Re: [Qemu-devel] [PATCH v13 11/12] migration: Remove not needed semaphore and quit

[Juan Quintela <quintela@redhat.com>]

"Dr. David Alan Gilbert" <dgilbert@redhat.com> wrote:
> * Juan Quintela (quintela@redhat.com) wrote:
>> "Dr. David Alan Gilbert" <dgilbert@redhat.com> wrote:
>> > * Juan Quintela (quintela@redhat.com) wrote:
>> >> "Dr. David Alan Gilbert" <dgilbert@redhat.com> wrote:
>> >> > * Juan Quintela (quintela@redhat.com) wrote:
>> >> >> We know quit closing the QIO.

...
>> > Two questions from that then:
>> >   a) Are you sure it's safe to close the qio_channel while another
>> > thread is in qio_channel_read_all_eof?  Is it really defined that it
>> > causes the other thread to exit with an error;  close() in some stuff
>> > frees data structures that the other thread is still reading; that's
>> > why I've used shutdown(2) in the past rather than close on fd's
>> 
>> Dunno if it is safe (I think it is), but I agree that shutdown will also
>> get what I need.
>> 
>> >   b) I don't think your answer explains why it's an object_unref?
>> 
>> That is the standard way to closing qios to not have to take into
>> account who have it oppened.  See previous paragraph, it is better to
>> use shutdown, done.
>
> OK, great;  I suspect it's unsafe because as soon as you do the unref
> it could free the object; actually you should have a ref from each of
> the threads to sotp it being freed while they use it.
>
> Dave
>
>> Thanks, Juan.
>> 
>> > Dave
>> >
>> >> Later, Juan.
>> > --
>> > Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
> --
> Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK

What do you think about this, to avoid me resend the whole series?

>From e03d77de1ca179fa0168cead7c23cfeae57f1787 Mon Sep 17 00:00:00 2001
From: Juan Quintela <quintela@redhat.com>
Date: Wed, 18 Apr 2018 00:49:19 +0200
Subject: [PATCH 17/18] migration: Remove not needed semaphore and quit

We know quit with shutdwon in the QIO.

Signed-off-by: Juan Quintela <quintela@redhat.com>
--
Add comment
Use shutdown() instead of unref()
---
 migration/ram.c | 14 +++++---------
 1 file changed, 5 insertions(+), 9 deletions(-)

diff --git a/migration/ram.c b/migration/ram.c
index 2c3a452a7d..be5d26f4cb 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -594,14 +594,10 @@ typedef struct {
     QemuThread thread;
     /* communication channel */
     QIOChannel *c;
-    /* sem where to wait for more work */
-    QemuSemaphore sem;
     /* this mutex protects the following parameters */
     QemuMutex mutex;
     /* is this channel thread running */
     bool running;
-    /* should this thread finish */
-    bool quit;
     /* array of pages to receive */
     MultiFDPages_t *pages;
     /* packet allocated len */
@@ -1152,8 +1148,11 @@ static void multifd_recv_terminate_threads(Error *err)
         MultiFDRecvParams *p = &multifd_recv_state->params[i];
 
         qemu_mutex_lock(&p->mutex);
-        p->quit = true;
-        qemu_sem_post(&p->sem);
+        /* We could arrive here for two reasons:
+           - normal quit, i.e. everything went fine, just finished
+           - error quit: We close the channels so the channel threads
+             finish the qio_channel_read_all_eof() */
+        qio_channel_shutdown(p->c, QIO_CHANNEL_SHUTDOWN_BOTH, NULL);
         qemu_mutex_unlock(&p->mutex);
     }
 }
@@ -1176,7 +1175,6 @@ int multifd_load_cleanup(Error **errp)
         object_unref(OBJECT(p->c));
         p->c = NULL;
         qemu_mutex_destroy(&p->mutex);
-        qemu_sem_destroy(&p->sem);
         qemu_sem_destroy(&p->sem_sync);
         g_free(p->name);
         p->name = NULL;
@@ -1299,9 +1297,7 @@ int multifd_load_setup(void)
         MultiFDRecvParams *p = &multifd_recv_state->params[i];
 
         qemu_mutex_init(&p->mutex);
-        qemu_sem_init(&p->sem, 0);
         qemu_sem_init(&p->sem_sync, 0);
-        p->quit = false;
         p->id = i;
         p->pages = multifd_pages_init(page_count);
         p->packet_len = sizeof(MultiFDPacket_t)
-- 
2.17.1