Hello Keno On 12/03/2017 04:15 AM, Keno Fischer wrote: > Resending as plain text (apologies for those receiving it twice, and > those that got > an HTML copy, I'm used to my mail client switching that over > automatically, which > for some reason didn't happen here). > > > This is exactly the discussion I want to generate, so thank you. > I should point out that I'm not advocating for anything other > than clarity of what kernel behavior user space may assume. So, should the documentation patch be applied at this point, or dropped? Thanks, Michael > On Sat, Dec 2, 2017 at 9:25 PM, Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote: >> On Sat, Dec 02, 2017 at 07:23:59PM -0500, Keno Fischer wrote: >>> The catalyst for this patch was me experiencing EINTR errors when >>> using the 9p file system. In linux commit 9523feac, the 9p file >>> system was changed to use wait_event_killable instead of >>> wait_event_interruptible, which does indeed address my problem, >>> but also makes me a bit unhappy, because uninterruptable waits >>> prevents things like ^C'ing the execution and some debugging >>> tools which depend on being able to cancel long-running operations >>> by sending signals. >> >> Wait, wait, wait. killable is not uninterruptible. It's "can accept >> a signal if the signal is fatal". ie userspace will never see it. >> So, no, it doesn't prevent ^C. It does prevent the debugging tool you're >> talking about from working, because it's handling the signal, so it's not >> fatal. > > This probably shows that I've been in REPL based environments too long, > that catch SIGINT ;). You are of course correct that a fatal SIGINT would > still be delivered. > >>> I realize I'm probably 20 years too late here, but it feels like >>> clarificaion on what to expect from the kernel would still go a long >>> way here. >> >> A change to user-visible behaviour has to be opt-in. > > I agree. However, it was my impression that stat() can return EINTR > depending on the file system. Prior to the referenced commit, > this was certainly true on 9p and I suspect it's not the only network file > system for which this is true (though prior to my experiencing this > with 9p, the only > time I've ever experienced it was on HPC clusters with who knows what > code providing the network filesystem). If it is indeed the case that > an EINTR return from stat() and similar is illegal and should be considered > a kernel bug, a statement to that extent all I'm looking for here. > -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/
