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RE: RFC: bsd_tcpip patch on synch.c
- From: Bernd Edlinger <bernd dot edlinger at hotmail dot de>
- To: "ecos-devel at ecos dot sourceware dot org" <ecos-devel at ecos dot sourceware dot org>
- Date: Thu, 27 Jun 2013 14:51:01 +0200
- Subject: RE: RFC: bsd_tcpip patch on synch.c
- References: <51CC0714 dot 6040805 at televic dot com>,<DUB124-W44EE5E989F221552E035FDE4750 at phx dot gbl>
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
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