linux-kernel - Re: [ANNOUNCE] Status of unlocked

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Date:	Wed, 20 Oct 2010 17:30:31 -0700
From:	Giridhar Malavali <giridhar.malavali@...gic.com>
To:	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>
CC:	linux-kernel <linux-kernel@...r.kernel.org>,
	LinuxSCSI <linux-scsi@...r.kernel.org>,
	James Bottomley <James.Bottomley@...e.de>,
	Mike Christie <michaelc@...wisc.edu>,
	Andrew Vasquez <andrew.vasquez@...gic.com>
Subject: Re: [ANNOUNCE] Status of unlocked_qcmds=1 operation for .37




On 10/20/10 4:19 PM, "Nicholas A. Bellinger" <nab@...ux-iscsi.org> wrote:

> On Wed, 2010-10-20 at 15:37 -0700, Giridhar Malavali wrote:
>> 
>> 
> 
> <Trimming long CC'list>
> 
> Hi Giri,
> 
>> On 10/20/10 1:49 PM, "Nicholas A. Bellinger" <nab@...ux-iscsi.org> wrote:
>> 
>>> Greetings all,
>>> 
>>> So as we get closer to the .37 merge window, I wanted to take this
>>> oppourtunity to recap the current status of the drop-host_lock /
>>> unlocked_qcmds=1 patches, and what is required for the next RFCv5 and
>>> hopefully a merge into .37.  The last RFCv4 was posted here:
>>> 
>>> http://marc.info/?l=linux-kernel=128563953114561=2
>>> <http://marc.info/?l=linux-kernel=128563953114561=2
>>> <http://marc.info/?l=linux-kernel&m=128563953114561&w=2> >
>>> 
>>> Since then, Christof Schmitt has sent a patch to drop struct
>>> scsi_cmnd->serial_number usage in zfcp, and Tim Chen has sent an
>>> important fix to drop an extra host_lock access that I originally missed
>>> in qla2xxx SHT->queuecommand() that certainly would have deadlocked a
>>> running machine.   Many thanks to Christof and Tim for your
>>> contributions and review!
>>> 
>>> So at this point in the game the current score sits at:
>>> 
>>> *) core drivers/scsi remaining issue(s):
>>> 
>>> The issue raised by andmike during RFCv4 described as:
>>> 
>>> "If we skip __scsi_try_to_abort_cmd when REQ_ATOM_COMPLETE is set it
>>> would be correct for the scsi_decide_disposition cases but it would
>>> appear this would stop __scsi_try_to_abort_cmd from being called in the
>>> time out case as REQ_ATOM_COMPLETE is set prior to calling
>>> blk_rq_timed_out."
>>> 
>>> The complete discussion is here:
>>> 
>>> http://marc.info/?l=linux-scsi=128535319915212=2
>>> <http://marc.info/?l=linux-scsi=128535319915212=2
>>> <http://marc.info/?l=linux-scsi&m=128535319915212&w=2> >
>>> 
>>> We still need folks with experience to dig into this code, so you know
>>> the scsi_error.c code please jump in!
>>> 
>>> *) LLD libraries running by default w/ unlocked_qcmds=1
>>> 
>>> libiscsi: need ack from mnc
>>> libsas: need ack from jejb
>>> libfc: remaining rport state + host_lock less issue.  Need more input
>>>        from mnc for James Smart and Joe on this...
>>> libata: jgarzik thinks this should be OK, review and ack from tejun
>>>         would also be very helpful.
>>> 
>>> The main issue remaining here is the audit of libfc rport (and other..?)
>>> code that assumes host_lock is held to protect state.  mnc, do you have
>>> any more thoughts for James Smart and Joe here..?
>>> 
>>> *) Individual LLDs running by default w/ unlocked_qcmds=1
>>> 
>>> aic94xx: need ack maintainer at adaptec..?)
>>> mvsas: need ack maintainer at marvell..?)
>>> pm8001: need ack Jang Wang
>>> qla4xxx, qla2xxx: need ack Andrew Vasquez
>>> fnic:  need ack Joe Eykholt
>> 
>> The qla2xxx driver is modified not to depend on the host_lock and also to
>> drop usage of scsi_cmnd->serial_number. Both the patches are submitted to
>> linux-scsi and you can find more information at
>> 
>> http://marc.info/?l=linux-scsi=128716779923700=2
>> <http://marc.info/?l=linux-scsi&m=128716779923700&w=2>
> 
> Sure, but for the new fast unlocked_qcmds=1 operation in
> qla2xxx_queuecommand(), the host_lock access needs to be complete
> removed from SHT->queuecommand().   The above patch just moves the
> vha->host->host_lock unlock up in queuecommand(),  right..?
> 
> diff --git a/drivers/scsi/qla2xxx/qla_os.c b/drivers/scsi/qla2xxx/qla_os.c
> index b0c7139..77203b0 100644
> --- a/drivers/scsi/qla2xxx/qla_os.c
> +++ b/drivers/scsi/qla2xxx/qla_os.c
> @@ -545,6 +545,7 @@ qla2xxx_queuecommand(struct scsi_cmnd *cmd, void
> (*done)(struct scsi_cmnd *))
>         srb_t *sp;
>         int rval;
> 
> +       spin_unlock_irq(vha->host->host_lock);
>         if (ha->flags.eeh_busy) {
>                 if (ha->flags.pci_channel_io_perm_failure)
>                         cmd->result = DID_NO_CONNECT << 16;
> 
> <SNIP>
> 
> @@ -603,9 +599,11 @@ qc24_host_busy_lock:
>         return SCSI_MLQUEUE_HOST_BUSY;
> 
>  qc24_target_busy:
> +       spin_lock_irq(vha->host->host_lock);
>         return SCSI_MLQUEUE_TARGET_BUSY;
> 
>  qc24_fail_command:
> +       spin_lock_irq(vha->host->host_lock);
>         done(cmd);
> 
>         return 0;
> 
>> http://marc.info/?l=linux-scsi=128716779623683=2
>> <http://marc.info/?l=linux-scsi&m=128716779623683&w=2>
>> 
> 
> <nod> I had been only updating LLDs that actually used ->serial_number
> beyond a simple informational purposes for error recovery.  Thanks for
> removing this one preemptively!  8-)
> 
> Best,
> 
> --nab
> 

Hi Nicholas,

Yes, I understand. I was thinking that you are going to submit the patches
for all LLD with your final submission.

I will submit the patch which removes host_lock in queuecommand routine
completely then. 

-- Giri

> 
> 

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