Module Name: src
Committed By: riastradh
Date: Sun May 3 01:19:47 UTC 2020
Modified Files:
src/sys/kern: kern_condvar.c
Log Message:
Fix edge cases in cv_timedwaitbt, cv_timedwaitbt_sig.
- If the timeout is exactly zero, fail immediately with EWOULDBLOCK.
- If the timeout is just so small it would be rounded to zero ticks,
make sure to wait at least one tick.
- Make sure we never return with a negative timeout left.
To generate a diff of this commit:
cvs rdiff -u -r1.47 -r1.48 src/sys/kern/kern_condvar.c
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/sys/kern/kern_condvar.c
diff -u src/sys/kern/kern_condvar.c:1.47 src/sys/kern/kern_condvar.c:1.48
--- src/sys/kern/kern_condvar.c:1.47 Sun Apr 19 20:35:29 2020
+++ src/sys/kern/kern_condvar.c Sun May 3 01:19:47 2020
@@ -1,4 +1,4 @@
-/* $NetBSD: kern_condvar.c,v 1.47 2020/04/19 20:35:29 ad Exp $ */
+/* $NetBSD: kern_condvar.c,v 1.48 2020/05/03 01:19:47 riastradh Exp $ */
/*-
* Copyright (c) 2006, 2007, 2008, 2019, 2020 The NetBSD Foundation, Inc.
@@ -34,7 +34,7 @@
*/
#include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: kern_condvar.c,v 1.47 2020/04/19 20:35:29 ad Exp $");
+__KERNEL_RCSID(0, "$NetBSD: kern_condvar.c,v 1.48 2020/05/03 01:19:47 riastradh Exp $");
#include <sys/param.h>
#include <sys/systm.h>
@@ -334,23 +334,45 @@ cv_timedwaitbt(kcondvar_t *cv, kmutex_t
{
struct bintime slept;
unsigned start, end;
+ int timo;
int error;
KASSERTMSG(bt->sec >= 0, "negative timeout");
KASSERTMSG(epsilon != NULL, "specify maximum requested delay");
+ /* If there's nothing left to wait, time out. */
+ if (bt->sec == 0 && bt->frac == 0)
+ return EWOULDBLOCK;
+
+ /* Convert to ticks, but clamp to be >=1. */
+ timo = bintime2timo(bt);
+ KASSERTMSG(timo >= 0, "negative ticks: %d", timo);
+ if (timo == 0)
+ timo = 1;
+
/*
* getticks() is technically int, but nothing special
* happens instead of overflow, so we assume two's-complement
* wraparound and just treat it as unsigned.
*/
start = getticks();
- error = cv_timedwait(cv, mtx, bintime2timo(bt));
+ error = cv_timedwait(cv, mtx, timo);
end = getticks();
+ /*
+ * Set it to the time left, or zero, whichever is larger. We
+ * do not fail with EWOULDBLOCK here because this may have been
+ * an explicit wakeup, so the caller needs to check before they
+ * give up or else cv_signal would be lost.
+ */
slept = timo2bintime(end - start);
- /* bt := bt - slept */
- bintime_sub(bt, &slept);
+ if (bintimecmp(bt, &slept, <=)) {
+ bt->sec = 0;
+ bt->frac = 0;
+ } else {
+ /* bt := bt - slept */
+ bintime_sub(bt, &slept);
+ }
return error;
}
@@ -377,23 +399,45 @@ cv_timedwaitbt_sig(kcondvar_t *cv, kmute
{
struct bintime slept;
unsigned start, end;
+ int timo;
int error;
KASSERTMSG(bt->sec >= 0, "negative timeout");
KASSERTMSG(epsilon != NULL, "specify maximum requested delay");
+ /* If there's nothing left to wait, time out. */
+ if (bt->sec == 0 && bt->frac == 0)
+ return EWOULDBLOCK;
+
+ /* Convert to ticks, but clamp to be >=1. */
+ timo = bintime2timo(bt);
+ KASSERTMSG(timo >= 0, "negative ticks: %d", timo);
+ if (timo == 0)
+ timo = 1;
+
/*
* getticks() is technically int, but nothing special
* happens instead of overflow, so we assume two's-complement
* wraparound and just treat it as unsigned.
*/
start = getticks();
- error = cv_timedwait_sig(cv, mtx, bintime2timo(bt));
+ error = cv_timedwait_sig(cv, mtx, timo);
end = getticks();
+ /*
+ * Set it to the time left, or zero, whichever is larger. We
+ * do not fail with EWOULDBLOCK here because this may have been
+ * an explicit wakeup, so the caller needs to check before they
+ * give up or else cv_signal would be lost.
+ */
slept = timo2bintime(end - start);
- /* bt := bt - slept */
- bintime_sub(bt, &slept);
+ if (bintimecmp(bt, &slept, <=)) {
+ bt->sec = 0;
+ bt->frac = 0;
+ } else {
+ /* bt := bt - slept */
+ bintime_sub(bt, &slept);
+ }
return error;
}
