Summary: Add kyua test for FreeBSD-SA-19:22:mbuf.

[darrick.freebsd_gmail.com]

Test Plan

Verified test passes with fix for FreeBSD-SA-19:22:mbuf and fails without it.

[cem]

Thanks! I can't speak to the test itself, as I'm not familiar with the SA.

sys/kern/uipc_mbuf2.c

505

So usually for this kind of side-effect sysctl, you would do a sysctl_handle_int() somewhere early in the function with a bogus zero output, then if (error != 0 || req->newptr == NULL) return (error);

That way simply "get"ing the value from the sysctl does not cause the side effect. (This would impact sysctl -a too, except we're using SKIP already.)

Instead, you "set" a value explicitly to run the test: sysctl debug.test_foo=1.

Test pass/failure can be indicated by returning zero (success) or an errno value, rather than in-band 0/1 SYSCTL_OUT.

Does that make sense?

509

CTLFLAG_MPSAFE, too.

tests/sys/kern/Makefile

27

This file is missing?

[darrick.freebsd_gmail.com]

sys/kern/uipc_mbuf2.c

505

Does CTLFLAG_SKIP sufficiently avoid the sysctl -a case and other inadvertent execution? I can also #ifdef INVARIANTS to make this debug only.

If the sysctl returns an errno, the 'sysctl' commandline utility still exits with a 0 exitcode and outputs nothing to stdout. For a simple atf-sh testcase I'd like either the exitcode to be non-zero for the failure case or for the output to give me the info I need. Since sysctl(1) seems to insist on returning 0 regardless of error return, it seems like I'm forced to use stdout.

[cem]

sys/kern/uipc_mbuf2.c

505

I'm on board with the proposal to rely on SKIP and INVARIANTS to prevent accidental misuse.

If the sysctl returns an errno, the 'sysctl' commandline utility still exits with a 0 exitcode and outputs nothing to stdout.

This may be true of "get" operations, but I don't believe it is true of "set" operations. We can easily prove this. (Note that 10% below is actually fairly high as there are quite a few sysctl syscalls involved in name2oiding, plus separate sysctls for IN/OUT operations; 5% may be more appropriate.)

# 5 == EIO
$ sysctl debug.fail_point.sysctl_running='10%return(5)'

# After this point, repeated trials may be necessary to overcome EIOs from name2oid or oid2fmt.  When the EIO hits the actual syscall value handler, though, the result is below:
$ sysctl kern.timecounter.alloweddeviation=5
kern.timecounter.alloweddeviation: 5
sysctl: kern.timecounter.alloweddeviation=5: Input/output error

$ echo $?
1

The syscall raised error 5; libc wrapped that in -1/errno=5; and sysctl(8) invokes warn(3) (stderr output on the 2nd line printed above) and increments warnings, which results in non-zero exit.

[darrick.freebsd_gmail.com]

Add #ifdef INVARIRANTS and NULL check.