[media_addon_server] crash in BPrivate::SharedBufferList::Lock

[diver]

I restarted media services (from Media preflet) while having MediaPlayer opened (dunno if it's related) and that crashed media_addon_server.

This was in VMware Fusion without any sound cards detected by Haiku, i.e. OpenSound not installed.

Debug information for team /boot/system/servers/media_addon_server (1790):
CPU(s): 2x Intel Core™ i7-3635QM
Memory: 1.46 GiB total, 538.89 MiB used
Haiku revision: hrev53693 Jan  7 2020 07:16:18 (x86_64)

Active Threads:
	thread 1790: media_addon_server (main)
	thread 1808: _BMediaRoster_ 
	thread 1810: media_addon_server control 
	thread 1811: System clock control 
	thread 2571: team 1790 debug task 
	thread 1843: Audio Mixer control 
		state: Exception (Segment violation)

		Frame		IP			Function Name
		-----------------------------------------------
		0x7f5a39ac9de0	0xba403bc981	BPrivate::SharedBufferList::Lock() + 0x11 
			Disassembly:
				BPrivate::SharedBufferList::Lock():
				0x000000ba403bc970:               55  push %rbp
				0x000000ba403bc971:       ba01000000  mov $0x1, %edx
				0x000000ba403bc976:           4889e5  mov %rsp, %rbp
				0x000000ba403bc979:               53  push %rbx
				0x000000ba403bc97a:           4889fb  mov %rdi, %rbx
				0x000000ba403bc97d:         4883ec08  sub $0x8, %rsp
				0x000000ba403bc981:       f00fc15704  lock xadd %edx, 0x4(%rdi) <--

			Frame memory:
				[0x7f5a39ac9dc0]  ...9Z......T....   e0 9d ac 39 5a 7f 00 00 80 a8 df 54 d6 01 00 00
				[0x7f5a39ac9dd0]   ..9Z...;.;@....   20 9e ac 39 5a 7f 00 00 3b cd 3b 40 ba 00 00 00
		0x7f5a39ac9e30	0xba403bcd36	BPrivate::SharedBufferList::RecycleBuffer(BBuffer*) + 0x26 
		0x7f5a39ac9e50	0xba40397f43	BMediaEventLooper::DispatchEvent(media_timed_event const*, long, bool) + 0x13 
		0x7f5a39ac9f40	0xba40398237	BMediaEventLooper::ControlLoop() + 0x257 
		0x7f5a39ac9f60	0xba40397d3c	BMediaEventLooper::_ControlThreadStart(void*) + 0x1c 
		0x7f5a39ac9f80	0x54438002f7	thread_entry + 0x17 
		00000000	0x7fc5c667d260	commpage_thread_exit + 0 

[diver]

Still here in hrev53868.

[pulkomandy]

Fixed in hrev53876.

[nielx]

Assign tickets with status=closed and resolution=fixed within the R1/beta2 development window to the R1/beta2 Milestone