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Date: Sun, 26 Aug 2012 21:11:32 +0200 From: Oleg Nesterov <oleg@...hat.com> To: Peter Zijlstra <peterz@...radead.org>, Al Viro <viro@...iv.linux.org.uk> Cc: Dave Jones <davej@...hat.com>, Linux Kernel <linux-kernel@...r.kernel.org>, Thomas Gleixner <tglx@...utronix.de>, rostedt <rostedt@...dmis.org>, dhowells <dhowells@...hat.com>, Linus Torvalds <torvalds@...ux-foundation.org> Subject: [PATCH 0/4] (Was: lockdep trace from posix timers) On 08/24, Oleg Nesterov wrote: > > Peter, if you think it can work for you and if you agree with > the implementation I will be happy to send the patch. I think I should try anyway ;) To simplify the review, I attached the resulting code below. Changes: - Comments. - Not sure this is really better, but task_work_run() does not need to actually take pi_lock, unlock_wait is enough. However, in this case the dummy entry is better than the fake pointer. Oleg. #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 */ int task_work_add(struct task_struct *task, struct callback_head *work, bool notify) { struct callback_head *head; do { head = ACCESS_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; } 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 = NULL; unsigned long flags; /* * 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 = ACCESS_ONCE(*pprev))) { read_barrier_depends(); 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; } 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. */ do { work = ACCESS_ONCE(task->task_works); head = !work && (task->flags & PF_EXITING) ? &work_exited : NULL; } while (cmpxchg(&task->task_works, work, head) != work); if (!work) break; /* * Synchronize with task_work_cancel(). It can't remove * the first entry == work, cmpxchg(task_works) should * fail, but it can play with *work and other entries. */ raw_spin_unlock_wait(&task->pi_lock); smp_mb(); /* Reverse the list to run the works in fifo order */ head = NULL; do { next = work->next; work->next = head; head = work; work = next; } while (work); work = head; do { next = work->next; work->func(work); work = next; cond_resched(); } while (work); } } -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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