Date:	Wed, 19 Nov 2008 18:29:19 +0100
From:	Jens Axboe <jens.axboe@...cle.com>
To:	"Miller, Mike (OS Dev)" <Mike.Miller@...com>
Cc:	Randy Dunlap <randy.dunlap@...cle.com>,
	scsi <linux-scsi@...r.kernel.org>,
	James Bottomley <James.Bottomley@...senpartnership.com>,
	lkml <linux-kernel@...r.kernel.org>,
	akpm <akpm@...ux-foundation.org>
Subject: Re: in 2.6.23-rc3-git7 in do_cciss_intr

On Wed, Nov 19 2008, Miller, Mike (OS Dev) wrote:
> 
> 
> > -----Original Message-----
> > From: Randy Dunlap [mailto:randy.dunlap@...cle.com]
> > Sent: Wednesday, November 19, 2008 11:23 AM
> > To: Miller, Mike (OS Dev)
> > Cc: Jens Axboe; scsi; James Bottomley; lkml; akpm
> > Subject: Re: in 2.6.23-rc3-git7 in do_cciss_intr
> >
> > Miller, Mike (OS Dev) wrote:
> > >
> > >> -----Original Message-----
> > >> From: Jens Axboe [mailto:jens.axboe@...cle.com]
> > >> Sent: Wednesday, November 19, 2008 2:52 AM
> > >> To: Randy Dunlap
> > >> Cc: scsi; Miller, Mike (OS Dev); James Bottomley; lkml; akpm
> > >> Subject: Re: in 2.6.23-rc3-git7 in do_cciss_intr
> > >>
> > >> On Tue, Nov 18 2008, Randy Dunlap wrote:
> > >>> Randy Dunlap wrote:
> > >>>> Randy Dunlap wrote:
> > >>>>> Miller, Mike (OS Dev) wrote:
> > >>>>>>> -----Original Message-----
> > >>>>>>> From: Randy Dunlap [mailto:randy.dunlap@...cle.com]
> > >>>>>>> Sent: Thursday, September 25, 2008 3:40 PM
> > >>>>>>> To: scsi
> > >>>>>>> Cc: Jens Axboe; Miller, Mike (OS Dev); James Bottomley; lkml;
> > >>>>>>> akpm
> > >>>>>>> Subject: Re: in 2.6.23-rc3-git7 in do_cciss_intr
> > >>>>>>>
> > >>>>>>> On Thu, 25 Sep 2008 13:33:07 -0700 Randy Dunlap wrote:
> > >>>>>>>
> > >>>>>>>> Jens Axboe wrote:
> > >>>>>>>>> On Thu, Sep 04 2008, Miller, Mike (OS Dev) wrote:
> > >>>>>>>>>>>>>> 0x3bb2 <do_cciss_intr+1649>:    mov    0x2(%r8),%dx
> > >>>>>>>>>>>>>> 0x3bb7 <do_cciss_intr+1654>:    test   %dx,%dx
> > >>>>>>>>>>>>>> 0x3bba <do_cciss_intr+1657>:    je     0x3f0e
> > >>>>>>> <do_cciss_intr+2509>
> > >>>>>>>>>>>>>> $ addr2line -e cciss.o -f  do_cciss_intr+0x627
> > >>>>>>>>>>>>>> SA5_fifo_full
> > >>>>>>>>>>>>>>
> > >> /home/rdunlap/linsrc/linux-2.6.27-rc3-git7/drivers/block/cciss.h:
> > >>>>>>> 2
> > >>>>>>>>>>> 06
> > >>>>>>>>>>>>> OK ...that's confusing.  It seems to be saying that
> > >>>>>>> ctrlr_info_t
> > >>>>>>>>>>>>> * was NULL.  However, I can't see a way of
> > >> getting into the
> > >>>>>>>>>>> fifo_full
> > >>>>>>>>>>>>> callback from do_cciss_intr ..
> > >>>>>>>>>>>>> especially not with an NULL host.
> > >>>>>>>>>>>>>
> > >>>>>>>>>>>>> James
> > >>>>>>>>>>>> That is weird. Even if we could get there
> > >> fifo_full doesn't
> > >>>>>>>>>>> do anything but wait for a bit.
> > >>>>>>>>>>>
> > >>>>>>>>>>> Hi,
> > >>>>>>>>>>>
> > >>>>>>>>>>> This just happened again.  This time it's on
> > >> 2.6.27-rc5-git3.
> > >>>>>>>>>>> ~Randy
> > >>>>>>>>>> Thanks Randy. I think. :)
> > >>>>>>>>>>
> > >>>>>>>>>> I'll try to recreate in my lab.
> > >>>>>>>>> This looks somewhat strange, mostly like 'c' is NULL
> > >> and it's
> > >>>>>>>>> oopsing in in removeQ (I don't think Randy's analysis is
> > >>>>>>> correct in
> > >>>>>>>>> assuming it's 'h' and it's in fifo_full). Given that 'c'
> > >>>>>>> cannot be
> > >>>>>>>>> NULL, it's c->prev or c->next that are NULL.
> > >>>>> This BUG: has happened (now) 5 times today.  Higher
> > >> frequency than
> > >>>>> usual for some reason.
