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Code Issues Releases Wiki Activity

Lock view while accessing its zone table

Browse Source 
Commit 308bc46a59 introduced a change to
the view_flushanddetach() function which makes the latter access
view->zonetable without holding view->lock.  As confirmed by TSAN, this
enables races between threads for view->zonetable accesses.

Swap the view->zonetable pointer under view lock and then detach the
local swapped dns_zt_t later when the view lock is already unlocked.

This commit also changes the dns_zt interfaces, so the setting the
zonetable "flush" flag is separate operation to dns_zt_detach,
e.g. instead of doing:

    if (view->flush) {
        dns_zt_flushanddetach(&zt);
    } else {
        dns_zt_detach(&zt);
    }

the code is now:

    if (view->flush) {
        dns_zt_flush(zt);
    }
    dns_zt_detach(&zt);

making the code more consistent with how we handle flushing and
detaching dns_zone_t pointers from the view.
This commit is contained in:
Ondřej Surý
2022-01-03 21:37:46 +01:00
parent 7624dc3ee4
commit f326d45135
3 changed files with 24 additions and 24 deletions
Download Patch File Download Diff File Expand all files Collapse all files

9
lib/dns/include/dns/zt.h
View File

@@ -117,14 +117,13 @@ dns_zt_detach(dns_zt_t **ztp);
*/
void
dns_zt_flushanddetach(dns_zt_t **ztp);
dns_zt_flush(dns_zt_t *ztp);
/*%<
* Detach the given zonetable, if the reference count goes to zero the
* zonetable will be flushed and then freed. In either case 'ztp' is
* set to NULL.
* Schedule flushing of the given zonetable, when reference count goes
* to zero.
*
* Requires:
* \li '*ztp' to be valid
* \li 'ztp' to be valid
*/
void

20
lib/dns/view.c
View File

@@ -632,6 +632,7 @@ view_flushanddetach(dns_view_t **viewp, bool flush) {
if (isc_refcount_decrement(&view->references) == 1) {
dns_zone_t *mkzone = NULL, *rdzone = NULL;
dns_zt_t *zt = NULL;
isc_refcount_destroy(&view->references);
@@ -645,13 +646,16 @@ view_flushanddetach(dns_view_t **viewp, bool flush) {
dns_requestmgr_shutdown(view->requestmgr);
}
if (view->zonetable != NULL && view->flush) {
dns_zt_flushanddetach(&view->zonetable);
} else if (view->zonetable != NULL) {
dns_zt_detach(&view->zonetable);
LOCK(&view->lock);
if (view->zonetable != NULL) {
zt = view->zonetable;
view->zonetable = NULL;
if (view->flush) {
dns_zt_flush(zt);
}
}
LOCK(&view->lock);
if (view->managed_keys != NULL) {
mkzone = view->managed_keys;
view->managed_keys = NULL;
@@ -674,7 +678,11 @@ view_flushanddetach(dns_view_t **viewp, bool flush) {
}
UNLOCK(&view->lock);
/* Need to detach zones outside view lock */
/* Need to detach zt and zones outside view lock */
if (zt != NULL) {
dns_zt_detach(&zt);
}
if (mkzone != NULL) {
dns_zone_detach(&mkzone);
}

19
lib/dns/zt.c
View File

@@ -225,14 +225,15 @@ zt_destroy(dns_zt_t *zt) {
if (atomic_load_acquire(&zt->flush)) {
(void)dns_zt_apply(zt, false, NULL, flush, NULL);
}
dns_rbt_destroy(&zt->table);
isc_rwlock_destroy(&zt->rwlock);
zt->magic = 0;
isc_mem_putanddetach(&zt->mctx, zt, sizeof(*zt));
}
static void
zt_flushanddetach(dns_zt_t **ztp, bool need_flush) {
void
dns_zt_detach(dns_zt_t **ztp) {
dns_zt_t *zt;
REQUIRE(ztp != NULL && VALID_ZT(*ztp));
@@ -240,23 +241,15 @@ zt_flushanddetach(dns_zt_t **ztp, bool need_flush) {
zt = *ztp;
*ztp = NULL;
if (need_flush) {
atomic_store_release(&zt->flush, true);
}
if (isc_refcount_decrement(&zt->references) == 1) {
zt_destroy(zt);
}
}
void
dns_zt_flushanddetach(dns_zt_t **ztp) {
zt_flushanddetach(ztp, true);
}
void
dns_zt_detach(dns_zt_t **ztp) {
zt_flushanddetach(ztp, false);
dns_zt_flush(dns_zt_t *zt) {
REQUIRE(VALID_ZT(zt));
atomic_store_release(&zt->flush, true);
}
isc_result_t