| Message ID | 20110829140509.GC18871@mtj.dyndns.org (mailing list archive) |
|---|---|
| State | Not Applicable, archived |
| Headers | show |
On 08/29, Tejun Heo wrote: > > There's no try_to_freeze() call in the exit path and the only > necessary guarantee is that freezer doesn't hang waiting for zombies. > Set PF_NOFREEZE right before setting tsk->state to TASK_DEAD instead. Agreed. But I'd like to repeat, this looks "asymmetrical". do_each_thread() can't see the (auto)reaped tasks after they do exit_notify(). So we can only see this PF_NOFREEZE if the thread becomes a zombie. > @@ -1044,6 +1038,10 @@ NORET_TYPE void do_exit(long code) > > preempt_disable(); > exit_rcu(); > + > + /* this task is now dead and freezer should ignore it */ > + current->flags |= PF_NOFREEZE; > + > /* causes final put_task_struct in finish_task_switch(). */ > tsk->state = TASK_DEAD; May be freezing_slow_path() can check TASK_DEAD along with PF_NOFREEZE instead? (or tsk->exit_state != 0 to avoid the asymmetry above). Just to keep this logic in the freezer code. I dunno. But this all is up to you and Rafael, I am not arguing. Just random thoughts. Oleg.
Index: work/kernel/exit.c =================================================================== --- work.orig/kernel/exit.c +++ work/kernel/exit.c @@ -913,12 +913,6 @@ NORET_TYPE void do_exit(long code) ptrace_event(PTRACE_EVENT_EXIT, code); - /* - * With ptrace notification done, there's no point in freezing from - * here on. Disallow freezing. - */ - current->flags |= PF_NOFREEZE; - validate_creds_for_do_exit(tsk); /* @@ -1044,6 +1038,10 @@ NORET_TYPE void do_exit(long code) preempt_disable(); exit_rcu(); + + /* this task is now dead and freezer should ignore it */ + current->flags |= PF_NOFREEZE; + /* causes final put_task_struct in finish_task_switch(). */ tsk->state = TASK_DEAD; schedule();
3fb45733df "freezer: make exiting tasks properly unfreezable" removed clear_freeze_flag() from exit path and set PF_NOFREEZE right after PTRACE_EVENT_EXIT; however, Oleg pointed out that following exit paths may cause interaction with device drivers after PM freezer consider the system frozen. There's no try_to_freeze() call in the exit path and the only necessary guarantee is that freezer doesn't hang waiting for zombies. Set PF_NOFREEZE right before setting tsk->state to TASK_DEAD instead. Signed-off-by: Tejun Heo <tj@kernel.org> Reported-by: Oleg Nesterov <oleg@redhat.com> Cc: "Rafael J. Wysocki" <rjw@sisk.pl> --- kernel/exit.c | 10 ++++------ 1 file changed, 4 insertions(+), 6 deletions(-)