Olivier Langlois <olivier@xxxxxxxxxxxxxx> writes: > On Wed, 2021-06-09 at 16:05 -0500, Eric W. Biederman wrote: >> > >> > So the TIF_NOTIFY_SIGNAL does get set WHILE the core dump is >> > written. >> >> Did you mean? >> >> So the TIF_NOTIFY_SIGNAL does _not_ get set WHILE the core dump is >> written. >> >> > Absolutely not. I did really mean what I have said. Bear with me that, > I am not qualifying myself as an expert kernel dev yet so feel free to > correct me if I say some heresy... No. I was just asking to make certain I understood what you said. I thought you said you were getting a consistent 0 byte coredump, and that implied that TIF_NOTIFY_SIGNAL was coming in before the coredump even started. > io_uring is placing my task in my TCP socket wait queue because it > wants to read data from it. > > The task returns to user space and core dump with a SEGV. > > now my understanding is that the code that is waking up tasks, it is > the NIC driver interrupt handler which can occur while the core dump is > written. > > does that make sense? > > my testing is telling me that this is exactly what happens... If you are getting partial coredumps that completely makes sense. I was hoping that by this time Jens or Oleg would have been able to chime in and at least confirm I am not missing something subtle. I was afraid for a little bit that the file system code in called in dump_emit would be checking signal_pending. After looking into that I see that the filesystem code very reasonably limits itself to testing fatal_signal_pending (because by definition disk I/O on unix is not interruptible). So I will spin up a good version of my patch (based on your patch) so we can unbreak coredumps. Eric
