On Thu, Jun 19, 2008 at 06:38:24AM -0400, Jeff Layton wrote: > On Thu, 19 Jun 2008 12:29:16 +1000 > Neil Brown <neilb@xxxxxxx> wrote: > > > On Wednesday June 18, jlayton@xxxxxxxxxx wrote: > > > > > > No objection to the patch, but what signal was being sent to nfsd when > > > you saw this? If it's anything but a SIGKILL, then I wonder if we have > > > a race that we need to deal with. My understanding is that we have nfsd > > > flip between 2 sigmasks to prevent anything but a SIGKILL from being > > > delivered while we're handling the local filesystem operation. > > > > SuSE /etc/init.d/nfsserver does > > > > killproc -n -KILL nfsd > > > > so it looks like a SIGKILL. > > > > > > > > > > From nfsd(): > > > > > > ----------[snip]----------- > > > sigprocmask(SIG_SETMASK, &shutdown_mask, NULL); > > > > > > /* > > > * Find a socket with data available and call its > > > * recvfrom routine. > > > */ > > > while ((err = svc_recv(rqstp, 60*60*HZ)) == -EAGAIN) > > > ; > > > if (err < 0) > > > break; > > > update_thread_usage(atomic_read(&nfsd_busy)); > > > atomic_inc(&nfsd_busy); > > > > > > /* Lock the export hash tables for reading. */ > > > exp_readlock(); > > > > > > /* Process request with signals blocked. */ > > > sigprocmask(SIG_SETMASK, &allowed_mask, NULL); > > > > > > svc_process(rqstp); > > > > > > ----------[snip]----------- > > > > > > What happens if this catches a SIGINT after the err<0 check, but before > > > the mask is set to allowed_mask? Does svc_process() then get called with > > > a signal pending? > > > > Yes, I suspect it does. > > > > I wonder why we have all this mucking about this signal masks anyway. > > Anyone have any ideas about what it actually achieves? > > > > HCH asked me the same question when I did the conversion to kthreads. > My interpretation (based on guesswork here) was that we wanted to > distinguish between SIGKILL and other allowed signals. A SIGKILL is > allowed to interrupt the underlying I/O, but other signals should not. > > The question to answer here, I suppose, is whether masking a pending > signal is sufficient to make signal_pending() return false. If I'm > looking correctly then the answer should be "yes". Just looking out of curiosity: signal_pending() checks whether some thread_info->flags has TIF_SIGPENDING set. sigprocmask() sets current->blocked to the given set, then calls recalc_sigpending(), which (ignoring some freezer and SIGSTOP code that I don't understand), clears TIF_SIGPENDING if any pending signals are in the newly blocked set. So, yes. --b. > So I don't think we > have a race here after all. I suspect that if SuSE used a different > signal here, that would prevent this from happening. For the record, > both RHEL and Fedora's init scripts use SIGINT for this. -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
