(!task->task_works)) return NULL; /* * If cmpxchg() fails we continue without updating pprev. * Either we raced with task_work_add() which added the * new entry before this work, we will find it again. Or * we raced with task_work_run(), *pprev == NULL/exited. */ raw_spin_lock_irqsave(&task->pi_lock, flags); while ((work = READ_ONCE(*pprev))) { if (work->func != func) pprev = &work->next; else if (cmpxchg(pprev, work, work->next) == work) break; } raw_spin_unlock_irqrestore(&task->pi_lock, flags); return work; }


Oleg Nesterov10286.44%457.14%
Al Viro1512.71%228.57%
Will Deacon10.85%114.29%

/** * task_work_run - execute the works added by task_work_add() * * Flush the pending works. Should be used by the core kernel code. * Called before the task returns to the user-mode or stops, or when * it exits. In the latter case task_work_add() can no longer add the * new work after task_work_run() returns. */
void task_work_run(void) { struct task_struct *task = current; struct callback_head *work, *head, *next; for (;;) { /* * work->func() can do task_work_add(), do not set * work_exited unless the list is empty. */ raw_spin_lock_irq(&task->pi_lock); do { work = READ_ONCE(task->task_works); head = !work && (task->flags & PF_EXITING) ? &work_exited : NULL; } while (cmpxchg(&task->task_works, work, head) != work); raw_spin_unlock_irq(&task->pi_lock); if (!work) break; do { next = work->next; work->func(work); work = next; cond_resched(); } while (work); } }


Oleg Nesterov11991.54%555.56%
Al Viro86.15%333.33%
Eric Dumazet32.31%111.11%

Overall Contributors

Oleg Nesterov30887.75%642.86%
Al Viro3710.54%428.57%
Eric Dumazet41.14%214.29%
Will Deacon10.28%17.14%
Greg Kroah-Hartman10.28%17.14%
Directory: kernel
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