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authorOleg Nesterov <oleg@redhat.com>2010-11-05 16:53:42 +0100
committerLinus Torvalds <torvalds@linux-foundation.org>2010-11-05 14:16:03 -0700
commite0a70217107e6f9844628120412cb27bb4cea194 (patch)
tree3c805ee6cfe97afee77b226e0cf5d36135e82dda
parentb312e131cb88b83b6edc7a017b0249b4ea176edc (diff)
posix-cpu-timers: workaround to suppress the problems with mt exec
posix-cpu-timers.c correctly assumes that the dying process does posix_cpu_timers_exit_group() and removes all !CPUCLOCK_PERTHREAD timers from signal->cpu_timers list. But, it also assumes that timer->it.cpu.task is always the group leader, and thus the dead ->task means the dead thread group. This is obviously not true after de_thread() changes the leader. After that almost every posix_cpu_timer_ method has problems. It is not simple to fix this bug correctly. First of all, I think that timer->it.cpu should use struct pid instead of task_struct. Also, the locking should be reworked completely. In particular, tasklist_lock should not be used at all. This all needs a lot of nontrivial and hard-to-test changes. Change __exit_signal() to do posix_cpu_timers_exit_group() when the old leader dies during exec. This is not the fix, just the temporary hack to hide the problem for 2.6.37 and stable. IOW, this is obviously wrong but this is what we currently have anyway: cpu timers do not work after mt exec. In theory this change adds another race. The exiting leader can detach the timers which were attached to the new leader. However, the window between de_thread() and release_task() is small, we can pretend that sys_timer_create() was called before de_thread(). Signed-off-by: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--kernel/exit.c8
1 files changed, 8 insertions, 0 deletions
diff --git a/kernel/exit.c b/kernel/exit.c
index b194febf5799..21aa7b3001fb 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -96,6 +96,14 @@ static void __exit_signal(struct task_struct *tsk)
sig->tty = NULL;
} else {
/*
+ * This can only happen if the caller is de_thread().
+ * FIXME: this is the temporary hack, we should teach
+ * posix-cpu-timers to handle this case correctly.
+ */
+ if (unlikely(has_group_leader_pid(tsk)))
+ posix_cpu_timers_exit_group(tsk);
+
+ /*
* If there is any task waiting for the group exit
* then notify it:
*/

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