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[PATCH] taskstats: don't use tasklist_lock

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Remove tasklist_lock from taskstats.c. find_task_by_pid() is rcu-safe.
->siglock allows us to traverse subthread without tasklist.

Q: delay accounting looks wrong to me.  If sub-thread has already called
taskstats_exit_send() but didn't call release_task(self) yet it will be
accounted twice.  The window is big.  No?

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Shailabh Nagar <nagar@watson.ibm.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Jay Lan <jlan@sgi.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Oleg Nesterov 2006-10-28 10:38:54 -07:00 committed by Linus Torvalds
parent b8534d7bd8
commit a98b609426
1 changed files with 24 additions and 35 deletions
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59
kernel/taskstats.c
View file

@ -174,21 +174,19 @@ static void send_cpu_listeners(struct sk_buff *skb, unsigned int cpu)
up_write(&listeners->sem);
}
static int fill_pid(pid_t pid, struct task_struct *pidtsk,
static int fill_pid(pid_t pid, struct task_struct *tsk,
struct taskstats *stats)
{
int rc = 0;
struct task_struct *tsk = pidtsk;
if (!pidtsk) {
read_lock(&tasklist_lock);
if (!tsk) {
rcu_read_lock();
tsk = find_task_by_pid(pid);
if (!tsk) {
read_unlock(&tasklist_lock);
if (tsk)
get_task_struct(tsk);
rcu_read_unlock();
if (!tsk)
return -ESRCH;
}
get_task_struct(tsk);
read_unlock(&tasklist_lock);
} else
get_task_struct(tsk);
@ -214,40 +212,28 @@ static int fill_pid(pid_t pid, struct task_struct *pidtsk,
}
static int fill_tgid(pid_t tgid, struct task_struct *tgidtsk,
static int fill_tgid(pid_t tgid, struct task_struct *first,
struct taskstats *stats)
{
struct task_struct *tsk, *first;
struct task_struct *tsk;
unsigned long flags;
int rc = -ESRCH;
/*
* Add additional stats from live tasks except zombie thread group
* leaders who are already counted with the dead tasks
*/
first = tgidtsk;
if (!first) {
read_lock(&tasklist_lock);
rcu_read_lock();
if (!first)
first = find_task_by_pid(tgid);
if (!first) {
read_unlock(&tasklist_lock);
return -ESRCH;
}
get_task_struct(first);
read_unlock(&tasklist_lock);
} else
get_task_struct(first);
if (!first || !lock_task_sighand(first, &flags))
goto out;
if (first->signal->stats)
memcpy(stats, first->signal->stats, sizeof(*stats));
tsk = first;
read_lock(&tasklist_lock);
/* Start with stats from dead tasks */
if (first->sighand) {
spin_lock_irqsave(&first->sighand->siglock, flags);
if (first->signal->stats)
memcpy(stats, first->signal->stats, sizeof(*stats));
spin_unlock_irqrestore(&first->sighand->siglock, flags);
}
do {
if (tsk->exit_state == EXIT_ZOMBIE && thread_group_leader(tsk))
continue;
@ -260,15 +246,18 @@ static int fill_tgid(pid_t tgid, struct task_struct *tgidtsk,
delayacct_add_tsk(stats, tsk);
} while_each_thread(first, tsk);
read_unlock(&tasklist_lock);
stats->version = TASKSTATS_VERSION;
unlock_task_sighand(first, &flags);
rc = 0;
out:
rcu_read_unlock();
stats->version = TASKSTATS_VERSION;
/*
* Accounting subsytems can also add calls here to modify
* fields of taskstats.
*/
put_task_struct(first);
return 0;
return rc;
}