Revert "Fix cpu timers exit deadlock and races"

Revert commit e03d13e985d48ac4885382c9e3b1510c78bd047f, to be replaced
by a much nicer fix from Roland.

1 files changed, 17 insertions, 11 deletions

diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c
index b3f3edc475d..7a51a5597c3 100644
--- a/kernel/posix-cpu-timers.c
+++ b/kernel/posix-cpu-timers.c
@@ -387,19 +387,25 @@ int posix_cpu_timer_del(struct k_itimer *timer)
         if (unlikely(p == NULL))
                 return 0;
 
-        spin_lock(&p->sighand->siglock);
         if (!list_empty(&timer->it.cpu.entry)) {
-                /*
-                 * Take us off the task's timer list.  We don't need to
-                 * take tasklist_lock and check for the task being reaped.
-                 * If it was reaped, it already called posix_cpu_timers_exit
-                 * and posix_cpu_timers_exit_group to clear all the timers
-                 * that pointed to it.
-                 */
-                list_del(&timer->it.cpu.entry);
-                put_task_struct(p);
+                read_lock(&tasklist_lock);
+                if (unlikely(p->signal == NULL)) {
+                        /*
+                         * We raced with the reaping of the task.
+                         * The deletion should have cleared us off the list.
+                         */
+                        BUG_ON(!list_empty(&timer->it.cpu.entry));
+                } else {
+                        /*
+                         * Take us off the task's timer list.
+                         */
+                        spin_lock(&p->sighand->siglock);
+                        list_del(&timer->it.cpu.entry);
+                        spin_unlock(&p->sighand->siglock);
+                }
+                read_unlock(&tasklist_lock);
         }
-        spin_unlock(&p->sighand->siglock);
+        put_task_struct(p);
 
         return 0;
 }