Re: [RFC] coredump: Do not interrupt dump for TIF_NOTIFY_SIGNAL

Linus Torvalds [off-list ref] writes:

On Wed, Jun 9, 2021 at 1:17 PM Eric W. Biederman [off-list ref] wrote:

quoted

quoted

In short the coredump code deliberately supports being interrupted by
SIGKILL, and depends upon prepare_signal to filter out all other
signals.

Hmm.

I have to say, that looks like the core reason for the bug: if you
want to be interrupted by a fatal signal, you shouldn't use
signal_pending(), you should use fatal_signal_pending().

Now, the fact that we haven't cleared TIF_NOTIFY_SIGNAL for the first
signal is clearly the immediate cause of this, but at the same time I
really get the feeling that that coredump aborting code should always
had used fatal_signal_pending().

We do want to be able to abort core-dumps (stuck network filesystems
is the traditional reason), but the fact that it used signal_pending()
looks buggy.

In fact, the very comment in that dump_interrupted() function seems to
acknowledge that signal_pending() is all kinds of silly.

So regardless of the fact that io_uring does seem to have messed up
this part of signals, I think the fix is not to change
signal_pending() to task_sigpending(), but to just do what the comment
suggests we should do.

It looks like it would need to be:

static bool dump_interrupted(void)
{
	return fatal_signal_pending() || freezing();
}

As the original implementation of dump_interrupted 528f827ee0bb
("coredump: introduce dump_interrupted()") is deliberately allowing the
freezer to terminate the core dumps to allow for reliable system
suspend.

But also:

quoted

With the io_uring code comes an extra test in signal_pending
for TIF_NOTIFY_SIGNAL (which is something about asking a task to run
task_work_run).

Jens, is this still relevant? Maybe we can revert that whole series
now, and make the confusing difference between signal_pending() and
task_sigpending() go away again?

               Linus