Re: [PATCH-for-7.0] qemu/main-loop: Disable block backend global state assertion on Darwin

[Akihiko Odaki <akihiko.odaki@gmail.com>]

On 2022/03/21 23:55, Philippe Mathieu-Daudé wrote:
> From: Philippe Mathieu-Daudé <f4bug@amsat.org>
> 
> Since commit 0439c5a462 ("block/block-backend.c: assertions for
> block-backend") QEMU crashes on Darwin hosts, example on macOS:
> 
>    $ qemu-system-i386
>    Assertion failed: (qemu_in_main_thread()), function blk_all_next, file block-backend.c, line 552.
>    Abort trap: 6
> 
> Looking with lldb:
> 
>    Assertion failed: (qemu_in_main_thread()), function blk_all_next, file block-backend.c, line 552.
>    Process 76914 stopped
>    * thread #1, queue = 'com.apple.main-thread', stop reason = hit program assert
>       frame #4: 0x000000010057c2d4 qemu-system-i386`blk_all_next.cold.1
>    at block-backend.c:552:5 [opt]
>        549    */
>        550   BlockBackend *blk_all_next(BlockBackend *blk)
>        551   {
>    --> 552       GLOBAL_STATE_CODE();
>        553       return blk ? QTAILQ_NEXT(blk, link)
>        554                  : QTAILQ_FIRST(&block_backends);
>        555   }
>    Target 1: (qemu-system-i386) stopped.
> 
>    (lldb) bt
>    * thread #1, queue = 'com.apple.main-thread', stop reason = hit program assert
>       frame #0: 0x00000001908c99b8 libsystem_kernel.dylib`__pthread_kill + 8
>       frame #1: 0x00000001908fceb0 libsystem_pthread.dylib`pthread_kill + 288
>       frame #2: 0x000000019083a314 libsystem_c.dylib`abort + 164
>       frame #3: 0x000000019083972c libsystem_c.dylib`__assert_rtn + 300
>     * frame #4: 0x000000010057c2d4 qemu-system-i386`blk_all_next.cold.1 at block-backend.c:552:5 [opt]
>       frame #5: 0x00000001003c00b4 qemu-system-i386`blk_all_next(blk=<unavailable>) at block-backend.c:552:5 [opt]
>       frame #6: 0x00000001003d8f04 qemu-system-i386`qmp_query_block(errp=0x0000000000000000) at qapi.c:591:16 [opt]
>       frame #7: 0x000000010003ab0c qemu-system-i386`main [inlined] addRemovableDevicesMenuItems at cocoa.m:1756:21 [opt]
>       frame #8: 0x000000010003ab04 qemu-system-i386`main(argc=<unavailable>, argv=<unavailable>) at cocoa.m:1980:5 [opt]
>       frame #9: 0x00000001012690f4 dyld`start + 520
> 
> As we are in passed release 7.0 hard freeze, disable the block
> backend assertion which, while being valuable during development,
> is not helpful to users. We'll restore this assertion immediately
> once 7.0 is released and work on a fix.
> 
> Cc: Kevin Wolf <kwolf@redhat.com>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Peter Maydell <peter.maydell@linaro.org>
> Cc: Emanuele Giuseppe Esposito <eesposit@redhat.com>
> Suggested-by: Akihiko Odaki <akihiko.odaki@gmail.com>
> Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
> ---
>   include/qemu/main-loop.h | 4 ++++
>   1 file changed, 4 insertions(+)
> 
> diff --git a/include/qemu/main-loop.h b/include/qemu/main-loop.h
> index 7a4d6a0920..c27968ce33 100644
> --- a/include/qemu/main-loop.h
> +++ b/include/qemu/main-loop.h
> @@ -270,10 +270,14 @@ bool qemu_mutex_iothread_locked(void);
>   bool qemu_in_main_thread(void);
>   
>   /* Mark and check that the function is part of the global state API. */
> +#ifdef CONFIG_DARWIN

You may use CONFIG_COCOA instead. The assertion can still do its job on 
Darwin if ui/cocoa is not in use.

Also, some code comment is nice to have since the intention is rather 
unclear from the code even though this is temporary and few people would 
stumble upon it.

Regards,
Akihiko Odaki

> +#define GLOBAL_STATE_CODE()
> +#else
>   #define GLOBAL_STATE_CODE()                                         \
>       do {                                                            \
>           assert(qemu_in_main_thread());                              \
>       } while (0)
> +#endif /* CONFIG_DARWIN */
>   
>   /* Mark and check that the function is part of the I/O API. */
>   #define IO_CODE()                                                   \