Deadlock in DVBChannel

[Mark Spieth]

there is a suspected deadlock in dvbchannel.

backtrace attached using gcore proposed solution patch attached.

[Mark Spieth]

backtrace

[Mark Spieth]

proposed solution

[Mark Spieth]

symptom is that the backend stops responding.

search for "this=0xa7ba90|mtx = 0xa7bb5[89]"

4 threads want this lock. the one that has it is the TVRec::RunTV TVRec::StartRecording? thread which should be ok Expirer thread and HttpStatus? request handling thread.

it appears as though the RunTV thread is wating for hwlock but cant get it which means one of the other threads may be holding it.

I suspect DVBChannel hwlock should be inited as QMutex::Recursive that should fix this. will test but it doesn't happen often so feedback will take a while.

[Janne Grunau]

Yes, a recursive look would fix it. The locking in DVBChannel is incorrect. Open() calls Close() when InitializeInputs?() fails and both try hold hw_lock.

I'll commit the patch. The recursive Mutex is imho less ugly than the code duplication.

[Janne Grunau]

(In [23838]) DVBChannel: make hw_lock recursive, Fixes #7988

Open() calls Close() in error paths and both try to lock hw_lock Patch by: Mark Spieth

[Janne Grunau]

(In [23839]) Backports [23838] from trunk

DVBChannel: make hw_lock recursive, Fixes #7988 Open() calls Close() in error paths and both try to lock hw_lock Patch by: Mark Spieth