Date: Sat, 16 Mar 2002 20:39:03 +0900 From: Seigo Tanimura <tanimura@r.dl.itc.u-tokyo.ac.jp> To: Alfred Perlstein <bright@mu.org> Cc: "Brian F. Feldman" <green@FreeBSD.org>, jhb@FreeBSD.org, current@FreeBSD.org, Seigo Tanimura <tanimura@r.dl.itc.u-tokyo.ac.jp> Subject: Re: sx_upgrade() (was: Re: cvs commit: src/sys/kern kern_mtxpool.c src/sys/sys kernel.h src/sys/vm vm_fault.c vm_glue.c vm_map.c vm_map.h vm_pageout.c vm_zone.c) Message-ID: <200203161140.g2GBd3A5015244@silver.carrots.uucp.r.dl.itc.u-tokyo.ac.jp> In-Reply-To: <200203161009.g2GA8rA5092735@silver.carrots.uucp.r.dl.itc.u-tokyo.ac.jp> References: <20020315054113.GC4857@elvis.mu.org> <200203151121.g2FBLnj36094@green.bikeshed.org> <20020315185320.GJ4857@elvis.mu.org> <200203161009.g2GA8rA5092735@silver.carrots.uucp.r.dl.itc.u-tokyo.ac.jp>
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On Sat, 16 Mar 2002 19:08:53 +0900,
Seigo Tanimura <tanimura@r.dl.itc.u-tokyo.ac.jp> said:
Seigo> Attached patch implements sx_upgrade() which should work as you said
Seigo> above. This compiles fine, but is not tested yet.
The last patch breaks INVARIANTS. This one compiles and seems to work.
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==== //depot/user/tanimura/inodezone_uma/kern/kern_sx.c#1 - /home/nkth/tanimura/p4-freefall/inodezone_uma/kern/kern_sx.c ====
--- /tmp/tmp.515.0 Sat Mar 16 20:31:14 2002
+++ /home/nkth/tanimura/p4-freefall/inodezone_uma/kern/kern_sx.c Sat Mar 16 19:37:13 2002
@@ -42,6 +42,7 @@
#include <sys/lock.h>
#include <sys/mutex.h>
#include <sys/sx.h>
+#include <sys/proc.h>
struct lock_class lock_class_sx = {
"sx",
@@ -72,6 +73,7 @@
cv_init(&sx->sx_excl_cv, description);
sx->sx_excl_wcnt = 0;
sx->sx_xholder = NULL;
+ sx->sx_upgrader = NULL;
LOCK_LOG_INIT(lock, 0);
@@ -215,7 +217,15 @@
* there are exclusive lock waiters.
*/
if (sx->sx_excl_wcnt > 0) {
- if (sx->sx_cnt == 0)
+ /*
+ * The upgrader beats any other exclusive lockers.
+ * Note that the upgrader holds the last shared lock.
+ */
+ if (sx->sx_upgrader != NULL && sx->sx_cnt == 1) {
+ KASSERT((sx->sx_upgrader->td_flags & TDF_CVWAITQ) != 0,
+ ("_sx_sunlock: the upgrader is not waiting for sx_excl_cv"));
+ cv_waitq_remove(sx->sx_upgrader);
+ } else if (sx->sx_cnt == 0)
cv_signal(&sx->sx_excl_cv);
} else if (sx->sx_shrd_wcnt > 0)
cv_broadcast(&sx->sx_shrd_cv);
@@ -250,6 +260,45 @@
LOCK_LOG_LOCK("XUNLOCK", &sx->sx_object, 0, 0, file, line);
mtx_unlock(sx->sx_lock);
+}
+
+int
+_sx_upgrade(struct sx *sx, const char *file, int line)
+{
+
+ _sx_assert(sx, SX_SLOCKED, file, line);
+ mtx_lock(sx->sx_lock);
+
+ /*
+ * If another thread is waiting for lock upgrade,
+ * the curtherad must unlock this sx.
