* Re: musl nice() posix compliance issue [not found] <CAKTZs+oqBk6M8JihSTPQphrLTL18EOnjvp+Atwd6a5NMLn0o=Q@mail.gmail.com> @ 2018-04-15 18:58 ` Rich Felker 2018-04-16 21:35 ` Rich Felker 0 siblings, 1 reply; 2+ messages in thread From: Rich Felker @ 2018-04-15 18:58 UTC (permalink / raw) To: Justine Tunney; +Cc: musl On Sun, Apr 15, 2018 at 10:17:37AM -0700, Justine Tunney wrote: > According to Python 2.7 autoconf, musl's nice() function needs to do this. > I checked latest release and HEAD. > > C library/kernel differences > POSIX.1 specifies that nice() should return the new nice value. > However, the raw Linux system call returns 0 on success. Likewise, the > nice() wrapper function provided in glibc 2.2.3 and > earlier returns 0 on success. This analysis seems correct, and from what I can tell, the SYS_nice syscall simply isn't usable to implement nice() because it doesn't provide the resulting nice level. So I think we have to fully drop use of it. OTOH SYS_get/setpriority are also problematic because of non-atomicity; we can and probably should try to patch that up by blocking signals and taking a lock around the operation -- but I'm not sure Linux even correctly applies the priority to all threads rather than just the calling thread, anyway... Do you know? Rich ^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: Re: musl nice() posix compliance issue 2018-04-15 18:58 ` musl nice() posix compliance issue Rich Felker @ 2018-04-16 21:35 ` Rich Felker 0 siblings, 0 replies; 2+ messages in thread From: Rich Felker @ 2018-04-16 21:35 UTC (permalink / raw) To: Justine Tunney; +Cc: musl On Sun, Apr 15, 2018 at 02:58:16PM -0400, Rich Felker wrote: > On Sun, Apr 15, 2018 at 10:17:37AM -0700, Justine Tunney wrote: > > According to Python 2.7 autoconf, musl's nice() function needs to do this. > > I checked latest release and HEAD. > > > > C library/kernel differences > > POSIX.1 specifies that nice() should return the new nice value. > > However, the raw Linux system call returns 0 on success. Likewise, the > > nice() wrapper function provided in glibc 2.2.3 and > > earlier returns 0 on success. > > This analysis seems correct, and from what I can tell, the SYS_nice > syscall simply isn't usable to implement nice() because it doesn't > provide the resulting nice level. So I think we have to fully drop use > of it. OTOH SYS_get/setpriority are also problematic because of > non-atomicity; we can and probably should try to patch that up by > blocking signals and taking a lock around the operation -- but I'm not > sure Linux even correctly applies the priority to all threads rather > than just the calling thread, anyway... Do you know? It doesn't, but this is a separate bug that can be worked around on its own. I'll apply a fix for the part you reported first. Rich ^ permalink raw reply [flat|nested] 2+ messages in thread
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2018-04-15 18:58 ` musl nice() posix compliance issue Rich Felker
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