Re: [Qemu-devel] [PATCH] migration: multifd_send_thread always post p->sem_sync when error happen

[Dr. David Alan Gilbert]

Queued

* Ivan Ren (address@hidden) wrote:
> From: Ivan Ren <address@hidden>
> 
> When encounter error, multifd_send_thread should always notify who pay
> attention to it before exit. Otherwise it may block migration_thread
> at multifd_send_sync_main forever.
> 
> Error as follow:
> -------------------------------------------------------------------------------
>  (gdb) bt
>  #0  0x00007f4d669dfa0b in do_futex_wait.constprop.1 () from 
> /lib64/libpthread.so.0
>  #1  0x00007f4d669dfa9f in __new_sem_wait_slow.constprop.0 () from 
> /lib64/libpthread.so.0
>  #2  0x00007f4d669dfb3b in sem_wait@@GLIBC_2.2.5 () from 
> /lib64/libpthread.so.0
>  #3  0x0000562ccf0a5614 in qemu_sem_wait (sem=sem@entry=0x562cd1b698e8) at 
> util/qemu-thread-posix.c:319
>  #4  0x0000562ccecb4752 in multifd_send_sync_main (rs=<optimized out>) at 
> /qemu/migration/ram.c:1099
>  #5  0x0000562ccecb95f4 in ram_save_iterate (f=0x562cd0ecc000, 
> opaque=<optimized out>) at /qemu/migration/ram.c:3550
>  #6  0x0000562ccef43c23 in qemu_savevm_state_iterate (f=0x562cd0ecc000, 
> postcopy=false) at migration/savevm.c:1189
>  #7  0x0000562ccef3dcf3 in migration_iteration_run (s=0x562cd09fabf0) at 
> migration/migration.c:3131
>  #8  migration_thread (opaque=opaque@entry=0x562cd09fabf0) at 
> migration/migration.c:3258
>  #9  0x0000562ccf0a4c26 in qemu_thread_start (args=<optimized out>) at 
> util/qemu-thread-posix.c:502
>  #10 0x00007f4d669d9e25 in start_thread () from /lib64/libpthread.so.0
>  #11 0x00007f4d6670635d in clone () from /lib64/libc.so.6
>  (gdb) f 4
>  #4  0x0000562ccecb4752 in multifd_send_sync_main (rs=<optimized out>) at 
> /qemu/migration/ram.c:1099
>  1099         qemu_sem_wait(&p->sem_sync);
>  (gdb) list
>  1094     }
>  1095     for (i = 0; i < migrate_multifd_channels(); i++) {
>  1096         MultiFDSendParams *p = &multifd_send_state->params[i];
>  1097
>  1098         trace_multifd_send_sync_main_wait(p->id);
>  1099         qemu_sem_wait(&p->sem_sync);
>  1100     }
>  1101     trace_multifd_send_sync_main(multifd_send_state->packet_num);
>  1102 }
>  1103
>  (gdb) p i
>  $1 = 0
>  (gdb)  p multifd_send_state->params[0].pending_job
>  $2 = 2    //It means the job before MULTIFD_FLAG_SYNC has already fail
>  (gdb)  p multifd_send_state->params[0].quit
>  $3 = true
> 
> Signed-off-by: Ivan Ren <address@hidden>
> ---
>  migration/ram.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/migration/ram.c b/migration/ram.c
> index b01a37e7ca..0047286b7e 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -1112,6 +1112,7 @@ static void *multifd_send_thread(void *opaque)
>      rcu_register_thread();
>  
>      if (multifd_send_initial_packet(p, &local_err) < 0) {
> +        ret = -1;
>          goto out;
>      }
>      /* initial packet */
> @@ -1179,9 +1180,7 @@ out:
>       * who pay attention to me.
>       */
>      if (ret != 0) {
> -        if (flags & MULTIFD_FLAG_SYNC) {
> -            qemu_sem_post(&p->sem_sync);
> -        }
> +        qemu_sem_post(&p->sem_sync);
>          qemu_sem_post(&multifd_send_state->channels_ready);
>      }
>  
> -- 
> 2.17.2 (Apple Git-113)
> 
> 
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK