Re: [PATCH 3/7] Fixed SVM hang when do failover before PVM crash

[address@hidden]

On 17/06/2021 10:47, Lei Rao wrote:
> From: "Rao, Lei" <lei.rao@intel.com>
>
> This patch fixed as follows:
>      Thread 1 (Thread 0x7f34ee738d80 (LWP 11212)):
>      #0 __pthread_clockjoin_ex (threadid=139847152957184, 
> thread_return=0x7f30b1febf30, clockid=<optimized out>, abstime=<optimized 
> out>, block=<optimized out>) at pthread_join_common.c:145
>      #1 0x0000563401998e36 in qemu_thread_join (thread=0x563402d66610) at 
> util/qemu-thread-posix.c:587
>      #2 0x00005634017a79fa in process_incoming_migration_co (opaque=0x0) at 
> migration/migration.c:502
>      #3 0x00005634019b59c9 in coroutine_trampoline (i0=63395504, i1=22068) at 
> util/coroutine-ucontext.c:115
>      #4 0x00007f34ef860660 in ?? () at 
> ../sysdeps/unix/sysv/linux/x86_64/__start_context.S:91 from 
> /lib/x86_64-linux-gnu/libc.so.6
>      #5 0x00007f30b21ee730 in ?? ()
>      #6 0x0000000000000000 in ?? ()
>
>      Thread 13 (Thread 0x7f30b3dff700 (LWP 11747)):
>      #0  __lll_lock_wait (futex=futex@entry=0x56340218ffa0 
> <qemu_global_mutex>, private=0) at lowlevellock.c:52
>      #1  0x00007f34efa000a3 in _GI__pthread_mutex_lock (mutex=0x56340218ffa0 
> <qemu_global_mutex>) at ../nptl/pthread_mutex_lock.c:80
>      #2  0x0000563401997f99 in qemu_mutex_lock_impl (mutex=0x56340218ffa0 
> <qemu_global_mutex>, file=0x563401b7a80e "migration/colo.c", line=806) at 
> util/qemu-thread-posix.c:78
>      #3  0x0000563401407144 in qemu_mutex_lock_iothread_impl 
> (file=0x563401b7a80e "migration/colo.c", line=806) at 
> /home/workspace/colo-qemu/cpus.c:1899
>      #4  0x00005634017ba8e8 in colo_process_incoming_thread 
> (opaque=0x563402d664c0) at migration/colo.c:806
>      #5  0x0000563401998b72 in qemu_thread_start (args=0x5634039f8370) at 
> util/qemu-thread-posix.c:519
>      #6  0x00007f34ef9fd609 in start_thread (arg=<optimized out>) at 
> pthread_create.c:477
>      #7  0x00007f34ef924293 in clone () at 
> ../sysdeps/unix/sysv/linux/x86_64/clone.S:95
>
>      The QEMU main thread is holding the lock:
>      (gdb) p qemu_global_mutex
>      $1 = {lock = {_data = {lock = 2, __count = 0, __owner = 11212, __nusers 
> = 9, __kind = 0, __spins = 0, __elision = 0, __list = {_prev = 0x0, __next = 
> 0x0}},
>       __size = "\002\000\000\000\000\000\000\000\314+\000\000\t", '\000' 
> <repeats 26 times>, __align = 2}, file = 0x563401c07e4b "util/main-loop.c", 
> line = 240,
>      initialized = true}
>
>  From the call trace, we can see it is a deadlock bug. and the QEMU main 
> thread holds the global mutex to wait until the COLO thread ends. and the 
> colo thread
> wants to acquire the global mutex, which will cause a deadlock. So, we should 
> release the qemu_global_mutex before waiting colo thread ends.
>
> Signed-off-by: Lei Rao <lei.rao@intel.com>
Reviewed-by: Li Zhijian <lizhijian@cn.fujitsu.com>


> ---
>   migration/migration.c | 2 ++
>   1 file changed, 2 insertions(+)
>
> diff --git a/migration/migration.c b/migration/migration.c
> index c2c84c7..6debb8b 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -593,8 +593,10 @@ static void process_incoming_migration_co(void *opaque)
>           mis->have_colo_incoming_thread = true;
>           qemu_coroutine_yield();
>   
> +        qemu_mutex_unlock_iothread();
>           /* Wait checkpoint incoming thread exit before free resource */
>           qemu_thread_join(&mis->colo_incoming_thread);
> +        qemu_mutex_lock_iothread();
>           /* We hold the global iothread lock, so it is safe here */
>           colo_release_ram_cache();
>       }