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tubik: Correct use of flags_cond and version_cond

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Waiters of flags_cond and version_cond were not doing so correctly;
the correct way is to acquire a lock prior to their respective checks,
and atomically drop/acquire that lock with pthread_cond_wait.
Otherwise, we could miss a wakeup if a flag changed between our check
and when we wait.

To make this possible, make versionLock a normal pthread mutex in
AFS_PTHREAD_ENV, so it is a lock we can pass to pthread_cond_wait.
Make the waiters pass versionLock to pthread_cond_wait, and eliminate
flags_mutex and version_mutex.

Change-Id: Id33a72182b907d069e342cb049e23868ab2f7eb9
Reviewed-on: http://gerrit.openafs.org/1681
Tested-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>
This commit is contained in:
Andrew Deason 2010-04-01 16:42:25 -05:00 committed by Derrick Brashear
parent 5a7d6da525
commit af5923c050
2 changed files with 25 additions and 16 deletions
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26
src/ubik/ubik.c
View File

@ -415,7 +415,11 @@ ubik_ServerInitCommon(afs_int32 myHost, short myPort,
tdb->activeTrans = (struct ubik_trans *)0;
memset(&tdb->version, 0, sizeof(struct ubik_version));
memset(&tdb->cachedVersion, 0, sizeof(struct ubik_version));
#ifdef AFS_PTHREAD_ENV
assert(pthread_mutex_init(&tdb->versionLock, NULL) == 0);
#else
Lock_Init(&tdb->versionLock);
#endif
tdb->flags = 0;
tdb->read = uphys_read;
tdb->write = uphys_write;
@ -434,8 +438,6 @@ ubik_ServerInitCommon(afs_int32 myHost, short myPort,
#ifdef AFS_PTHREAD_ENV
assert(pthread_cond_init(&tdb->version_cond, NULL) == 0);
assert(pthread_cond_init(&tdb->flags_cond, NULL) == 0);
assert(pthread_mutex_init(&tdb->version_mutex, NULL) == 0);
assert(pthread_mutex_init(&tdb->flags_mutex, NULL) == 0);
#endif /* AFS_PTHREAD_ENV */
/* initialize RX */
@ -662,16 +664,15 @@ BeginTrans(register struct ubik_dbase *dbase, afs_int32 transMode,
if (transMode == UBIK_WRITETRANS) {
/* if we're writing already, wait */
while (dbase->flags & DBWRITING) {
DBRELE(dbase);
#ifdef AFS_PTHREAD_ENV
assert(pthread_mutex_lock(&dbase->flags_mutex) == 0);
assert(pthread_cond_wait(&dbase->flags_cond, &dbase->flags_mutex) == 0);
assert(pthread_mutex_unlock(&dbase->flags_mutex) == 0);
assert(pthread_cond_wait(&dbase->flags_cond, &dbase->versionLock) == 0);
#else
DBRELE(dbase);
LWP_WaitProcess(&dbase->flags);
#endif
DBHOLD(dbase);
#endif
}
if (!ubeacon_AmSyncSite()) {
DBRELE(dbase);
return UNOTSYNC;
@ -1194,16 +1195,19 @@ int
ubik_WaitVersion(register struct ubik_dbase *adatabase,
register struct ubik_version *aversion)
{
DBHOLD(adatabase);
while (1) {
/* wait until version # changes, and then return */
if (vcmp(*aversion, adatabase->version) != 0)
if (vcmp(*aversion, adatabase->version) != 0) {
DBRELE(adatabase);
return 0;
}
#ifdef AFS_PTHREAD_ENV
assert(pthread_mutex_lock(&adatabase->version_mutex) == 0);
assert(pthread_cond_wait(&adatabase->version_cond,&adatabase->version_mutex) == 0);
assert(pthread_mutex_unlock(&adatabase->version_mutex) == 0);
assert(pthread_cond_wait(&adatabase->version_cond, &adatabase->versionLock) == 0);
#else
DBRELE(adatabase);
LWP_WaitProcess(&adatabase->version); /* same vers, just wait */
DBHOLD(adatabase);
#endif
}
}

15
src/ubik/ubik.p.h
View File

@ -168,7 +168,9 @@ struct ubik_dbase {
char *pathName; /*!< root name for dbase */
struct ubik_trans *activeTrans; /*!< active transaction list */
struct ubik_version version; /*!< version number */
#if defined(UKERNEL)
#ifdef AFS_PTHREAD_ENV
pthread_mutex_t versionLock; /*!< lock on version number */
#elif defined(UKERNEL)
struct afs_lock versionLock; /*!< lock on version number */
#else /* defined(UKERNEL) */
struct Lock versionLock; /*!< lock on version number */
@ -195,8 +197,6 @@ struct ubik_dbase {
#ifdef AFS_PTHREAD_ENV
pthread_cond_t version_cond; /*!< condition variable to manage changes to version */
pthread_cond_t flags_cond; /*!< condition variable to manage changes to flags */
pthread_mutex_t version_mutex;
pthread_mutex_t flags_mutex;
#endif
};
@ -291,8 +291,13 @@ struct ubik_server {
};
/*! \name hold and release functions on a database */
#define DBHOLD(a) ObtainWriteLock(&((a)->versionLock))
#define DBRELE(a) ReleaseWriteLock(&((a)->versionLock))
#ifdef AFS_PTHREAD_ENV
# define DBHOLD(a) assert(pthread_mutex_lock(&((a)->versionLock)) == 0)
# define DBRELE(a) assert(pthread_mutex_unlock(&((a)->versionLock)) == 0)
#else /* !AFS_PTHREAD_ENV */
# define DBHOLD(a) ObtainWriteLock(&((a)->versionLock))
# define DBRELE(a) ReleaseWriteLock(&((a)->versionLock))
#endif /* !AFS_PTHREAD_ENV */
/*\}*/
/* globals */