[Bug 118081] open-iscsi Ping timeout erro

[bugzilla-daemon@bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=118081

--- Comment #3 from nab <nab@linux-iscsi.org> ---
Hey Mike & Co,

Apologies for missing this bug-report.  Comments below.

(Adding target-devel CC')

On Fri, 2016-05-13 at 11:19 -0500, Mike Christie wrote:
> On 05/11/2016 10:34 PM, bugzilla-daemon@bugzilla.kernel.org wrote:
> > https://bugzilla.kernel.org/show_bug.cgi?id=118081
> > 
> >             Bug ID: 118081
> >            Summary: open-iscsi Ping timeout erro
> >            Product: SCSI Drivers
> >            Version: 2.5
> >     Kernel Version: 4.4.7
> >           Hardware: All
> >                 OS: Linux
> >               Tree: Mainline
> >             Status: NEW
> >           Severity: normal
> >           Priority: P1
> >          Component: Other
> >           Assignee: scsi_drivers-other@kernel-bugs.osdl.org
> >           Reporter: liuzhengyuang521@gmail.com
> >         Regression: No
> > 
> > Hi everyone:
> > I create a target using fileio as the backend storage on ARM64 server. The
> > initiator reported some errors showed bellow  while perform iozone test.
> > 
> > [178444.145679]  connection14:0: ping timeout of 5 secs expired, recv timeout
> > 5, last rx 4339462894, last ping 4339464146, now 4339465400
> > [178444.145706]  connection14:0: detected conn error (1011)
> > [178469.674313]  connection14:0: detected conn error (1020)
> > [178504.420979]  connection14:0: ping timeout of 5 secs expired, recv timeout
> > 5, last rx 4339477953, last ping 4339479204, now 4339480456
> > [178504.421001]  connection14:0: detected conn error (1011)
> > [178532.064262]  connection14:0: detected conn error (1020)
> > [178564.584087]  connection14:0: ping timeout of 5 secs expired, recv timeout
> > 5, last rx 4339492980, last ping 4339494232, now 4339495484
> > ..............................
> > 
> > I try to trace the function call of target iscsi. Then, I found the  receiving 
> > thread of target iscsi blocked at fd_execute_sync_cache -> vfs_fsync_range.
> > Further, vfs_fsync_range may takes more than 10 seconds to return,while
> > initiator Ping timeout would happened after 5 seconds.   vfs_fsync_range was
> > call with the form vfs_fsync_range(fd_dev->fd_file, 0, LLONG_MAX, 1) every
> > times  which means sync all device cache. 
> > So, is this a bug?
> > How  does Initiator send sync_cache scsi command? 
> > Does it need to sync all device cache at once?
> > Any reply would be thankful.
> > 
> 
> The upper layers like the FS or application determine when to send a
> sync cache. They send down a request and the iscsi layer just sends it
> to the target.
> 
> You are using LIO right? It looks like we end up syncing the entire
> device sometimes. I think for iscsi pings/Nops that have the immediate
> bit set, the target would want to reply to them right away. They should
> not be getting stuck behind these type of commands.
> 
> Nick, what do you think?
> 

In modern iscsi-target code, the backend sbc_ops->execute_sync_cache()
call is invoked directly from iscsi_trx kthread process context.

For FILEIO backends, this can block immediate iscsi commands like NOPs
on the same connection (eg: socket) processing a SYNCHRONIZE_CACHE CDB
that is taking a long time to complete.

Wrt to Liu's follow-up question, an initiator should attempt to retry
all outstanding commands that did not receive a response once the
initiator side NopOut timeout has fired.

So from an application perspective, the initiator NopOut timeout and
subsequent iscsi session reinstatement should not be propagating up a
SYNCHRONIZE_CACHE failure unless the default 120 second Linux/iSCSI
initiator I/O timeout has elapsed.

Liu, are you seeing something different wrt iozone on a Linux host..?

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