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RE: RFC: bsd_tcpip patch on synch.c


Hi Jürgen,


the variant with cyg_mutex_trylock is like busy waiting, and
should be reverted. But I agree that the
"while (!cyg_mutex_lock()) continue;"
construct is somehow really bad style.

I do not think that cyg_mutex_lock can ever return false,
unless the spl_mutex is completely invalid.

If you really expect cyg_mutex_lock to ever return false,
then the right thing to do would be to assert(false)
and print a callstack or directly enter the debugger.


Regards
Bernd Edlinger.


> From: J.Lambrecht@TELEVIC.com
> To: ecos-devel@ecos.sourceware.org
> CC: bernd.edlinger@hotmail.de
> Date: Thu, 27 Jun 2013 11:34:12 +0200
> Subject: RFC: bsd_tcpip patch on synch.c
> 
> Hello,
> 
> The patch below we already use since 2009. But I did not code the patch, 
> so I do not know what problem it solves. Here are our CVS logs about the 
> patch:
> 
> - To avoid deadlock on mutex 'splx_mutex', I changed 'cyg_mutex_lock' 
> into 'cyg_mutex_trylock'.
> - Add 'trylock' and 'cyg_thread_delay' to spl_any() in order to handle 
> the deadlock issue on the mutex 'splx_mutex'
> 
> I am applying the patches from Bernd Edlinger 
> (http://bugs.ecos.sourceware.org/show_bug.cgi?id=1001656)(to fix an 
> anoying problem "packet loss every 20 minutes when ARP timeout expires" 
> and to add raw packets).
> And I wonder if this patch (below) is still valid?
> --------------------------------------------------------------------------------
> Index: net/bsd_tcpip/current/src/ecos/synch.c
> ===================================================================
> RCS file: /cvs/ecos/ecos-opt/net/net/bsd_tcpip/current/src/ecos/synch.c,v
> retrieving revision 1.3
> diff -u -5 -p -r1.3 synch.c
> --- net/bsd_tcpip/current/src/ecos/synch.c      29 Jan 2009 17:49:56 
> -0000      1.3
> +++ net/bsd_tcpip/current/src/ecos/synch.c      27 Jun 2013 09:12:54 -0000
> @@ -115,12 +115,14 @@ static volatile cyg_handle_t splx_thread
>   static inline cyg_uint32
>   spl_any( cyg_uint32 which )
>   {
>       cyg_uint32 old_spl = spl_state;
>       if ( cyg_thread_self() != splx_thread ) {
> -        while ( !cyg_mutex_lock( &splx_mutex ) )
> +        while ( !cyg_mutex_trylock( &splx_mutex ) ) {
> +          cyg_thread_delay(1);
>               continue;
> +        }
>           old_spl = 0; // Free when we unlock this context
>           CYG_ASSERT( 0 == splx_thread, "Thread still owned" );
>           CYG_ASSERT( 0 == spl_state, "spl still set" );
>           splx_thread = cyg_thread_self();
>       }
> --------------------------------------------------------------------------------
> Kind regards,
> Jürgen
> 
> -- 
> Jürgen Lambrecht
> R&D Associate
> Mobile: +32 499 644 531
> Tel: +32 (0)51 303045    Fax: +32 (0)51 310670
> http://www.televic-rail.com
> Televic Rail NV - Leo Bekaertlaan 1 - 8870 Izegem - Belgium
> Company number 0825.539.581 - RPR Kortrijk 		 	   		  

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