CVS commit: src/sys/kern

["Robert Elz" <kre%netbsd.org@localhost>]

Module Name:    src
Committed By:   kre
Date:           Sun Mar 10 13:44:49 UTC 2019

Modified Files:
        src/sys/kern: kern_timeout.c

Log Message:
Undo previous, in the name of "defined" behaviour, it breaks things.

This is all explained in the comment at the head of the file:

 * Some of the "math" in here is a bit tricky.  We have to beware of
 * wrapping ints.
 *
 * [...] but c->c_time can
 * be positive or negative so comparing it with anything is dangerous.

In particular, "if (c->c_time > ticks)" is simply wrong.

 * The only way we can use the c->c_time value in any predictable way is
 * when we calculate how far in the future `to' will timeout - "c->c_time
 * - c->c_cpu->cc_ticks".  The result will always be positive for future
 * timeouts and 0 or negative for due timeouts.

Go back to the old way.   But write the calculation of delta slightly
differently which will hopefully appease KUBsan.   Perhaps.  In any
case, this code works on any system that NetBSD has any hope of ever
running on, whatever the C standards say is "defined" behaviour.


To generate a diff of this commit:
cvs rdiff -u -r1.55 -r1.56 src/sys/kern/kern_timeout.c

Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.