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 <oleg@redhat.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Acked-by: Roland McGrath <roland@redhat.com>
Cc: Stanislaw Gruszka <sgruszka@redhat.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c
index 00bb252..9829646 100644
--- a/kernel/posix-cpu-timers.c
+++ b/kernel/posix-cpu-timers.c
@@ -363,7 +363,7 @@
}
} 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 @@
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 @@
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 @@
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 @@
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.