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Fix a race condition in the worker thread caching logic: if we got

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two or more syscall requests before any worker thread ran, we might
not have enough threads to handle the requests.  In some scenarios
this could lead to a deadlock.
This commit is contained in:
pooka 2011-02-06 18:25:48 +00:00
parent 28f32144bc
commit 627ff529aa
1 changed files with 9 additions and 8 deletions
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17
lib/librumpuser/rumpuser_sp.c
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@ -1,4 +1,4 @@
/* $NetBSD: rumpuser_sp.c,v 1.38 2011/01/28 19:21:28 pooka Exp $ */
/* $NetBSD: rumpuser_sp.c,v 1.39 2011/02/06 18:25:48 pooka Exp $ */
/*
* Copyright (c) 2010, 2011 Antti Kantee. All Rights Reserved.
@ -35,7 +35,7 @@
*/
#include <sys/cdefs.h>
__RCSID("$NetBSD: rumpuser_sp.c,v 1.38 2011/01/28 19:21:28 pooka Exp $");
__RCSID("$NetBSD: rumpuser_sp.c,v 1.39 2011/02/06 18:25:48 pooka Exp $");
#include <sys/types.h>
#include <sys/atomic.h>
@ -615,19 +615,18 @@ serv_syscallbouncer(void *arg)
for (;;) {
pthread_mutex_lock(&sbamtx);
if (idleworker >= rumpsp_idleworker) {
if (__predict_false(idleworker >= rumpsp_idleworker)) {
nworker--;
pthread_mutex_unlock(&sbamtx);
break;
}
idleworker++;
while (TAILQ_EMPTY(&syslist)) {
if (TAILQ_EMPTY(&syslist))
idleworker++;
while (TAILQ_EMPTY(&syslist))
pthread_cond_wait(&sbacv, &sbamtx);
}
sba = TAILQ_FIRST(&syslist);
TAILQ_REMOVE(&syslist, sba, sba_entries);
idleworker--;
pthread_mutex_unlock(&sbamtx);
serv_handlesyscall(sba->sba_spc,
@ -952,6 +951,7 @@ handlereq(struct spclient *spc)
if (idleworker > 0) {
/* do we have a daemon's tool (i.e. idle threads)? */
pthread_cond_signal(&sbacv);
idleworker--;
} else if (nworker < rumpsp_maxworker) {
/*
* Else, need to create one
@ -959,8 +959,9 @@ handlereq(struct spclient *spc)
* worker to pick up the syscall)
*/
if (pthread_create(&pt, &pattr_detached,
serv_syscallbouncer, NULL) == 0)
serv_syscallbouncer, NULL) == 0) {
nworker++;
}
}
pthread_mutex_unlock(&sbamtx);
}