[FFmpeg-devel] [PATCH] ffplay's primary function is not to trigger OOM killer

[Aurelien Jacobs]

Michael Niedermayer wrote:

> On Fri, Feb 20, 2009 at 12:29:35AM +0100, Aurelien Jacobs wrote:
> > Michael Niedermayer wrote:
> > 
> > > On Thu, Feb 19, 2009 at 11:42:18PM +0100, Aurelien Jacobs wrote:
> > > > Michael Niedermayer wrote:
> > > > 
> > > > > On Thu, Feb 19, 2009 at 10:00:10PM +0100, Aurelien Jacobs wrote:
> > > > > > Hi,
> > > > > > 
> > > > > > Commit r16484 introduced an infinite loop allocating memory in ffplay.
> > > > > > This is very efficient at filling memory and triggering the OOM killer.
> > > > > > The relevant part of the main loop now looks like this:
> > > > > > 
> > > > > >     for(;;) {
> > > > > >         [...]
> > > > > >         if(url_feof(ic->pb)) {
> > > > > >             av_init_packet(pkt);
> > > > > >             [...]
> > > > > >             packet_queue_put(&is->videoq, pkt);
> > > > > >             continue;
> > > > > >         }
> > > > > >         ret = av_read_frame(ic, pkt);
> > > > > >         if (ret < 0) {
> > > > > >             [...]
> > > > > >             break;
> > > > > >         }
> > > > > >         [...]
> > > > > >         packet_queue_put(&is->videoq, pkt);
> > > > > >     }
> > > > > > 
> > > > > > So when the demuxer read the last frame of the stream, the ByteIOContext
> > > > > > reaches EOF but av_read_frame() correctly return a positive value as it
> > > > > > actually read a full frame.
> > > > > > Then at next iteration of the main loop url_feof() is triggered, which
> > > > > > allocate a new packet and go back to the start of the loop, and
> > > > > > triggers url_feof() again, and so on.
> > > > > 
> > > > > try to RTFS again and harder, these kind of bug analysis and fixes is what
> > > > > leds projects to become what mplayer did ...
> > > > 
> > > > try to RTFS a bit more before writing such reply ;-)
> > > 
> > > indeed i should
> > > 
> > > 
> > > > 
> > > > > see, straight before the eof case:
> > > > > 
> > > > >         /* if the queue are full, no need to read more */
> > > > >         if (is->audioq.size > MAX_AUDIOQ_SIZE ||
> > > > >             is->videoq.size > MAX_VIDEOQ_SIZE ||
> > > > >             is->subtitleq.size > MAX_SUBTITLEQ_SIZE) {
> > > > >             /* wait 10 ms */
> > > > >             SDL_Delay(10);
> > > > >             continue;
> > > > >         }
> > > > > 
> > > > > thus the NULL packets are only inserted if the que is not full,
> > > > 
> > > > Right. But the definition of "queue is not full" may not be what you
> > > > would expect.
> > > > 
> > > > > this effectively limits the size and cannot trigger OOM (in theory ...)
> > > > 
> > > > No. This only limits the sum of all pkt.size. But this don't prevent
> > > > adding infinite amount of 0 sized packets. The total size of actual
> > > > data is indeed 0, but the size of the structures containing those
> > > > empty data is enough to fill memory...
> > > 
> > > what about adding sizeof(the struct) to the size used in _put and _get?
> > 
> > That's simple and clean, and that work as well. So it's probably a bit
> > better.
> > 
> > > should also be conceptually be more correct as it better represents the
> > > memory actually used by the que
> > 
> > Indeed.
> > 
> > Patch attached.
> > 
> > Aurel
> > Index: ffplay.c
> > ===================================================================
> > --- ffplay.c	(revision 17459)
> > +++ ffplay.c	(working copy)
> > @@ -282,7 +282,7 @@
> >          q->last_pkt->next = pkt1;
> >      q->last_pkt = pkt1;
> >      q->nb_packets++;
> > -    q->size += pkt1->pkt.size;
> > +    q->size += pkt1->pkt.size + sizeof(*pkt1);
> >      /* XXX: should duplicate packet data in DV case */
> >      SDL_CondSignal(q->cond);
> >  
> 
> you are missing packet_queue_get() that needs to be updated as well or
> the thing will grow until it locks

Ah yes, good catch. I only tested with a small file, so I didn't hit
this situation. Updated patch attached.

Aurel
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