On 03/14/2018 04:19 PM, Eric Blake wrote: > On 03/14/2018 10:13 AM, Eric Blake wrote: >> On 03/14/2018 10:04 AM, Tim Rühsen wrote: >>> Hi, >>> >>> >>> just stumbled upon nonintr_close() in spawn-pipe.c which has this loop: >>> >>> do >>> retval = close (fd); >>> while (retval < 0 && errno == EINTR); >>> >>> >>> Regarding the man page of libc, this shouldn't be done on certain >>> systems. E.g. it says the Linux kernel closes the file descriptor even >>> on EINTR. With the effect of possible race conditions in multi-threaded >>> code. >>> >>> >>> What do the experts here say ? >> >> Here's what POSIX has to say: >> http://austingroupbugs.net/view.php?id=529#c1200 >> >> You are correct that retrying close (fd) is a bug in multi-threaded >> programs. It is better to leak the fd (on the few implementations >> that leave fd open on EINTR failure) than to risk corrupting >> multithreaded state. If you are on a system that has posix_close() >> implemented (glibc appears to not have done it yet, and I don't know >> if any other systems have), then you are guaranteed that you can write >> race-free leak-free code. But until then, it's better to err on the >> side of safety, especially since it was only a minority of systems >> that leave fd open on EINTR failure. >> > > I didn't offer my conclusion: I think the existence of nonintr_close() > in gnulib is a bug, and should be removed. It's better to assume Linux > semantics (close ALWAYS destroys the fd, even when an error is reported) > which is safe for multithreaded apps, than to assume that EINTR leaves > the fd open (where assuming Linux semantics leaks on the few platforms > that leave the fd open, but a leak is safer than multithreaded > corruption when the wrong fd is closed on retry).
Thanks for the explanation, Eric. Sounds reasonable to me. There is also another occurrence in execute.c. With Best Regards, Tim
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