Re: (ITS#6783) back-monitor cache/mutex problem

[hyc@symas.com]

h.b.furuseth@usit.uio.no wrote:
> Full_Name: Hallvard B Furuseth
> Version: HEAD
> OS: Linux x86_64
> URL:
> Submission from: (NULL) (193.157.198.89)
> Submitted by: hallvard
>
>
> Core dump in back-monitor with LDAP_THREAD_DEBUG when I hit ^C:
>
> 	ASSERT_OWNER( mutex, "ldap_pvt_thread_mutex_unlock" );

I see this too. The Abandon loop's logic is backwards. It's looping from the 
current entry to the end of the list and releasing those entries, when it 
should only be reasling from the head of the list to the current entry. (I.e., 
everything on the tail of the list has not yet been locked by this thread.)

I'll commit a fix shortly.
>
> #2 ldap_pvt_thread_mutex_unlock (mutex=0x1a526c0) at thr_debug.c:1031
> #3 monitor_cache_release (mi=0x92c8c0, e=0x19ec7f8) at cache.c:389
> #4 monitor_send_children (op=0x236bcb0, rs=0x7f54ce4eea40,
>                            e_parent=0x19ec758, sub=1) at search.c:97
> #5 monitor_back_search (op=0x236bcb0, rs=0x7f54ce4eea40) at search.c:245
> #6 fe_op_search (op=0x236bcb0, rs=0x7f54ce4eea40) at search.c:372
>
> That's the o_abandon branch in monitor_send_children().
>
> I copied the loop out of the o_abandon branch.  test036 crashed with
> what I assume is the same problem.  No need to hit ^C at the right time:
>
> Index: back-monitor/search.c
> @@ -89,2 +89,9 @@ monitor_send_children(
>
> +		if ( nonvolatile == 0&&  (e_tmp = e) != NULL ) {
> +			do {
> +				mp = e_tmp->e_private;
> +				LDAP_PVT_THREAD_ASSERT_MUTEX_OWNER(&mp->mp_mutex );
> +			} while ( (e_tmp = mp->mp_next)&&  e_tmp != e_nonvolatile );
> +		}
> +
>   		if ( op->o_abandon ) {
>
> There is a similar loop further down, I didn't look at that one.
>
> Variables at the crash:
>
> e     == e_nonvolatile
> e_tmp == ((monitor_entry_t *) e->e_private)->mp_next
>
> *(monitor_entry_t *) e->e_private == {
>      mp_mutex = {...}, mp_next = 0x261b2a8, mp_children = 0x261b668,
>      mp_info = 0x8f21c0, mp_flags = 32, mp_cb = 0x0
> }
>
> *(monitor_entry_t *) e_tmp->e_private == {
>      mp_mutex = {...}, mp_next = 0x261b2f8, mp_children = 0x261ba28,
>      mp_info = 0x8f2258, mp_flags = 128, mp_cb = 0x0
> }
>
>


-- 
   -- Howard Chu
   CTO, Symas Corp.           http://www.symas.com
   Director, Highland Sun     http://highlandsun.com/hyc/
   Chief Architect, OpenLDAP  http://www.openldap.org/project/