From d30fda355188272430d3865db2ff9e24b4135ae3 Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Wed, 26 May 2010 14:43:13 -0700 Subject: [PATCH] posix-cpu-timers: avoid "task->signal != NULL" checks Preparation to make task->signal immutable, no functional changes. posix-cpu-timers.c checks task->signal != NULL to ensure this task is alive and didn't pass __exit_signal(). This is correct but we are going to change the lifetime rules for ->signal and never reset this pointer. Change the code to check ->sighand instead, it doesn't matter which pointer we check under tasklist, they both are cleared simultaneously. As Roland pointed out, some of these changes are not strictly needed and probably it makes sense to revert them later, when ->signal will be pinned to task_struct. But this patch tries to ensure the subsequent changes in fork/exit can't make any visible impact on posix cpu timers. Signed-off-by: Oleg Nesterov Cc: Fenghua Yu Acked-by: Roland McGrath Cc: Stanislaw Gruszka Cc: Tony Luck Cc: Thomas Gleixner Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/posix-cpu-timers.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c index 00bb252f29a2..9829646d399c 100644 --- a/kernel/posix-cpu-timers.c +++ b/kernel/posix-cpu-timers.c @@ -363,7 +363,7 @@ int posix_cpu_clock_get(const clockid_t which_clock, struct timespec *tp) } } else { read_lock(&tasklist_lock); - if (thread_group_leader(p) && p->signal) { + if (thread_group_leader(p) && p->sighand) { error = cpu_clock_sample_group(which_clock, p, &rtn); @@ -439,7 +439,7 @@ int posix_cpu_timer_del(struct k_itimer *timer) if (likely(p != NULL)) { read_lock(&tasklist_lock); - if (unlikely(p->signal == NULL)) { + if (unlikely(p->sighand == NULL)) { /* * We raced with the reaping of the task. * The deletion should have cleared us off the list. @@ -691,10 +691,10 @@ int posix_cpu_timer_set(struct k_itimer *timer, int flags, read_lock(&tasklist_lock); /* * We need the tasklist_lock to protect against reaping that - * clears p->signal. If p has just been reaped, we can no + * clears p->sighand. If p has just been reaped, we can no * longer get any information about it at all. */ - if (unlikely(p->signal == NULL)) { + if (unlikely(p->sighand == NULL)) { read_unlock(&tasklist_lock); put_task_struct(p); timer->it.cpu.task = NULL; @@ -863,7 +863,7 @@ void posix_cpu_timer_get(struct k_itimer *timer, struct itimerspec *itp) clear_dead = p->exit_state; } else { read_lock(&tasklist_lock); - if (unlikely(p->signal == NULL)) { + if (unlikely(p->sighand == NULL)) { /* * The process has been reaped. * We can't even collect a sample any more. @@ -1199,7 +1199,7 @@ void posix_cpu_timer_schedule(struct k_itimer *timer) spin_lock(&p->sighand->siglock); } else { read_lock(&tasklist_lock); - if (unlikely(p->signal == NULL)) { + if (unlikely(p->sighand == NULL)) { /* * The process has been reaped. * We can't even collect a sample any more. -- 2.20.1