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[PATCH] posix-timers: fix cleanup_timers() and run_posix_cpu_timers() races 

1. cleanup_timers() sets timer->task = NULL under tasklist + ->sighand locks.
   That means that this code in posix_cpu_timer_del() and posix_cpu_timer_set()

   		lock_timer(timer);
		if (timer->task == NULL)
			return;
		read_lock(tasklist);
		put_task_struct(timer->task)

   is racy. With this patch timer->task modified and accounted only under
   timer->it_lock. Sadly, this means that dead task_struct won't be freed
   until timer deleted or armed.

2. run_posix_cpu_timers() collects expired timers into local list under
   tasklist + ->sighand again. That means that posix_cpu_timer_del()
   should check timer->it.cpu.firing under these locks too.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Oleg Nesterov 2005-10-23 20:25:39 +04:00 committed by Linus Torvalds
parent ba9e358fd0
commit 108150ea78
1 changed files with 11 additions and 20 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

29
kernel/posix-cpu-timers.c
View File

@ -380,14 +380,9 @@ int posix_cpu_timer_create(struct k_itimer *new_timer)
int posix_cpu_timer_del(struct k_itimer *timer)
{
struct task_struct *p = timer->it.cpu.task;
int ret = 0;
if (timer->it.cpu.firing)
return TIMER_RETRY;
if (unlikely(p == NULL))
return 0;
if (!list_empty(&timer->it.cpu.entry)) {
if (likely(p != NULL)) {
read_lock(&tasklist_lock);
if (unlikely(p->signal == NULL)) {
/*
@ -396,18 +391,20 @@ int posix_cpu_timer_del(struct k_itimer *timer)
*/
BUG_ON(!list_empty(&timer->it.cpu.entry));
} else {
/*
* Take us off the task's timer list.
*/
spin_lock(&p->sighand->siglock);
if (timer->it.cpu.firing)
ret = TIMER_RETRY;
else
list_del(&timer->it.cpu.entry);
spin_unlock(&p->sighand->siglock);
}
read_unlock(&tasklist_lock);
}
put_task_struct(p);
return 0;
if (!ret)
put_task_struct(p);
}
return ret;
}
/*
@ -424,8 +421,6 @@ static void cleanup_timers(struct list_head *head,
cputime_t ptime = cputime_add(utime, stime);
list_for_each_entry_safe(timer, next, head, entry) {
put_task_struct(timer->task);
timer->task = NULL;
list_del_init(&timer->entry);
if (cputime_lt(timer->expires.cpu, ptime)) {
timer->expires.cpu = cputime_zero;
@ -437,8 +432,6 @@ static void cleanup_timers(struct list_head *head,
++head;
list_for_each_entry_safe(timer, next, head, entry) {
put_task_struct(timer->task);
timer->task = NULL;
list_del_init(&timer->entry);
if (cputime_lt(timer->expires.cpu, utime)) {
timer->expires.cpu = cputime_zero;
@ -450,8 +443,6 @@ static void cleanup_timers(struct list_head *head,
++head;
list_for_each_entry_safe(timer, next, head, entry) {
put_task_struct(timer->task);
timer->task = NULL;
list_del_init(&timer->entry);
if (timer->expires.sched < sched_time) {
timer->expires.sched = 0;