Aren/NetBSD
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

comments and assertions.

Browse Source 
no functional changes.
This commit is contained in:
yamt 2012-06-15 13:51:40 +00:00
parent 403de81b16
commit f562b34504
1 changed files with 34 additions and 14 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

48
sys/kern/kern_turnstile.c
View File

@ -1,4 +1,4 @@
/* $NetBSD: kern_turnstile.c,v 1.31 2011/12/02 12:31:53 yamt Exp $ */
/* $NetBSD: kern_turnstile.c,v 1.32 2012/06/15 13:51:40 yamt Exp $ */
/*-
* Copyright (c) 2002, 2006, 2007, 2009 The NetBSD Foundation, Inc.
@ -60,7 +60,7 @@
*/
#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: kern_turnstile.c,v 1.31 2011/12/02 12:31:53 yamt Exp $");
__KERNEL_RCSID(0, "$NetBSD: kern_turnstile.c,v 1.32 2012/06/15 13:51:40 yamt Exp $");
#include <sys/param.h>
#include <sys/lockdebug.h>
@ -199,7 +199,9 @@ turnstile_exit(wchan_t obj)
*
* Lend our priority to lwps on the blocking chain.
*
*
* If the current owner of the lock (l->l_wchan, set by sleepq_enqueue)
* has a priority lower than ours (lwp_eprio(l)), lend our priority to
* him to avoid priority inversions.
*/
static void
@ -225,29 +227,37 @@ turnstile_lendpri(lwp_t *cur)
if (l->l_wchan == NULL)
break;
/*
* Ask syncobj the owner of the lock.
*/
owner = (*l->l_syncobj->sobj_owner)(l->l_wchan);
if (owner == NULL)
break;
/* The owner may have changed as we have dropped the tc lock */
/*
* The owner may have changed as we have dropped the tc lock.
*/
if (cur == owner) {
/*
* we own the lock: stop here, sleepq_block()
* should wake up immediatly
* We own the lock: stop here, sleepq_block()
* should wake up immediatly.
*/
break;
}
if (l->l_mutex != owner->l_mutex)
dolock = true;
else
dolock = false;
/*
* Acquire owner->l_mutex if we don't have it yet.
* Because we already have another LWP lock (l->l_mutex) held,
* we need to play a try lock dance to avoid deadlock.
*/
dolock = l->l_mutex != owner->l_mutex;
if (l == owner || (dolock && !lwp_trylock(owner))) {
/*
* restart from curlwp.
* The owner was changed behind us or trylock failed.
* Restart from curlwp.
*
* Note that there may be a livelock here:
* the owner may try grabing cur's lock (which is
* the tc lock) while we're trying to grab
* the owner's lock.
* the owner may try grabing cur's lock (which is the
* tc lock) while we're trying to grab the owner's lock.
*/
lwp_unlock(l);
l = cur;
@ -255,11 +265,20 @@ turnstile_lendpri(lwp_t *cur)
prio = lwp_eprio(l);
continue;
}
/*
* If the owner's priority is already higher than ours,
* there's nothing to do anymore.
*/
if (prio <= lwp_eprio(owner)) {
if (dolock)
lwp_unlock(owner);
break;
}
/*
* Lend our priority to the 'owner' LWP.
*
* Update lenders info for turnstile_unlendpri.
*/
ts = l->l_ts;
KASSERT(ts->ts_inheritor == owner || ts->ts_inheritor == NULL);
if (ts->ts_inheritor == NULL) {
@ -273,6 +292,7 @@ turnstile_lendpri(lwp_t *cur)
}
if (dolock)
lwp_unlock(l);
LOCKDEBUG_BARRIER(owner->l_mutex, 1);
l = owner;
}
LOCKDEBUG_BARRIER(l->l_mutex, 1);