[asterisk-dev] tilghman: branch 1.4 r125740 - /branches/1.4/channels/chan_local.c

[Russell Bryant]

On Jun 27, 2008, at 8:19 AM, SVN commits to the Digium repositories  
wrote:

> Author: tilghman
> Date: Fri Jun 27 07:19:39 2008
> New Revision: 125740
>
> URL: http://svn.digium.com/view/asterisk?view=rev&rev=125740
> Log:
> Add proper deadlock avoidance.
> (closes issue #12914)
> Reported by: ozan
> Patches:
>       20080625__bug12914.diff.txt uploaded by Corydon76 (license 14)
> Tested by: ozan
>
> Modified:
>    branches/1.4/channels/chan_local.c
>
> Modified: branches/1.4/channels/chan_local.c
> URL: http://svn.digium.com/view/asterisk/branches/1.4/channels/chan_local.c?view=diff&rev=125740&r1=125739&r2=125740
> = 
> = 
> = 
> = 
> = 
> = 
> = 
> = 
> ======================================================================
> --- branches/1.4/channels/chan_local.c (original)
> +++ branches/1.4/channels/chan_local.c Fri Jun 27 07:19:39 2008
> @@ -186,13 +186,15 @@
> 	while (other && ast_channel_trylock(other)) {
> 		ast_mutex_unlock(&p->lock);
> 		if (us && us_locked) {
> -			ast_channel_unlock(us);
> -		}
> -		usleep(1);
> -		if (us && us_locked) {
> -			ast_channel_lock(us);
> -		}
> -		ast_mutex_lock(&p->lock);
> +			do {
> +				ast_channel_unlock(us);
> +				usleep(1);
> +				ast_channel_lock(us);
> +			} while (ast_mutex_trylock(&p->lock));
> +		} else {
> +			usleep(1);
> +			ast_mutex_lock(&p->lock);
> +		}
> 		other = isoutbound ? p->owner : p->chan;
> 	}
>
> @@ -510,7 +512,12 @@
> 	if (!p)
> 		return -1;
>
> -	ast_mutex_lock(&p->lock);
> +	while (ast_mutex_trylock(&p->lock)) {
> +		ast_channel_unlock(ast);
> +		usleep(1);
> +		ast_channel_lock(ast);
> +	}
> +
> 	isoutbound = IS_OUTBOUND(ast, p);
> 	if (isoutbound) {
> 		const char *status = pbx_builtin_getvar_helper(p->chan,  
> "DIALSTATUS");


As I indicated in another response, this code construct is not correct  
since the channel must always be locked before the pvt.  When going  
that direction, this avoidance code should not be used.  This deadlock  
avoidance is expensive, and should be avoided when unnecessary.

--
Russell Bryant
Senior Software Engineer
Open Source Team Lead
Digium, Inc.