* bug with sysconf(_SC_CHILD_MAX) with user process ulimit set to unlimited
@ 2017-12-07 15:26 Natanael Copa
2017-12-07 17:05 ` Rich Felker
0 siblings, 1 reply; 2+ messages in thread
From: Natanael Copa @ 2017-12-07 15:26 UTC (permalink / raw)
To: musl
Hi,
While trying to debug why `bash -c 'sleep 1 & wait $!'` hangs with
alpine in docker[1] I made an interesting discovery.
Set user process ulimit to "unlimited" and run the following program on
an x86_64 machine:
#include <stdio.h>
#include <unistd.h>
int main() {
long maxchild = sysconf(_SC_CHILD_MAX);
printf("maxchild: %ld\n", maxchild);
return 0;
}
With musl libc it prints:
maxchild: 9223372036854775807
With glibc it prints:
maxchild: -1
Setting the process ulimit to something like 64k makes bash work again.
Shouldn't sysconf(_SC_CHILD_MAX) return -1 if ulimit is set to
"unlimited"?
Thanks!
-nc
[1]: https://github.com/tianon/docker-bash/issues/4
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: bug with sysconf(_SC_CHILD_MAX) with user process ulimit set to unlimited
2017-12-07 15:26 bug with sysconf(_SC_CHILD_MAX) with user process ulimit set to unlimited Natanael Copa
@ 2017-12-07 17:05 ` Rich Felker
0 siblings, 0 replies; 2+ messages in thread
From: Rich Felker @ 2017-12-07 17:05 UTC (permalink / raw)
To: musl
On Thu, Dec 07, 2017 at 04:26:09PM +0100, Natanael Copa wrote:
> Hi,
>
> While trying to debug why `bash -c 'sleep 1 & wait $!'` hangs with
> alpine in docker[1] I made an interesting discovery.
>
> Set user process ulimit to "unlimited" and run the following program on
> an x86_64 machine:
>
> #include <stdio.h>
> #include <unistd.h>
>
> int main() {
> long maxchild = sysconf(_SC_CHILD_MAX);
> printf("maxchild: %ld\n", maxchild);
> return 0;
> }
>
>
> With musl libc it prints:
>
> maxchild: 9223372036854775807
>
> With glibc it prints:
>
> maxchild: -1
>
>
> Setting the process ulimit to something like 64k makes bash work again.
>
> Shouldn't sysconf(_SC_CHILD_MAX) return -1 if ulimit is set to
> "unlimited"?
>
> Thanks!
>
> -nc
>
>
> [1]: https://github.com/tianon/docker-bash/issues/4
Yes, I think you're completely right. But this is also a bug in bash;
its loop to "round up to a power of two" is using the wrong type and
results in an infinite loop whenever the process limit it sees is
huge:
http://git.savannah.gnu.org/cgit/bash.git/tree/jobs.c#n768
I'll make sure the patch works right and then commit your fix.
Rich
^ permalink raw reply [flat|nested] 2+ messages in thread
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2017-12-07 15:26 bug with sysconf(_SC_CHILD_MAX) with user process ulimit set to unlimited Natanael Copa
2017-12-07 17:05 ` Rich Felker
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