From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:40681) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fVaVk-0003Iu-RB for qemu-devel@nongnu.org; Wed, 20 Jun 2018 06:38:51 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fVaVh-0000CS-G8 for qemu-devel@nongnu.org; Wed, 20 Jun 2018 06:38:48 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:57656 helo=mx1.redhat.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1fVaVh-0000CD-Aj for qemu-devel@nongnu.org; Wed, 20 Jun 2018 06:38:45 -0400 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id D29C27721C for ; Wed, 20 Jun 2018 10:38:44 +0000 (UTC) Date: Wed, 20 Jun 2018 11:38:41 +0100 From: "Dr. David Alan Gilbert" Message-ID: <20180620103841.GH2549@work-vm> References: <20180523111817.1463-1-quintela@redhat.com> <20180523111817.1463-12-quintela@redhat.com> <20180611164516.GI2661@work-vm> <87d0wlyle1.fsf@secure.mitica> <20180620090127.GB2549@work-vm> <87r2l1lrp0.fsf@secure.mitica> <20180620094626.GD2549@work-vm> <87in6dlreq.fsf@secure.mitica> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87in6dlreq.fsf@secure.mitica> Subject: Re: [Qemu-devel] [PATCH v13 11/12] migration: Remove not needed semaphore and quit List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Juan Quintela Cc: qemu-devel@nongnu.org, lvivier@redhat.com, peterx@redhat.com * Juan Quintela (quintela@redhat.com) wrote: > "Dr. David Alan Gilbert" wrote: > > * Juan Quintela (quintela@redhat.com) wrote: > >> "Dr. David Alan Gilbert" wrote: > >> > * Juan Quintela (quintela@redhat.com) wrote: > >> >> "Dr. David Alan Gilbert" 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 > 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 > -- > 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); OK, so with any luck all the threads now exit; do we still have a close/unref once we're sure they have all exited? Dave > 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 > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK