Opened 7 years ago

Closed 7 years ago

#11082 closed Bug Report - Hang/Deadlock (Invalid)

Deadlock when entering LiveTV

Reported by: Kenni Lund [kenni a kelu dot dk] Owned by:
Priority: minor Milestone: unknown
Component: MythTV - General Version: Master Head
Severity: medium Keywords:
Cc: Ticket locked: no

Description

I'm seeing this deadlock regularly after upgrading to pre0.26 from 0.25-fixes. This time I got a chance to attach gdb to the mythbackend process and collect a backtrace before restarting it. Unfortunately I didn't get the frontend backtrace as it didn't have any symbols installed.

Symptom: When I enter LiveTV on a frontend, the screen remains black with no sound and no error messages of any kind. Performing a tcpdump on the frontend reveals that no data are received from the backend at this point. Looking at the backend reveals that the backend happily records from my HDHR to a LiveTV file, but it doesn't stream anything to the frontend.

I can exit back to the main menu with no issues and start LiveTV again afterwards, again resulting in a black screen and the backend recording to a new LiveTV file and not streaming anything to the frontend.

The backend log doesn't contain even a single line from the moment when I trigger LiveTV on the frontend. The frontend does produce log-entries, but no obvious errors are given (see attached file).

Restarting the backend fixes the issue.

I don't mind compiling a debug build or running with specific verbose options if needed - just ping me.

Version: v0.26-rc2-2-ga625725

Attachments (2)

bt.txt (60.5 KB) - added by Kenni Lund [kenni a kelu dot dk] 7 years ago.
mythfrontend_8_minutes_of_LiveTV_with_black_screen.txt (4.4 KB) - added by Kenni Lund [kenni a kelu dot dk] 7 years ago.

Download all attachments as: .zip

Change History (3)

Changed 7 years ago by Kenni Lund [kenni a kelu dot dk]

Attachment: bt.txt added

Changed 7 years ago by Kenni Lund [kenni a kelu dot dk]

comment:1 Changed 7 years ago by Kenni Lund [kenni a kelu dot dk]

Resolution: Invalid
Status: newclosed

The real issue causing the "deadlock" is that mythfrontend doesn't support suspend-to-RAM. I already knew that and had a suspend/wakeup script to restart the frontend. For other unrelated reasons, the restart script stopped working and hence the frontend wasn't restarted on wakeup. I never noticed as the frontend usually starts up before the TV is ready.

Restarting the backend reestablished the connection with the frontend, but the real issue was the frontend being in an unconsistent state.

The lack of logs on the backend was apparently also unrelated and was caused by a crashed mythlogserver:

mythlogserver[394]: segfault at 63 ip 0000000000000063 sp 00007f459904a678 error 14 in mythlogserver[400000+3000]

I'll enable core dumps and post a separate ticket if mythlogserver crashes again.

Sorry about the noise.

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