Re: 2.6.23-mm1

Torsten Kaiser
2007-10-13T14:32:27Z

On 10/13/07, Jeff Garzik <jeff@garzik.org> wrote:
> Torsten Kaiser wrote:
> > On 10/13/07, Jeff Garzik <jeff@garzik.org> wrote:
> >> Torsten Kaiser wrote:
> > I can't follow you on SYNCHRONIZE CACHE.
> > The only command written to the syslog in the errors where
> > 0x60==ATA_CMD_FPDMA_READ and 0xB0 (which is not in
> > include/linux/ata.h, but ATA-6 says that this is SMART related. That
> > makes sense, as smartd is failing).
>
> In the traceback you have "ata_scsi_flush_xlat", which is the function
> that translates a SCSI sync-cache command into an ATA flush-cache command.

Aha. That makes sense.
But on the second error, where the drive was kicked out completely all
three traces did not have ata_scsi_flush_xlat.
First WARNING:
Oct 13 07:46:48 treogen [ 99.850000] Call Trace:
Oct 13 07:46:48 treogen [ 99.850000] [<ffffffff8044431a>]
ata_qc_issue+0x4aa/0x540
Oct 13 07:46:48 treogen [ 99.850000] [<ffffffff80432e60>] scsi_done+0x0/0x20
Oct 13 07:46:48 treogen [ 99.850000] [<ffffffff8044ce30>]
ata_scsi_pass_thru+0x0/0x2c0
Oct 13 07:46:48 treogen [ 99.850000] [<ffffffff8044a6ea>]
ata_scsi_translate+0xfa/0x180
Oct 13 07:46:48 treogen [ 99.850000] [<ffffffff80432e60>] scsi_done+0x0/0x20
...

Second+Third:
Oct 13 07:46:49 treogen [ 100.510000] [<ffffffff804442ef>]
ata_qc_issue+0x47f/0x540
Oct 13 07:46:49 treogen [ 100.510000] [<ffffffff80432e60>] scsi_done+0x0/0x20
Oct 13 07:46:49 treogen [ 100.510000] [<ffffffff80432e60>] scsi_done+0x0/0x20
Oct 13 07:46:49 treogen [ 100.510000] [<ffffffff8044a440>]
ata_scsi_rw_xlat+0x0/0x1b0
Oct 13 07:46:49 treogen [ 100.510000] [<ffffffff8044a6ea>]
ata_scsi_translate+0xfa/0x180
Oct 13 07:46:49 treogen [ 100.510000] [<ffffffff80432e60>] scsi_done+0x0/0x20
...

So the commands that generate the WARNINGs seem only later collateral damage.

> The "WARNING: at drivers/ata/libata-core.c:5752 ata_qc_issue()" also
> guides us to the code comment
>
> /* Make sure only one non-NCQ command is outstanding. The
> * check is skipped for old EH because it reuses active qc to
> * request ATAPI sense.
> */
>
> which is a check related to NCQ->off and off->NCQ edge cases.
>
> So those are the two bits of information I found interesting.

But I very much agree about this. But rather than 'normal' edges with
the cache flushes, I would blame it on the SMART commands from smartd
that trigger the switch.
Both errors happend during the startup of smartd.

> >> guess that sata_nv is not properly handling non-queued commands.
> >
> > But that still seems correct, as I would not expect that SMART
> > commands get queued. (Thats just a guess, as I did not try to find the
> > code that does this distinction)
> >
> >> This is a patch from libata-dev.git#nv-swncq (via #ALL).
> >
> > Comparing sata_nv.c from 2.6.23-rc8-mm1 and 2.6.23-mm1 I see two
> > changes, that look suspicious:
> >
> > http://git.kernel.org/?p=linux/kernel/git/jgarzik/libata-dev.git;a=commitdiff;h=31cc23b34913bc173680bdc87af79e551bf8cc0d
> >
> > The comment says: "ahci and sata_sil24 are converted to use ata_std_qc_defer()."
> > But the patch also adds ".qc_defer = ata_std_qc_defer," to sata_nv.c

Looking more at this patch, I thing the code change is correct and
only the comment is missing sata_nv. (Only ahci, sil24 and nv seem to
use NCQ und so need the logic from qc_defer)

> > The second change is the removal of the 'lock' spinlock from sata_nv.c
> > that was used in nv_swncq_qc_issue and nv_swncq_host_interrupt.
> >
> > Should I try to revert one or both of these changes?
>
> If you are git-capable, IMO the next steps in problem elimination should be

... I should really take the time install this, but I don't think git
will help in this special case, because:

> * download latest linux-2.6.git (currently
> 752097cec53eea111d087c545179b421e2bde98a)
> * build and test linux-2.6.git, to establish a new baseline

2.6.23-rc8-mm1 worked.

> * download latest libata-dev.git#nv-swncq (currently
> 3cb664c2d319a4fde5028c3c5dab6221fe70bd2d)

That commit (3cb664c2d319a4fde5028c3c5dab6221fe70bd2d) seems to be the
only commit relevant to swncq, as it adds it completely without any
partial steps that could be bisected.

> * build and test, with sata_nv module option swncq=0
> * build and test, with sata_nv module option swncq=1

I will try this. Currently I have sata_nv.swncq=1 in my kernel
commandline so its trivial to change that.
But as only 2 out of 3 boots failed, I think I hit another heisenbug.

> My gut feeling is that there is a lingering bug in sata_nv SWNCQ somewhere.

Older versions of SWNCQ already worked for me, so I don't think its a
general problem.
And as the symptoms would nicely fit into a race condition when
manipulating the NCQ state, the removal of the lock protecting the
private sata_nv defer_queue between 2.6.23-rc8-mm1 and 2.6.23-mm1
looks like the prime suspect.

So now booting with and without swncq and if swncq=0 works, I will try
to add the lock back...

Torsten