提交 e73f8959 编写于 作者: O Oleg Nesterov 提交者: Al Viro

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: NOleg Nesterov <oleg@redhat.com>
Acked-by: NDavid 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: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>
上级 62366c88
......@@ -1400,6 +1400,8 @@ struct task_struct {
int (*notifier)(void *priv);
void *notifier_data;
sigset_t *notifier_mask;
struct hlist_head task_works;
struct audit_context *audit_context;
#ifdef CONFIG_AUDITSYSCALL
uid_t loginuid;
......
#ifndef _LINUX_TASK_WORK_H
#define _LINUX_TASK_WORK_H
#include <linux/list.h>
#include <linux/sched.h>
struct task_work;
typedef void (*task_work_func_t)(struct task_work *);
struct task_work {
struct hlist_node hlist;
task_work_func_t func;
void *data;
};
static inline void
init_task_work(struct task_work *twork, task_work_func_t func, void *data)
{
twork->func = func;
twork->data = data;
}
int task_work_add(struct task_struct *task, struct task_work *twork, bool);
struct task_work *task_work_cancel(struct task_struct *, task_work_func_t);
void task_work_run(void);
static inline void exit_task_work(struct task_struct *task)
{
if (unlikely(!hlist_empty(&task->task_works)))
task_work_run();
}
#endif /* _LINUX_TASK_WORK_H */
......@@ -49,6 +49,7 @@
#include <linux/sched.h>
#include <linux/ptrace.h>
#include <linux/security.h>
#include <linux/task_work.h>
struct linux_binprm;
/*
......@@ -164,8 +165,10 @@ static inline void tracehook_signal_handler(int sig, siginfo_t *info,
*/
static inline void set_notify_resume(struct task_struct *task)
{
#ifdef TIF_NOTIFY_RESUME
if (!test_and_set_tsk_thread_flag(task, TIF_NOTIFY_RESUME))
kick_process(task);
#endif
}
/**
......@@ -185,6 +188,14 @@ static inline void tracehook_notify_resume(struct pt_regs *regs)
{
if (current->replacement_session_keyring)
key_replace_session_keyring();
/*
* The caller just cleared TIF_NOTIFY_RESUME. This barrier
* pairs with task_work_add()->set_notify_resume() after
* hlist_add_head(task->task_works);
*/
smp_mb__after_clear_bit();
if (unlikely(!hlist_empty(&current->task_works)))
task_work_run();
}
#endif /* <linux/tracehook.h> */
......@@ -5,7 +5,7 @@
obj-y = fork.o exec_domain.o panic.o printk.o \
cpu.o exit.o itimer.o time.o softirq.o resource.o \
sysctl.o sysctl_binary.o capability.o ptrace.o timer.o user.o \
signal.o sys.o kmod.o workqueue.o pid.o \
signal.o sys.o kmod.o workqueue.o pid.o task_work.o \
rcupdate.o extable.o params.o posix-timers.o \
kthread.o wait.o kfifo.o sys_ni.o posix-cpu-timers.o mutex.o \
hrtimer.o rwsem.o nsproxy.o srcu.o semaphore.o \
......
......@@ -946,11 +946,14 @@ void do_exit(long code)
exit_signals(tsk); /* sets PF_EXITING */
/*
* tsk->flags are checked in the futex code to protect against
* an exiting task cleaning up the robust pi futexes.
* an exiting task cleaning up the robust pi futexes, and in
* task_work_add() to avoid the race with exit_task_work().
*/
smp_mb();
raw_spin_unlock_wait(&tsk->pi_lock);
exit_task_work(tsk);
exit_irq_thread();
if (unlikely(in_atomic()))
......
......@@ -1411,6 +1411,7 @@ static struct task_struct *copy_process(unsigned long clone_flags,
*/
p->group_leader = p;
INIT_LIST_HEAD(&p->thread_group);
INIT_HLIST_HEAD(&p->task_works);
/* Now that the task is set up, run cgroup callbacks if
* necessary. We need to run them before the task is visible
......
#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);
}
}
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