Al Viro <viro@xxxxxxxxxxxxxxxxxx> writes:
On Mon, Jun 21, 2021 at 01:54:56PM +0000, Al Viro wrote:
On Tue, Jun 15, 2021 at 02:58:12PM -0700, Linus Torvalds wrote:
And I think our horrible "kernel threads return to user space when
done" is absolutely horrifically nasty. Maybe of the clever sort, but
mostly of the historical horror sort.
How would you prefer to handle that, then? Separate magical path from
kernel_execve() to switch to userland? We used to have something of
that sort, and that had been a real horror...
As it is, it's "kernel thread is spawned at the point similar to
ret_from_fork(), runs the payload (which almost never returns) and
then proceeds out to userland, same way fork(2) would've done."
That way kernel_execve() doesn't have to do anything magical.
Al, digging through the old notes and current call graph...
FWIW, the major assumption back then had been that get_signal(),
signal_delivered() and all associated machinery (including coredumps)
runs *only* from SIGPENDING/NOTIFY_SIGNAL handling.
And "has complete registers on stack" is only a part of that;
there was other fun stuff in the area ;-/ Do we want coredumps for
those, and if we do, will the de_thread stuff work there?
Do we want coredumps from processes that use io_uring? yes
Exactly what we want from io_uring threads is less clear. We can't
really give much that is meaningful beyond the thread ids of the
io_uring threads.
What problems do are you seeing beyond the missing registers on the
stack for kernel threads?
I don't immediately see the connection between coredumps and de_thread.
The function de_thread arranges for the fatal_signal_pending to be true,
and that should work just fine for io_uring threads. The io_uring
threads process the fatal_signal with get_signal and then proceed to
exit eventually calling do_exit.
Eric
