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

[Juan Quintela <quintela@redhat.com>]

Ivan Ren <renyime@gmail.com> wrote:
> From: Ivan Ren <ivanren@tencent.com>
>
> 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 <ivanren@tencent.com>

Reviewed-by: Juan Quintela <quintela@redhat.com>