Add a lock and unlock prior to the destruction of the chanspy_ds

lock to ensure that no other threads still have it locked. While
this should not happen under normal circumstances, it appears that
if the spyer and spyee hang up at nearly the same time, the following
may occur.

1. ast_channel_free is called on the spyee's channel.
2. The chanspy datastore is removed from the spyee's channel in
   ast_channel_free.
3. In the spyer's thread, the spyer attempts to remove and destroy the datastore
   from the spyee channel, but the datastore has already been removed in step 2,
   so the spyer continues in the code.
4. The spyee's thread continues and calls the datastore's destroy callback,
   chanspy_ds_destroy. This involves locking the chanspy_ds.
5. Now the spyer attempts to destroy the chanspy_ds lock. The problem is that in step 4,
   the spyee has locked this lock, meaning that the spyer is attempting to destroy a lock
   which is currently locked by another thread.

The backtrace provided in issue #12969 supports the idea that this is possible
(and has even occurred). This commit does not close the issue, but should help
in preventing one type of crash associated with the use of app_chanspy.

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.4@138886 65c4cc65-6c06-0410-ace0-fbb531ad65f3

diff --git a/apps/app_chanspy.c b/apps/app_chanspy.c
index 80af5b234b291c78170e16645e509778e112f941..aba4c3a52a06e8e5ccc22df9d17f263d3651f001 100644 (file)
--- a/apps/app_chanspy.c
+++ b/apps/app_chanspy.c
@@ -674,6 +674,8 @@ static int common_exec(struct ast_channel *chan, const struct ast_flags *flags,
 
        ast_channel_setoption(chan, AST_OPTION_TXGAIN, &zero_volume, sizeof(zero_volume), 0);
 
+       ast_mutex_lock(&chanspy_ds.lock);
+       ast_mutex_unlock(&chanspy_ds.lock);
        ast_mutex_destroy(&chanspy_ds.lock);
 
        return res;