On Tue 04-10-16 18:13:05, Oleg Nesterov wrote:

On 10/04, Michal Hocko wrote:

quoted

On Fri 30-09-16 14:47:41, Oleg Nesterov wrote:

quoted

On 09/30, Andrey Ryabinin wrote:

quoted

@@ -423,7 +424,9 @@ static int coredump_wait(int exit_code, struct core_state *core_state)
 	if (core_waiters > 0) {
 		struct core_thread *ptr;

+		freezer_do_not_count();
 		wait_for_completion(&core_state->startup);
+		freezer_count();

Agreed... we could probably even do

	--- x/fs/coredump.c
	+++ x/fs/coredump.c
	@@ -423,7 +423,13 @@ static int coredump_wait(int exit_code, 
		if (core_waiters > 0) {
			struct core_thread *ptr;
	 
	-		wait_for_completion(&core_state->startup);
	+		if (wait_for_completion_interruptible(&core_state->startup)) {
	+			/* see the comment in dump_interrupted() */
	+			down_write(&mm->mmap_sem);
	+			coredump_finish(mm, false);
	+			up_write(&mm->mmap_sem);
	+			return -EINTR;
	+		}
			/*
			 * Wait for all the threads to become inactive, so that
			 * all the thread context (extended register state, like

This looks like a very good idea to me. We really want to make the whole
coredump_wait killable.

Well, it is already killable. 

Except wait_for_completion is not killable and the exiting tasks might
be blocked in a !killable state blocking this one to continue. But...

And with the change above it can sleep
in down_write(mmap_sem) and we really need this lock to abort, so it
won't necessarily react to SIGKILL faster.

you are right that somebody might be holding mmap_sem and we cannot get
rid of it here.

quoted

I guess this should help us to remove the
hackish sig->flags & SIGNAL_GROUP_COREDUMP check from
__task_will_free_mem.

Why? This doesn't depend on "killable". __task_will_free_mem() checks
this flag to detect the CLONE_VM processes which won't exit soon because
they participate in the coredumping.

I just (wrongly) assumed that if we make this path killable completely
we can guarantee a forward progress and get rid of SIGNAL_GROUP_COREDUMP
check completely. But you are right this won't be sufficient.
-- 
Michal Hocko
SUSE Labs