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posix-timers: use "struct pid*" instead of "struct task_struct*" 

Impact: restructure, clean up code

k_itimer holds the ref to the ->it_process until sys_timer_delete(). This
allows to pin up to RLIMIT_SIGPENDING dead task_struct's. Change the code
to use "struct pid *" instead.

The patch doesn't kill ->it_process, it places ->it_pid into the union.
->it_process is still used by do_cpu_nanosleep() as before. It would be
trivial to change the nanosleep code as well, but since it uses it_process
in a special way I think it is better to keep this field for grep.

The patch bloats the kernel by 104 bytes and it also adds the new pointer,
->it_signal, to k_itimer. It is used by lock_timer() to verify that the
found timer was not created by another process. It is not clear why do we
use the global database (and thus the global idr_lock) for posix timers.
We still need the signal_struct->posix_timers which contains all useable
timers, perhaps it is better to use some form of per-process array
instead.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Oleg Nesterov 2008-12-01 14:18:13 -08:00 committed by Ingo Molnar
parent 6c34bc2976
commit 27af4245b6
2 changed files with 28 additions and 21 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
include/linux/posix-timers.h
View File

@ -45,7 +45,11 @@ struct k_itimer {
int it_requeue_pending; /* waiting to requeue this timer */
#define REQUEUE_PENDING 1
int it_sigev_notify; /* notify word of sigevent struct */
struct task_struct *it_process; /* process to send signal to */
struct signal_struct *it_signal;
union {
struct pid *it_pid; /* pid of process to send signal to */
struct task_struct *it_process; /* for clock_nanosleep */
};
struct sigqueue *sigq; /* signal queue entry. */
union {
struct {

43
kernel/posix-timers.c
View File

@ -116,7 +116,7 @@ static DEFINE_SPINLOCK(idr_lock);
* must supply functions here, even if the function just returns
* ENOSYS. The standard POSIX timer management code assumes the
* following: 1.) The k_itimer struct (sched.h) is used for the
* timer. 2.) The list, it_lock, it_clock, it_id and it_process
* timer. 2.) The list, it_lock, it_clock, it_id and it_pid
* fields are not modified by timer code.
*
* At this time all functions EXCEPT clock_nanosleep can be
@ -313,7 +313,8 @@ void do_schedule_next_timer(struct siginfo *info)
int posix_timer_event(struct k_itimer *timr, int si_private)
{
int shared, ret;
struct task_struct *task;
int shared, ret = -1;
/*
* FIXME: if ->sigq is queued we can race with
* dequeue_signal()->do_schedule_next_timer().
@ -327,8 +328,13 @@ int posix_timer_event(struct k_itimer *timr, int si_private)
*/
timr->sigq->info.si_sys_private = si_private;
shared = !(timr->it_sigev_notify & SIGEV_THREAD_ID);
ret = send_sigqueue(timr->sigq, timr->it_process, shared);
rcu_read_lock();
task = pid_task(timr->it_pid, PIDTYPE_PID);
if (task) {
shared = !(timr->it_sigev_notify & SIGEV_THREAD_ID);
ret = send_sigqueue(timr->sigq, task, shared);
}
rcu_read_unlock();
/* If we failed to send the signal the timer stops. */
return ret > 0;
}
@ -405,7 +411,7 @@ static enum hrtimer_restart posix_timer_fn(struct hrtimer *timer)
return ret;
}
static struct task_struct * good_sigevent(sigevent_t * event)
static struct pid *good_sigevent(sigevent_t * event)
{
struct task_struct *rtn = current->group_leader;
@ -419,7 +425,7 @@ static struct task_struct * good_sigevent(sigevent_t * event)
((event->sigev_signo <= 0) || (event->sigev_signo > SIGRTMAX)))
return NULL;
return rtn;
return task_pid(rtn);
}
void register_posix_clock(const clockid_t clock_id, struct k_clock *new_clock)
@ -471,7 +477,7 @@ sys_timer_create(const clockid_t which_clock,
{
struct k_itimer *new_timer;
int error, new_timer_id;
struct task_struct *process;
struct pid *it_pid;
sigevent_t event;
int it_id_set = IT_ID_NOT_SET;
@ -525,11 +531,9 @@ sys_timer_create(const clockid_t which_clock,
goto out;
}
rcu_read_lock();
process = good_sigevent(&event);
if (process)
get_task_struct(process);
it_pid = get_pid(good_sigevent(&event));
rcu_read_unlock();
if (!process) {
if (!it_pid) {
error = -EINVAL;
goto out;
}
@ -537,8 +541,7 @@ sys_timer_create(const clockid_t which_clock,
event.sigev_notify = SIGEV_SIGNAL;
event.sigev_signo = SIGALRM;
event.sigev_value.sival_int = new_timer->it_id;
process = current->group_leader;
get_task_struct(process);
it_pid = get_pid(task_tgid(current));
}
new_timer->it_sigev_notify = event.sigev_notify;
@ -548,7 +551,8 @@ sys_timer_create(const clockid_t which_clock,
new_timer->sigq->info.si_code = SI_TIMER;
spin_lock_irq(&current->sighand->siglock);
new_timer->it_process = process;
new_timer->it_pid = it_pid;
new_timer->it_signal = current->signal;
list_add(&new_timer->list, &current->signal->posix_timers);
spin_unlock_irq(&current->sighand->siglock);
@ -583,8 +587,7 @@ static struct k_itimer *lock_timer(timer_t timer_id, unsigned long *flags)
timr = idr_find(&posix_timers_id, (int)timer_id);
if (timr) {
spin_lock(&timr->it_lock);
if (timr->it_process &&
same_thread_group(timr->it_process, current)) {
if (timr->it_pid && timr->it_signal == current->signal) {
spin_unlock(&idr_lock);
return timr;
}
@ -831,8 +834,8 @@ retry_delete:
* This keeps any tasks waiting on the spin lock from thinking
* they got something (see the lock code above).
*/
put_task_struct(timer->it_process);
timer->it_process = NULL;
put_pid(timer->it_pid);
timer->it_pid = NULL;
unlock_timer(timer, flags);
release_posix_timer(timer, IT_ID_SET);
@ -858,8 +861,8 @@ retry_delete:
* This keeps any tasks waiting on the spin lock from thinking
* they got something (see the lock code above).
*/
put_task_struct(timer->it_process);
timer->it_process = NULL;
put_pid(timer->it_pid);
timer->it_pid = NULL;
unlock_timer(timer, flags);
release_posix_timer(timer, IT_ID_SET);