PERFORCE change 125520 for review
Julian Elischer
julian at elischer.org
Mon Sep 17 12:21:02 PDT 2007
Marko Zec wrote:
> On Monday 17 September 2007 20:03:59 Julian Elischer wrote:
>> Marko Zec wrote:
>>> http://perforce.freebsd.org/chv.cgi?CH=125520
>>>
>>> Change 125520 by zec at zec_tpx32 on 2007/08/21 23:51:39
>>>
>>> Given that ng_pipe nodes can be connected into arbitrary
>>> topologies, and therefore it is possible for ngp_rcvdata()
>>> to be recursively called from a single thread, it is
>>> necessary to explicitly allow for the ng_pipe_giant mutex
>>> to be recursively acquireable.
>> OR use a different locking scheme.
>
> That's right, but I'm just wondering is there anything fundamentally
> wrong with lock recursing (both in general as well as in this
> particular case)?
we are trying as a general rule trying to keep lock recursion to an absolute
minimum. It can make debugging other things very hard. and can introduce
bugs that are hard to find..
Generally a bad idea. If you don't know you are recursing, how can you
avoid the problems you don't know about? (sounds silly but..)
>
> Marko
>
>> i.e. reference counts or something.
>>
>>> Affected files ...
>>>
>>> .. //depot/projects/vimage/src/sys/netgraph/ng_pipe.c#2 edit
>>>
>>> Differences ...
>>>
>>> ==== //depot/projects/vimage/src/sys/netgraph/ng_pipe.c#2 (text+ko)
>>> ====
>>>
>>> @@ -1028,7 +1028,7 @@
>>> error = EEXIST;
>>> else {
>>> mtx_init(&ng_pipe_giant, "ng_pipe_giant", NULL,
>>> - MTX_DEF);
>>> + MTX_DEF | MTX_RECURSE);
>>> LIST_INIT(&node_head);
>>> LIST_INIT(&hook_head);
>>> ds_handle = timeout((timeout_t *) &pipe_scheduler,
>
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