Messages in this thread Patch in this message | | | Date | Wed, 3 Nov 2010 12:58:32 +0200 | From | Sergey Senozhatsky <> | Subject | Re: [PATCH] posix-cpu-timers: rcu_read_lock/unlock protect find_task_by_vpid call |
| |
On (11/02/10 19:33), Oleg Nesterov wrote: > > On Tue, 2 Nov 2010, Sergey Senozhatsky wrote: > > > > > > We can remove the tasklist_lock while at it. rcu_read_lock is enough. > > > > > > Yes, I believe posix-cpu-timers.c shouldn't use tasklist at all, > but it is not trivial to change this code. > >[..] > > I think this change is fine, but please note that thread_group_leader() > check is not relaible without tasklist. If we race with de_thread() > find_task_by_vpid() can find the new leader before it updates its > ->group_leader. IOW, posix_cpu_timer_create() can fail when it shouldn't. > > Not that I think this really matters, posix_cpu_timer_create() has > other problems with de_thread(). But perhaps it makes sense to > change posix_cpu_timer_create() to use has_group_leader_pid() instead, > just to make this code not look racy and avoid adding new problems. > > The real fix, I think, should change cpu_timer_list to use > struct pid* instead of task_struct. >
Hello, Using has_group_leader_pid instead of thread_group_leader, when tasklist_lock is not aquired (check_clock and posix_cpu_timer_create).
---
diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c index 6842eeb..05bb717 100644 --- a/kernel/posix-cpu-timers.c +++ b/kernel/posix-cpu-timers.c @@ -37,13 +37,13 @@ static int check_clock(const clockid_t which_clock) if (pid == 0) return 0; - read_lock(&tasklist_lock); + rcu_read_lock(); p = find_task_by_vpid(pid); if (!p || !(CPUCLOCK_PERTHREAD(which_clock) ? - same_thread_group(p, current) : thread_group_leader(p))) { + same_thread_group(p, current) : has_group_leader_pid(p))) { error = -EINVAL; } - read_unlock(&tasklist_lock); + rcu_read_unlock(); return error; } @@ -390,7 +390,7 @@ int posix_cpu_timer_create(struct k_itimer *new_timer) INIT_LIST_HEAD(&new_timer->it.cpu.entry); - read_lock(&tasklist_lock); + rcu_read_lock(); if (CPUCLOCK_PERTHREAD(new_timer->it_clock)) { if (pid == 0) { p = current; @@ -404,7 +404,7 @@ int posix_cpu_timer_create(struct k_itimer *new_timer) p = current->group_leader; } else { p = find_task_by_vpid(pid); - if (p && !thread_group_leader(p)) + if (p && !has_group_leader_pid(p)) p = NULL; } } @@ -414,7 +414,7 @@ int posix_cpu_timer_create(struct k_itimer *new_timer) } else { ret = -EINVAL; } - read_unlock(&tasklist_lock); + rcu_read_unlock(); return ret; }
[unhandled content-type:application/pgp-signature] | |