On 05/07/16 15:26, Mauro Carvalho Chehab wrote:
Em Sat, 7 May 2016 10:22:35 -0300
Mauro Carvalho Chehab <mchehab@xxxxxxxxxxxxxxx> escreveu:
Hi Soeren,
Em Sun, 7 Feb 2016 20:22:36 +0100
Soeren Moch <smoch@xxxxxx> escreveu:
On 27.12.2015 21:41, Soeren Moch wrote:
Implement memory barriers according to Documentation/circular-buffers.txt:
- use smp_store_release() to update ringbuffer read/write pointers
- use smp_load_acquire() to load write pointer on reader side
- use ACCESS_ONCE() to load read pointer on writer side
This fixes data stream corruptions observed e.g. on an ARM Cortex-A9
quad core system with different types (PCI, USB) of DVB tuners.
Signed-off-by: Soeren Moch <smoch@xxxxxx>
Cc: stable@xxxxxxxxxxxxxxx # 3.14+
Mauro,
any news or comments on this?
Since this is a real fix for broken behaviour, can you pick this up, please?
The problem here is that I'm very reluctant to touch at the DVB core
without doing some tests myself, as things like locking can be
very sensible.
In addition, it is good if other DVB developers could also test it.
Even being sent for some time, until now, nobody else tested it.
I know that people from the german vdrportal.de also use this patch
for quite some time now. Unfortunately they are not active on the
linux-media mailing list.
I'll try to find some time to take a look on it for Kernel 4.8,
but I'd like to reproduce the bug locally.
Could you please provide me enough info to reproduce it (and
eventually some test MPEG-TS where you know this would happen)?
I have two DekTek RF generators here, so I should be able to
play such TS and see what happens with and without the patch
on x86, arm32 and arm64.
Ah, forgot to mention, but checkpatch.pl wants comments for the memory
barriers:
OK, when I wrote this patch (linux-4.4-rc6) checkpatch.pl did not
complain about missing comments. I will send a version 2 of this
patch to address these warnings.
Regards,
Soeren
WARNING: memory barrier without comment
#52: FILE: drivers/media/dvb-core/dvb_ringbuffer.c:58:
+ return (rbuf->pread == smp_load_acquire(&rbuf->pwrite));
WARNING: memory barrier without comment
#70: FILE: drivers/media/dvb-core/dvb_ringbuffer.c:79:
+ avail = smp_load_acquire(&rbuf->pwrite) - rbuf->pread;
WARNING: memory barrier without comment
#79: FILE: drivers/media/dvb-core/dvb_ringbuffer.c:89:
+ smp_store_release(&rbuf->pread, smp_load_acquire(&rbuf->pwrite));
WARNING: memory barrier without comment
#87: FILE: drivers/media/dvb-core/dvb_ringbuffer.c:96:
+ smp_store_release(&rbuf->pread, 0);
WARNING: memory barrier without comment
#88: FILE: drivers/media/dvb-core/dvb_ringbuffer.c:97:
+ smp_store_release(&rbuf->pwrite, 0);
WARNING: memory barrier without comment
#97: FILE: drivers/media/dvb-core/dvb_ringbuffer.c:123:
+ smp_store_release(&rbuf->pread, 0);
WARNING: memory barrier without comment
#103: FILE: drivers/media/dvb-core/dvb_ringbuffer.c:128:
+ smp_store_release(&rbuf->pread, (rbuf->pread + todo) % rbuf->size);
WARNING: memory barrier without comment
#112: FILE: drivers/media/dvb-core/dvb_ringbuffer.c:143:
+ smp_store_release(&rbuf->pread, 0);
WARNING: memory barrier without comment
#117: FILE: drivers/media/dvb-core/dvb_ringbuffer.c:147:
+ smp_store_release(&rbuf->pread, (rbuf->pread + todo) % rbuf->size);
WARNING: memory barrier without comment
#126: FILE: drivers/media/dvb-core/dvb_ringbuffer.c:162:
+ smp_store_release(&rbuf->pwrite, 0);
WARNING: memory barrier without comment
#130: FILE: drivers/media/dvb-core/dvb_ringbuffer.c:165:
+ smp_store_release(&rbuf->pwrite, (rbuf->pwrite + todo) % rbuf->size);
WARNING: memory barrier without comment
#139: FILE: drivers/media/dvb-core/dvb_ringbuffer.c:185:
+ smp_store_release(&rbuf->pwrite, 0);
WARNING: memory barrier without comment
#145: FILE: drivers/media/dvb-core/dvb_ringbuffer.c:190:
+ smp_store_release(&rbuf->pwrite, (rbuf->pwrite + todo) % rbuf->size);
Thanks,
Mauro
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