sysctl_kern_proc_umask: fast path when operating on curproc

[kaktus]

Summary

Make sysctl_kern_proc_umask execute fast path when requested pid in curproc->p_pid or 0, avoiding unnecessary locking. Update libc consumer to skip calling getpid().

Sponsored by: Mysterious Code Ltd.

Test Plan

rebuild and reinstall kernel and libc, run program using KERN_PROC_UMASK oid, ie. procstat -s pid, observe UMASK field.

[robak]

Mind adding testing instructions?

[mjg]

For consistency this should also remove SLOCK/SUNLOCK in the lookup case, otherwise LGTM.

[robak]

In D12972#269385, @mjg wrote:

For consistency this should also remove SLOCK/SUNLOCK in the lookup case, otherwise LGTM.

In such case I'm stopping the tests (large poudriere builds) until fixed version is submitted.

[kaktus]

Address @mjg comments and remove extra FILEDESC locks.

[robak]

The updated version seems to survive large Poudriere builds and works as described in test instructions. Waiting for @mjg or @kib to approve it before committing.

[robak]

Committed in r325516.

[cem]

sys/kern/kern_proc.c

2781–2783

What is the justification for removing this locking? Mjg comment above says "for consistency," but I'm not sure with what. Thanks!

[kaktus]

sys/kern/kern_proc.c

2781–2783

To consistency with the new fast path and other places in kernel that read fd_cmask without acquiring the lock. fd_cmask is declared as short, hence in small enough to guarantee atomic read.

[cem]

sys/kern/kern_proc.c

2781–2783

Thanks!