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From: tip-bot for Oleg Nesterov on 18 Jun 2010 06:30
Commit-ID: 0bdd2ed4138ec04e09b4f8165981efc99e439f55
Gitweb: http://git.kernel.org/tip/0bdd2ed4138ec04e09b4f8165981efc99e439f55
Author: Oleg Nesterov <oleg(a)redhat.com>
AuthorDate: Fri, 11 Jun 2010 01:10:18 +0200
Committer: Ingo Molnar <mingo(a)elte.hu>
CommitDate: Fri, 18 Jun 2010 10:46:57 +0200

sched: run_posix_cpu_timers: Don't check ->exit_state, use lock_task_sighand()

run_posix_cpu_timers() doesn't work if current has already passed
exit_notify(). This was needed to prevent the races with do_wait().

Since ea6d290c ->signal is always valid and can't go away. We can
remove the "tsk->exit_state == 0" in fastpath_timer_check() and
convert run_posix_cpu_timers() to use lock_task_sighand().

Note: it makes sense to take group_leader's sighand instead, the
sub-thread still uses CPU after release_task(). But we need more
changes to do this.

Signed-off-by: Oleg Nesterov <oleg(a)redhat.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra(a)chello.nl>
LKML-Reference: <20100610231018.GA25942(a)redhat.com>
Signed-off-by: Ingo Molnar <mingo(a)elte.hu>
---
kernel/posix-cpu-timers.c | 10 ++++------
1 files changed, 4 insertions(+), 6 deletions(-)

diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c
index bf2a650..d5dbef5 100644
--- a/kernel/posix-cpu-timers.c
+++ b/kernel/posix-cpu-timers.c
@@ -1272,10 +1272,6 @@ static inline int fastpath_timer_check(struct task_struct *tsk)
{
struct signal_struct *sig;

- /* tsk == current, ensure it is safe to use ->signal/sighand */
- if (unlikely(tsk->exit_state))
- return 0;
-
if (!task_cputime_zero(&tsk->cputime_expires)) {
struct task_cputime task_sample = {
.utime = tsk->utime,
@@ -1308,6 +1304,7 @@ void run_posix_cpu_timers(struct task_struct *tsk)
{
LIST_HEAD(firing);
struct k_itimer *timer, *next;
+ unsigned long flags;

BUG_ON(!irqs_disabled());

@@ -1318,7 +1315,8 @@ void run_posix_cpu_timers(struct task_struct *tsk)
if (!fastpath_timer_check(tsk))
return;

- spin_lock(&tsk->sighand->siglock);
+ if (!lock_task_sighand(tsk, &flags))
+ return;
/*
* Here we take off tsk->signal->cpu_timers[N] and
* tsk->cpu_timers[N] all the timers that are firing, and
@@ -1340,7 +1338,7 @@ void run_posix_cpu_timers(struct task_struct *tsk)
* that gets the timer lock before we do will give it up and
* spin until we've taken care of that timer below.
*/
- spin_unlock(&tsk->sighand->siglock);
+ unlock_task_sighand(tsk, &flags);

/*
* Now that all the timers on our list have the firing flag,
--
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Prev: [tip:sched/core] sched: thread_group_cputime: Simplify, document the "alive" check
Next: ASoC: Fix overflow bug in SOC_DOUBLE_R_SX_TLV