This is a note to let you know that I've just added the patch titled
[media] media/dvb-core: Race condition when writing to CAM
to the 4.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...
The filename of the patch is: media-dvb-core-race-condition-when-writing-to-cam.patch and it can be found in the queue-4.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.
From foo@baz Thu Mar 22 14:57:32 CET 2018
From: Jasmin J jasmin@anw.at Date: Fri, 17 Mar 2017 23:04:20 -0300 Subject: [media] media/dvb-core: Race condition when writing to CAM
From: Jasmin J jasmin@anw.at
[ Upstream commit e7080d4471d805d921a9ea21b32f911a91e248cb ]
It started with a sporadic message in syslog: "CAM tried to send a buffer larger than the ecount size" This message is not the fault itself, but a consecutive fault, after a read error from the CAM. This happens only on several CAMs, several hardware, and of course sporadic.
It is a consecutive fault, if the last read from the CAM did fail. I guess this will not happen on all CAMs, but at least it did on mine. There was a write error to the CAM and during the re-initialization procedure, the CAM finished the last read, although it got a RS.
The write error to the CAM happened because a race condition between HC write, checking DA and FR.
This patch added an additional check for DA(RE), just after checking FR. It is important to read the CAMs status register again, to give the CAM the necessary time for a proper reaction to HC. Please note the description within the source code (patch below).
[mchehab@s-opensource.com: make checkpatch happy]
Signed-off-by: Jasmin jessich jasmin@anw.at Tested-by: Ralph Metzler rjkm@metzlerbros.de Signed-off-by: Mauro Carvalho Chehab mchehab@s-opensource.com Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/media/dvb-core/dvb_ca_en50221.c | 23 +++++++++++++++++++++++ 1 file changed, 23 insertions(+)
--- a/drivers/media/dvb-core/dvb_ca_en50221.c +++ b/drivers/media/dvb-core/dvb_ca_en50221.c @@ -750,6 +750,29 @@ static int dvb_ca_en50221_write_data(str goto exit; }
+ /* + * It may need some time for the CAM to settle down, or there might + * be a race condition between the CAM, writing HC and our last + * check for DA. This happens, if the CAM asserts DA, just after + * checking DA before we are setting HC. In this case it might be + * a bug in the CAM to keep the FR bit, the lower layer/HW + * communication requires a longer timeout or the CAM needs more + * time internally. But this happens in reality! + * We need to read the status from the HW again and do the same + * we did for the previous check for DA + */ + status = ca->pub->read_cam_control(ca->pub, slot, CTRLIF_STATUS); + if (status < 0) + goto exit; + + if (status & (STATUSREG_DA | STATUSREG_RE)) { + if (status & STATUSREG_DA) + dvb_ca_en50221_thread_wakeup(ca); + + status = -EAGAIN; + goto exit; + } + /* send the amount of data */ if ((status = ca->pub->write_cam_control(ca->pub, slot, CTRLIF_SIZE_HIGH, bytes_write >> 8)) != 0) goto exit;
Patches currently in stable-queue which might be from jasmin@anw.at are
queue-4.4/media-dvb-core-race-condition-when-writing-to-cam.patch