Micro optimise _callout_stop_safe() by removing dead code.

[• hselasky]

Summary

The CS_DRAIN flag cannot be set at the same time like the async-drain function
pointer is set. These are orthogonal features. Assert this at the beginning
of the function.

Before:

if (flags & CS_DRAIN) {
        /* FALLTHROUGH */
} else if (xxx) {
        return yyy;
}
if (drain) {
        zzz = drain;
}

After:

if (flags & CS_DRAIN) {
        /* FALLTHROUGH */
} else if (xxx) {
        return yyy;
} else {
        if (drain) {
                zzz = drain;
        }
}

MFC after: 1 week
Sponsored by: Mellanox Technologies // Nvidia

[• hselasky]

Improve KASSERT() message.

[markj]

sys/kern/kern_timeout.c

1278 ↗

(On Diff #76509)

I guess this KTR message was wrong before, in the case where CS_DRAIN is specified.

[markj]

sys/kern/kern_timeout.c

1280 ↗

(On Diff #76509)

What happens if a drain function for this CPU is already set by a previous call?

[• hselasky]

sys/kern/kern_timeout.c

1280 ↗

(On Diff #76509)

Setting drain is like the last thing a callout does before being freed, though we could KASSERT() that in a separate patch, that the cc_exec_drain() is NULL.

[• hselasky]

sys/kern/kern_timeout.c

1278 ↗

(On Diff #76509)

Yes, in the other case the callout is synchronously drained.