On 04/02/2014 05:22 PM, Vince Weaver wrote: > On Wed, 2 Apr 2014, Michael Kerrisk (man-pages) wrote: > >> I applied, and reworked the text to be: >> >> PERF_FLAG_FD_CLOEXEC (since Linux 3.14). >> This flag enables the close-on-exec flag for the created >> event file descriptor, so that the file descriptor is >> automatically closed on execve(2). Setting the close- >> on-exec flags at creation time, rather than later with >> fcntl(2), avoids potential race conditions where the >> calling thread invokes perf_event_open() at the same >> time as another thread calls fork(2) then execve(2). >> >> Okay? > > I think the actual race condition being worried about is this: > > > thread1 thread2 > > fd=perf_event_open() | > | fork() > | exec() > | | > fcntl(CLOEXEC) | > fd has escaped past exec because > fcntl didn't happen fast enough Yes, that's the one. > so if you do a > > fd=perf_event_open(...,PERF_FLAG_FD_CLOEXEC); > > then fd is always CLOEXEC and you don't have a brief window of time > before the fcntl() where the fd can escape. > > > I'm not sure of a scuccint way to express that though. I think the existing text suffices. Cheers, Michael -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/ -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
