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Fix reference counting in get_attached_entry (again)

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When get_attached_entry() encounters entry that would be expired, it
needs to get reference to the entry before calling maybe_expire_entry(),
so the ADB entry doesn't get destroyed inside the its own lock.

This creeped into the code base again during review, so I am adding
an extra comment to prevent this.
This commit is contained in:
Ondřej Surý 2022-12-16 21:46:50 +01:00
parent 096b047628
commit 32ff134eeb
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GPG Key ID: 2820F37E873DEA41
1 changed files with 8 additions and 3 deletions
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11
lib/dns/adb.c
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@ -1368,12 +1368,14 @@ get_attached_and_locked_name(dns_adb_t *adb, const dns_name_t *name,
adbname);
INSIST(result == ISC_R_SUCCESS);
dns_adbname_ref(adbname);
LOCK(&adbname->lock); /* Must be unlocked by the caller */
adbname->last_used = now;
ISC_LIST_PREPEND(adb->names_lru, adbname, link);
break;
case ISC_R_SUCCESS:
dns_adbname_ref(adbname);
LOCK(&adbname->lock); /* Must be unlocked by the caller */
if (adbname->last_used + ADB_CACHE_MINIMUM <= last_update) {
adbname->last_used = now;
@ -1386,7 +1388,6 @@ get_attached_and_locked_name(dns_adb_t *adb, const dns_name_t *name,
UNREACHABLE();
}
dns_adbname_ref(adbname);
/*
* The refcount is now 2 and the final detach will happen in
* expire_name() - the unused adbname stored in the hashtable and lru
@ -1436,6 +1437,7 @@ get_attached_and_locked_entry(dns_adb_t *adb, isc_stdtime_t now,
sizeof(adbentry->sockaddr), adbentry);
INSIST(result == ISC_R_SUCCESS);
dns_adbentry_ref(adbentry);
LOCK(&adbentry->lock); /* Must be unlocked by the caller */
adbentry->last_used = now;
@ -1443,6 +1445,11 @@ get_attached_and_locked_entry(dns_adb_t *adb, isc_stdtime_t now,
break;
}
case ISC_R_SUCCESS:
/*
* The dns_adbentry_ref() must stay here before trying to expire
* the ADB entry, so it is not destroyed under the lock.
*/
dns_adbentry_ref(adbentry);
LOCK(&adbentry->lock); /* Must be unlocked by the caller */
if (maybe_expire_entry(adbentry, now)) {
UNLOCK(&adbentry->lock);
@ -1460,8 +1467,6 @@ get_attached_and_locked_entry(dns_adb_t *adb, isc_stdtime_t now,
UNREACHABLE();
}
dns_adbentry_ref(adbentry);
UNLOCK(&adb->entries_lock);
return (adbentry);