Re: [PATCH-for-7.0 v3] qemu/main-loop: Disable block backend global state assertion on Cocoa

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

Reviewed-by: Akihiko Odaki <akihiko.odaki@gmail.com>

On 2022/03/26 3:37, Philippe Mathieu-Daudé wrote:
> From: Philippe Mathieu-Daudé <f4bug@amsat.org>
> 
> Since commit 0439c5a462 ("block/block-backend.c: assertions for
> block-backend") QEMU crashes when using Cocoa 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>
> ---
> v3: Reword (Akihiko)
> ---
>   include/qemu/main-loop.h | 13 +++++++++++++
>   1 file changed, 13 insertions(+)
> 
> diff --git a/include/qemu/main-loop.h b/include/qemu/main-loop.h
> index 7a4d6a0920..89bd9edefb 100644
> --- a/include/qemu/main-loop.h
> +++ b/include/qemu/main-loop.h
> @@ -270,10 +270,23 @@ 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_COCOA
> +/*
> + * When using the Cocoa UI, addRemovableDevicesMenuItems() is called from
> + * a thread different from the QEMU main thread and can not take the BQL,
> + * triggering this assertions in the block layer (commit 0439c5a462).
> + * As the Cocoa fix is not trivial, disable this assertion for the v7.0.0
> + * release (when using Cocoa); we will restore it immediately after the
> + * release.
> + * This issue is tracked as https://gitlab.com/qemu-project/qemu/-/issues/926
> + */
> +#define GLOBAL_STATE_CODE()
> +#else
>   #define GLOBAL_STATE_CODE()                                         \
>       do {                                                            \
>           assert(qemu_in_main_thread());                              \
>       } while (0)
> +#endif /* CONFIG_COCOA */
>   
>   /* Mark and check that the function is part of the I/O API. */
>   #define IO_CODE()                                                   \