Date: Thu, 9 Apr 2020 21:02:55 -0400 From: Rich Felker <dalias@...c.org> To: Florian Weimer <fw@...eb.enyo.de> Cc: musl@...ts.openwall.com, Norbert Lange <nolange79@...il.com> Subject: Re: [BUG] sysconf implementing _SC_NPROCESSORS_(CONF|ONLN) incorrectly On Thu, Apr 09, 2020 at 08:31:30PM +0200, Florian Weimer wrote: > * Szabolcs Nagy: > > > * Norbert Lange <nolange79@...il.com> [2020-04-09 12:29:20 +0200]: > >> Hello, > >> > >> I ran into a bug with trace-cmd when compiled against musl. > >> Turns out musl just returns the affinity mask in both cases. > >> > >> I know those functions are not standard, but the irony is that if they > >> are implemented, > >> then they prevent applications to use fallbacks. > >> > >> See the trace-cmd bugreport: > >> https://bugzilla.kernel.org/show_bug.cgi?id=206817 > > > > i think there are open unanswered questions about the right > > semantics it's not clear what user code may expect > > > > https://www.openwall.com/lists/musl/2019/03/16/1 > > https://www.openwall.com/lists/musl/2019/03/19/1 > > Stille, returning 1 if the sched_getaffinity system call fails > (because the affinity mask is unexpectedly large) will break some > software that assumes a true uniprocessor system if the processor > count is zero. (OpenJDK is an example.) > > This can also happen if there is some external affinity mask manager. > > For glibc, we had to change our logic to artificially inflate the CPU > to 2 if we cannot determine it, as the more conservative choice. Wait, you mean some software is abusing these interfaces to omit memory barriers or something? *facepalm* *sigh* Yes, we should probably do something better to implement these but I'm not sure what. Rich
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