Messages in this thread | | | Subject | Re: [PATCH 2/2] target: Fix target_wait_for_sess_cmds breakage with active signals | From | "Nicholas A. Bellinger" <> | Date | Wed, 10 Oct 2018 22:56:05 -0700 |
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Hello MNC & Co,
On Wed, 2018-10-10 at 11:58 -0500, Mike Christie wrote: > On 10/09/2018 10:23 PM, Nicholas A. Bellinger wrote: > > From: Nicholas Bellinger <nab@linux-iscsi.org> > > > > With the addition of commit 00d909a107 in v4.19-rc, it incorrectly assumes no > > signals will be pending for task_struct executing the normal session shutdown > > and I/O quiesce code-path. > >
<SNIP>
> > diff --git a/drivers/target/target_core_transport.c b/drivers/target/target_core_transport.c > > index 86c0156..fc3093d2 100644 > > --- a/drivers/target/target_core_transport.c > > +++ b/drivers/target/target_core_transport.c > > @@ -2754,7 +2754,7 @@ static void target_release_cmd_kref(struct kref *kref) > > if (se_sess) { > > spin_lock_irqsave(&se_sess->sess_cmd_lock, flags); > > list_del_init(&se_cmd->se_cmd_list); > > - if (list_empty(&se_sess->sess_cmd_list)) > > + if (se_sess->sess_tearing_down && list_empty(&se_sess->sess_cmd_list)) > > I think there is another issue with 00d909a107 and ibmvscsi_tgt. > > The problem is that ibmvscsi_tgt never called > target_sess_cmd_list_set_waiting. It only called > target_wait_for_sess_cmds. So before 00d909a107 there was a bug in that > driver and target_wait_for_sess_cmds never did what was intended because > sess_wait_list would always be empty. > > With 00d909a107, we no longer need to call > target_sess_cmd_list_set_waiting to wait for outstanding commands, so > for ibmvscsi_tgt will now wait for commands like we wanted. However, the > commit added a WARN_ON that is hit if target_sess_cmd_list_set_waiting > is not called, so we could hit that. > > So I think we need to add a target_sess_cmd_list_set_waiting call in > ibmvscsi_tgt to go along with your patch chunk above and make sure we do > not trigger the WARN_ON. >
Nice catch. :)
With target_wait_for_sess_cmd() usage pre 00d909a107 doing a list-splice in target_sess_cmd_list_set_waiting(), this particular usage in ibmvscsi_tgt has always been list_empty(&sess->sess_wait_list) = true (eg: no se_cmd I/O is quiesced, because no se_cmd in sess_wait_list) since commit 712db3eb in 4.9.y code.
That said, ibmvscsi_tgt usage is very similar to vhost/scsi in the respect individual /sys/kernel/config/target/$FABRIC/$WWN/$TPGT/ endpoints used by VMs do not remove their I_T nexus while the VM is active.
So AFAICT, ibmvscsi_tgt doesn't strictly need target_sess_wait_for_cmd() at all if this is true.
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