Re: [PATCH] Mantis: append tasklet maintenance for DVB stream delivery

[Marko Ristola <marko.ristola@kolumbus.fi>]

Resending into linux-media, for confirming authorship:

I have personally done this patch.
Acked-by: Marko M Ristola <marko.ristola@kolumbus.fi>

Regards,
Marko

20.06.2010 16:51, Bjørn Mork kirjoitti:
> Note that mantis_core_exit() is never called.  Unless I've missed
> something, the drivers/media/dvb/mantis/mantis_core.{h,c} files can
> just be deleted.  They look like some development leftovers?
>
>    
I see. mantis_core.ko kernel module exists though.
Maybe the mantis/Makefile references for mantis_core.c, mantis.c and hopper.c are just some leftovers too.

I moved tasklet_enable/disable calls into mantis_dvb.c where almost all other tasklet code is located.

So the following reasoning still holds:

1. dvb_dmxdev_filter_stop() calls mantis_dvb_stop_feed: mantis_dma_stop()
2. dvb_dmxdev_filter_stop() calls release_ts_feed() or some other filter freeing function.
3. tasklet: mantis_dma_xfer calls dvb_dmx_swfilter to copy DMA buffer's content into freed memory, accessing freed spinlocks.
This case might occur while tuning into another frequency.
Perhaps cdurrhau has found some version from this bug at http://www.linuxtv.org/pipermail/linux-dvb/2010-June/032688.html:
> This is what I get on the remote console via IPMI:
> 40849.442492] BUG: soft lockup - CPU#2 stuck for 61s! [section
> handler:4617]


New reasoning for the patch (same as the one above, but from higher level):
After dvb-core has called mantis-fe->stop_feed(dvbdmxfeed) the last time (count to zero),
no data should ever be copied with dvb_dmx_swfilter() by a tasklet: the target structure might be in an unusable state.
Caller of mantis_fe->stop_feed() assumes that feeding is stopped after stop_feed() has been called, ie. dvb_dmx_swfilter()
isn't running, and won't be called.

There is a risk that dvb_dmx_swfilter() references freed resources (memory or spinlocks or ???) causing instabilities.
Thus tasklet_disable(&mantis->tasklet) must be called inside of mantis-fe->stop_feed(dvbdmxfeed) when necessary.

Signed-off-by: Marko Ristola <marko.ristola@kolumbus.fi>

Marko

diff --git a/drivers/media/dvb/mantis/mantis_dvb.c b/drivers/media/dvb/mantis/mantis_dvb.c
index 99d82ee..a9864f7 100644
--- a/drivers/media/dvb/mantis/mantis_dvb.c
+++ b/drivers/media/dvb/mantis/mantis_dvb.c
@@ -117,6 +117,7 @@ static int mantis_dvb_start_feed(struct dvb_demux_feed *dvbdmxfeed)
     if (mantis->feeds == 1)     {
         dprintk(MANTIS_DEBUG, 1, "mantis start feed & dma");
         mantis_dma_start(mantis);
+        tasklet_enable(&mantis->tasklet);
     }

     return mantis->feeds;
@@ -136,6 +137,7 @@ static int mantis_dvb_stop_feed(struct dvb_demux_feed *dvbdmxfeed)
     mantis->feeds--;
     if (mantis->feeds == 0) {
         dprintk(MANTIS_DEBUG, 1, "mantis stop feed and dma");
+        tasklet_disable(&mantis->tasklet);
         mantis_dma_stop(mantis);
     }

@@ -216,6 +218,7 @@ int __devinit mantis_dvb_init(struct mantis_pci *mantis)

     dvb_net_init(&mantis->dvb_adapter, &mantis->dvbnet, &mantis->demux.dmx);
     tasklet_init(&mantis->tasklet, mantis_dma_xfer, (unsigned long) mantis);
+    tasklet_disable(&mantis->tasklet);
     if (mantis->hwconfig) {
         result = config->frontend_init(mantis, mantis->fe);
         if (result < 0) {