linux/kernel/task_work.c
Oleg Nesterov e73f8959af task_work_add: generic process-context callbacks
Provide a simple mechanism that allows running code in the (nonatomic)
context of the arbitrary task.

The caller does task_work_add(task, task_work) and this task executes
task_work->func() either from do_notify_resume() or from do_exit().  The
callback can rely on PF_EXITING to detect the latter case.

"struct task_work" can be embedded in another struct, still it has "void
*data" to handle the most common/simple case.

This allows us to kill the ->replacement_session_keyring hack, and
potentially this can have more users.

Performance-wise, this adds 2 "unlikely(!hlist_empty())" checks into
tracehook_notify_resume() and do_exit().  But at the same time we can
remove the "replacement_session_keyring != NULL" checks from
arch/*/signal.c and exit_creds().

Note: task_work_add/task_work_run abuses ->pi_lock.  This is only because
this lock is already used by lookup_pi_state() to synchronize with
do_exit() setting PF_EXITING.  Fortunately the scope of this lock in
task_work.c is really tiny, and the code is unlikely anyway.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: David Howells <dhowells@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Richard Kuo <rkuo@codeaurora.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Alexander Gordeev <agordeev@redhat.com>
Cc: Chris Zankel <chris@zankel.net>
Cc: David Smith <dsmith@redhat.com>
Cc: "Frank Ch. Eigler" <fche@redhat.com>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Larry Woodman <lwoodman@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2012-05-23 22:09:21 -04:00

85 lines
2.0 KiB
C

#include <linux/spinlock.h>
#include <linux/task_work.h>
#include <linux/tracehook.h>
int
task_work_add(struct task_struct *task, struct task_work *twork, bool notify)
{
unsigned long flags;
int err = -ESRCH;
#ifndef TIF_NOTIFY_RESUME
if (notify)
return -ENOTSUPP;
#endif
/*
* We must not insert the new work if the task has already passed
* exit_task_work(). We rely on do_exit()->raw_spin_unlock_wait()
* and check PF_EXITING under pi_lock.
*/
raw_spin_lock_irqsave(&task->pi_lock, flags);
if (likely(!(task->flags & PF_EXITING))) {
hlist_add_head(&twork->hlist, &task->task_works);
err = 0;
}
raw_spin_unlock_irqrestore(&task->pi_lock, flags);
/* test_and_set_bit() implies mb(), see tracehook_notify_resume(). */
if (likely(!err) && notify)
set_notify_resume(task);
return err;
}
struct task_work *
task_work_cancel(struct task_struct *task, task_work_func_t func)
{
unsigned long flags;
struct task_work *twork;
struct hlist_node *pos;
raw_spin_lock_irqsave(&task->pi_lock, flags);
hlist_for_each_entry(twork, pos, &task->task_works, hlist) {
if (twork->func == func) {
hlist_del(&twork->hlist);
goto found;
}
}
twork = NULL;
found:
raw_spin_unlock_irqrestore(&task->pi_lock, flags);
return twork;
}
void task_work_run(void)
{
struct task_struct *task = current;
struct hlist_head task_works;
struct hlist_node *pos;
raw_spin_lock_irq(&task->pi_lock);
hlist_move_list(&task->task_works, &task_works);
raw_spin_unlock_irq(&task->pi_lock);
if (unlikely(hlist_empty(&task_works)))
return;
/*
* We use hlist to save the space in task_struct, but we want fifo.
* Find the last entry, the list should be short, then process them
* in reverse order.
*/
for (pos = task_works.first; pos->next; pos = pos->next)
;
for (;;) {
struct hlist_node **pprev = pos->pprev;
struct task_work *twork = container_of(pos, struct task_work,
hlist);
twork->func(twork);
if (pprev == &task_works.first)
break;
pos = container_of(pprev, struct hlist_node, next);
}
}