+ */
+ if (sx->sx_upgrader != NULL) {
+ mtx_unlock(sx->sx_lock);
+ return (0);
+ }
+ sx->sx_upgrader = curthread;
+
+ /* Loop in case we lose the race for lock acquisition. */
+ while (sx->sx_cnt != 1) {
+ sx->sx_excl_wcnt++;
+ cv_wait(&sx->sx_excl_cv, sx->sx_lock);
+ sx->sx_excl_wcnt--;
+ }
+
+ /* We must be the sole thread slocking this sx. */
+ MPASS(sx->sx_cnt == 1);
+
+ /* Acquire an exclusive lock. */
+ sx->sx_cnt = -1;
+ sx->sx_xholder = curthread;
+ sx->sx_upgrader = NULL;
+
+ LOCK_LOG_LOCK("XUPGRADE", &sx->sx_object, 0, 1, file, line);
+ WITNESS_UPGRADE(&sx->sx_object, LOP_EXCLUSIVE, file, line);
+
+ mtx_unlock(sx->sx_lock);
+ return (1);
}
int
==== //depot/user/tanimura/inodezone_uma/kern/subr_witness.c#1 - /home/nkth/tanimura/p4-freefall/inodezone_uma/kern/subr_witness.c ====
--- /tmp/tmp.515.1 Sat Mar 16 20:31:16 2002
+++ /home/nkth/tanimura/p4-freefall/inodezone_uma/kern/subr_witness.c Sat Mar 16 19:18:12 2002
@@ -717,9 +717,9 @@
if ((lock->lo_flags & LO_UPGRADABLE) == 0)
panic("upgrade of non-upgradable lock (%s) %s @ %s:%d",
class->lc_name, lock->lo_name, file, line);
- if ((flags & LOP_TRYLOCK) == 0)
- panic("non-try upgrade of lock (%s) %s @ %s:%d", class->lc_name,
- lock->lo_name, file, line);
+ if ((flags & LOP_TRYLOCK) == 0) {
+ /* TODO: check for lock order reversal. */
+ }
if ((lock->lo_class->lc_flags & LC_SLEEPLOCK) == 0)
panic("upgrade of non-sleep lock (%s) %s @ %s:%d",
class->lc_name, lock->lo_name, file, line);
==== //depot/user/tanimura/inodezone_uma/sys/sx.h#1 - /home/nkth/tanimura/p4-freefall/inodezone_uma/sys/sx.h ====
--- /tmp/tmp.515.2 Sat Mar 16 20:31:17 2002
+++ /home/nkth/tanimura/p4-freefall/inodezone_uma/sys/sx.h Sat Mar 16 19:18:12 2002
@@ -44,6 +44,7 @@
struct cv sx_excl_cv; /* xlock waiters. */
int sx_excl_wcnt; /* Number of xlock waiters. */
struct thread *sx_xholder; /* Thread presently holding xlock. */
+ struct thread *sx_upgrader; /* Thread presently waiting for lock upgrade. */
};
#ifdef _KERNEL
@@ -55,6 +56,7 @@
int _sx_try_xlock(struct sx *sx, const char *file, int line);
void _sx_sunlock(struct sx *sx, const char *file, int line);
void _sx_xunlock(struct sx *sx, const char *file, int line);
+int _sx_upgrade(struct sx *sx, const char *file, int line);
int _sx_try_upgrade(struct sx *sx, const char *file, int line);
void _sx_downgrade(struct sx *sx, const char *file, int line);
#ifdef INVARIANT_SUPPORT
@@ -67,6 +69,7 @@
#define sx_try_xlock(sx) _sx_try_xlock((sx), LOCK_FILE, LOCK_LINE)
#define sx_sunlock(sx) _sx_sunlock((sx), LOCK_FILE, LOCK_LINE)
#define sx_xunlock(sx) _sx_xunlock((sx), LOCK_FILE, LOCK_LINE)
+#define sx_upgrade(sx) _sx_upgrade((sx), LOCK_FILE, LOCK_LINE)
#define sx_try_upgrade(sx) _sx_try_upgrade((sx), LOCK_FILE, LOCK_LINE)
#define sx_downgrade(sx) _sx_downgrade((sx), LOCK_FILE, LOCK_LINE)
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--
Seigo Tanimura <tanimura@r.dl.itc.u-tokyo.ac.jp> <tanimura@FreeBSD.org>
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