[Qemu-devel] [PULL 01/12] migration: multifd_send_thread always post p->sem_sync when error happen

["Dr. David Alan Gilbert (git)" <dgilbert@redhat.com>]

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>
Message-Id: <1567044996-2362-1-git-send-email-ivanren@tencent.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
---
 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);
     }
 
-- 
2.21.0