Should I delete created coroutines manually?

Should I delete created coroutines manually?

[Coiby Xu]

Hi,

I'm working on vhost-user block device backend [1]. When I tested my
patches on the latest version of QEMU (commit
d0ed6a69d399ae193959225cdeaa9382746c91cc) with --enable-sanitizer turned
on, the follow error will be thrown out,

     ==46631==ERROR: LeakSanitizer: detected memory leaks

     Direct leak of 312 byte(s) in 1 object(s) allocated from:
         #0 0x55d0a7813921 in calloc (qemu/qemu-storage-daemon+0x646921)
         #1 0x7f8bd6f7b591 in g_malloc0 (/usr/lib/libglib-2.0.so.0+0x4f591)
         #2 0x55d0a815f3fb in qemu_coroutine_create qemu/util/qemu-coroutine.c:75:14
         #3 0x55d0a817321e in vu_client_start qemu/util/vhost-user-server.c:225:23
         #4 0x55d0a816fcf3 in vu_accept qemu/util/vhost-user-server.c:341:5
         #5 0x55d0a7f1293f in qio_net_listener_channel_func qemu/io/net-listener.c:54:9
         #6 0x55d0a7efb0f3 in qio_channel_fd_source_dispatch qemu/io/channel-watch.c:84:12
         #7 0x7f8bd6f7e33f in g_main_context_dispatch (/usr/lib/libglib-2.0.so.0+0x5233f)

I have to call qemu_coroutine_delete to eliminate this kind of errors.

I noticed
     make docker-test-clang@ubuntu SHOW_ENV=1 J=12 TARGET_LIST=x86_64-softmmu EXTRA_CONFIGURE_OPTS=--enable-sanitizers"
won't give the above error while
     "make docker-test-debug@fedora TARGET_LIST=x86_64-softmmu J=12" would.

And for older commits like commit eea8f5df4ecc607d64f091b8d916fcc11a697541,
this kind of error won't be shown either.

Is this kind of error true a false positve because "ASan doesn't fully
support makecontext/swapcontext functions and may produce false positives in some cases"?

I don't have sufficient knowledge on QEMU coroutine and ASan to reach a
conclusion. Could anyone enlighten me? Thank you!

[1] https://patchew.org/QEMU/20200614183907.514282-1-coiby.xu@gmail.com/

--
Best regards,
Coiby

Re: Should I delete created coroutines manually?

[Stefan Hajnoczi]

On Mon, Aug 17, 2020 at 2:13 PM Coiby Xu <coiby.xu@gmail.com> wrote:
> I'm working on vhost-user block device backend [1]. When I tested my
> patches on the latest version of QEMU (commit
> d0ed6a69d399ae193959225cdeaa9382746c91cc) with --enable-sanitizer turned
> on, the follow error will be thrown out,
>
>      ==46631==ERROR: LeakSanitizer: detected memory leaks
>
>      Direct leak of 312 byte(s) in 1 object(s) allocated from:
>          #0 0x55d0a7813921 in calloc (qemu/qemu-storage-daemon+0x646921)
>          #1 0x7f8bd6f7b591 in g_malloc0 (/usr/lib/libglib-2.0.so.0+0x4f591)
>          #2 0x55d0a815f3fb in qemu_coroutine_create qemu/util/qemu-coroutine.c:75:14
>          #3 0x55d0a817321e in vu_client_start qemu/util/vhost-user-server.c:225:23
>          #4 0x55d0a816fcf3 in vu_accept qemu/util/vhost-user-server.c:341:5
>          #5 0x55d0a7f1293f in qio_net_listener_channel_func qemu/io/net-listener.c:54:9
>          #6 0x55d0a7efb0f3 in qio_channel_fd_source_dispatch qemu/io/channel-watch.c:84:12
>          #7 0x7f8bd6f7e33f in g_main_context_dispatch (/usr/lib/libglib-2.0.so.0+0x5233f)
>
> I have to call qemu_coroutine_delete to eliminate this kind of errors.

qemu_coroutine_delete() is an internal API and shouldn't be called directly.

If you are sure that the coroutine terminated (returned from its entry
function) then the leak is probably caused by the following:

util/qemu-coroutine.c has a pool of Coroutine objects that are reused.
It's likely that the "leaked" object is in that pool.

I'm surprised that this issue hasn't been reported before, but
release_pool should be cleaned up when the program terminates.

Stefan

Re: Should I delete created coroutines manually?

[Coiby Xu]

On Tue, Aug 18, 2020 at 04:19:58PM +0100, Stefan Hajnoczi wrote:
>On Mon, Aug 17, 2020 at 2:13 PM Coiby Xu <coiby.xu@gmail.com> wrote:
>> I'm working on vhost-user block device backend [1]. When I tested my
>> patches on the latest version of QEMU (commit
>> d0ed6a69d399ae193959225cdeaa9382746c91cc) with --enable-sanitizer turned
>> on, the follow error will be thrown out,
>>
>>      ==46631==ERROR: LeakSanitizer: detected memory leaks
>>
>>      Direct leak of 312 byte(s) in 1 object(s) allocated from:
>>          #0 0x55d0a7813921 in calloc (qemu/qemu-storage-daemon+0x646921)
>>          #1 0x7f8bd6f7b591 in g_malloc0 (/usr/lib/libglib-2.0.so.0+0x4f591)
>>          #2 0x55d0a815f3fb in qemu_coroutine_create qemu/util/qemu-coroutine.c:75:14
>>          #3 0x55d0a817321e in vu_client_start qemu/util/vhost-user-server.c:225:23
>>          #4 0x55d0a816fcf3 in vu_accept qemu/util/vhost-user-server.c:341:5
>>          #5 0x55d0a7f1293f in qio_net_listener_channel_func qemu/io/net-listener.c:54:9
>>          #6 0x55d0a7efb0f3 in qio_channel_fd_source_dispatch qemu/io/channel-watch.c:84:12
>>          #7 0x7f8bd6f7e33f in g_main_context_dispatch (/usr/lib/libglib-2.0.so.0+0x5233f)
>>
>> I have to call qemu_coroutine_delete to eliminate this kind of errors.
>
>qemu_coroutine_delete() is an internal API and shouldn't be called directly.
>
>If you are sure that the coroutine terminated (returned from its entry
>function) then the leak is probably caused by the following:

Thank you for this clue! Yesterday I realized the execution of coroutine
has been yielded since qio_channel_yield is called. Now I give the socket
server enough time to do the clean-up work after the client socket is
closed and the issue is gone.

>
>util/qemu-coroutine.c has a pool of Coroutine objects that are reused.
>It's likely that the "leaked" object is in that pool.
>
>I'm surprised that this issue hasn't been reported before, but
>release_pool should be cleaned up when the program terminates.

I still can't figure out why the issue hasn't been reported before. I guess
I have to put it aside.
>
>Stefan

--
Best regards,
Coiby