diff options
Diffstat (limited to 'content')
| -rw-r--r-- | content/llcache.c | 37 |
1 files changed, 34 insertions, 3 deletions
diff --git a/content/llcache.c b/content/llcache.c index f775c0f52..484954be3 100644 --- a/content/llcache.c +++ b/content/llcache.c @@ -1311,10 +1311,36 @@ nserror llcache_object_notify_users(llcache_object *object) llcache_handle *handle = &user->handle; const llcache_fetch_state objstate = object->fetch.state; - /* Save identity of next user in case client destroys - * the user underneath us */ + /* Flag that this user is the current iteration target + * in case the client attempts to destroy it underneath us */ user->iterator_target = true; - next_user = user->next; + + /* A note on the computation of next_user: + * + * Within this loop, we may make a number of calls to + * client code. Our contract with clients is that they + * can do whatever they like from within their callback + * handlers. This is so that we limit the pain of + * reentrancy to this module alone. + * + * One of the things a client can do from within its + * callback handler is to remove users from this object's + * user list. In the common case, the user they attempt + * to remove is the current iteration target, and we + * already protect against that causing problems here. + * However, no such protection exists if the client + * attempts to remove other users from this object's + * user list. + * + * Therefore, we cannot compute next_user up-front + * and expect it to remain valid across calls to + * client code (as the identity of the next user + * in the list may change underneath us). Instead, + * we must compute next_user at the point where we + * are about to cause another iteration of this loop + * (i.e. at the very end, and also at the points where + * continue is used) + */ #ifdef LLCACHE_TRACE if (handle->state != objstate) { @@ -1349,6 +1375,7 @@ nserror llcache_object_notify_users(llcache_object *object) } if (user->queued_for_delete) { + next_user = user->next; llcache_object_user_destroy(user); continue; } @@ -1383,6 +1410,7 @@ nserror llcache_object_notify_users(llcache_object *object) } if (user->queued_for_delete) { + next_user = user->next; llcache_object_user_destroy(user); continue; } @@ -1403,6 +1431,7 @@ nserror llcache_object_notify_users(llcache_object *object) } if (user->queued_for_delete) { + next_user = user->next; llcache_object_user_destroy(user); continue; } @@ -1410,6 +1439,8 @@ nserror llcache_object_notify_users(llcache_object *object) /* No longer the target of an iterator */ user->iterator_target = false; + + next_user = user->next; } return NSERROR_OK; |