> > >>>>>
> > >>>>> I enabled CCISS_DEBUG and added one printk in
> > removeQ().  On the
> > >>>>> first call
> > >>>> s/first/second/
> > >>>>
> > >>>>
> > >>>>> to removeQ(), both c->next and c->prev are NULL.
> > >>>>>
> > >>>>> Here's the kernel log output from cciss:
> > >>> I added a printk() in addQ() as well.  Here's the new output:
> > >>>
> > >>> HP CISS Driver (v 3.6.20)
> > >>> ACPI: PCI Interrupt Link [LNKA] enabled at IRQ 54 cciss
> > >> 0000:42:08.0:
> > >>> PCI INT A -> Link[LNKA] -> GSI 54 (level, high) -> IRQ 54
> > command =
> > >>> 147 irq = 36 board_id = 3211103c cciss 0000:42:08.0: irq 87 for
> > >>> MSI/MSI-X address 0 = fdf80000 cfg base address = 10 cfg
> > >> base address
> > >>> index = 0 cfg offset = 400 Controller Configuration information
> > >>> ------------------------------------
> > >>>    Signature = CISS
> > >>>    Spec Number = 1
> > >>>    Transport methods supported = 0x6
> > >>>    Transport methods active = 0x3
> > >>>    Requested transport Method = 0x0
> > >>>    Coalesce Interrupt Delay = 0x0
> > >>>    Coalesce Interrupt Count = 0x1
> > >>>    Max outstanding commands = 0x256
> > >>>    Bus Types = 0x200000
> > >>>    Server Name =
> > >>>    Heartbeat Counter = 0x1672
> > >>>
> > >>>
> > >>> Trying to put board into Simple mode I counter got to 1 0
> > Controller
> > >>> Configuration information
> > >>> ------------------------------------
> > >>>    Signature = CISS
> > >>>    Spec Number = 1
> > >>>    Transport methods supported = 0x6
> > >>>    Transport methods active = 0x3
> > >>>    Requested transport Method = 0x0
> > >>>    Coalesce Interrupt Delay = 0x0
> > >>>    Coalesce Interrupt Count = 0x1
> > >>>    Max outstanding commands = 0x256
> > >>>    Bus Types = 0x200000
> > >>>    Server Name =
> > >>>    Heartbeat Counter = 0x1672
> > >>>
> > >>>
> > >>> cciss0: <0x3238> at PCI 0000:42:08.0 IRQ 87 using DAC
> > >>> cciss: intr_pending 8
> > >>> cciss: addQ: Qptr=ffff88027e0100b8, c=ffff88007f83e000
> > >>> cciss: removeQ: Qptr=ffff88027e0100b8, c=ffff88007f83e000,
> > >>> next=ffff88007f83e000, prev=ffff88007f83e000 Sending
> > >> 7f83e000 - down
> > >>> to controller
> > >>> cciss: addQ: Qptr=ffff88027e0100c0, c=ffff88007f83e000
> > >>> cciss: intr_pending 8
> > >>> cciss:  Read 4 back from board
> > >>> cciss: removeQ: Qptr=ffff88027e0100c0, c=ffff88007f840000,
> > >>> next=0000000000000000, prev=0000000000000000
> > >>> BUG: unable to handle kernel NULL pointer dereference at
> > >>> 0000000000000248
> > >> Randy, can you post the debug patch you used? The above goes boom
> > >> when it attempts to remove a command that isn't on the
> > list, the Qptr
> > >> in the last example should be empty, hence the oops. So I'd be
> > >> interested in seeing what removeQ() calls this is, I'm
> > assuming it's
> > >> this bit in
> > >> do_cciss_intr():
> > >>
> > >>       ...
> > >>               while (c->busaddr != a) {
> > >>                        c = c->next;
> > >>                        if (c == h->cmpQ)
> > >>                                break;
> > >>                }
> > >>        }
> > >>        /*
> > >>         * If we've found the command, take it off the
> > >>         * completion Q and free it
> > >>         */
> > >>        if (c->busaddr == a) {
> > >>                removeQ(&h->cmpQ, c);
> > >>                if (c->cmd_type == CMD_RWREQ) {
> > >>                        complete_command(h, c, 0);
> > >>                         ...
> > >>
> > >> If so, what part of the c lookup are you hitting - the on
> > that does:
> > >>
> > >>         c = h->cmd_pool + a2;
> > >>
> > >> or the c->busaddr check that his shown above?
> > >>
> > >> --
> > > Randy,
> > > I still can't reproduce this bug. I have your config file
> > on a BL465c w/e200i. Just to confirm, you only see this at
> > init time, correct?
> >
> > Yes, only at init time.
> >
> > > Please post your debug patch as Jens requested.
> >
> > Done (separately).
> >
> > I need to back up a bit.  Yesterday these BUGs happened
> > consistenly, so I wondered why.  Then I recalled that for
> > debugging another bug/problem, I had changed the test
> > system's normal boot kernel from 2.6.25 to 2.6.18-8.  The
> > test system is used to build and then boot the new kernel
> > *via kexec*, so it's quite possible (or certain) that
> > something in the kexec world has been fixed since 2.6.18.  I
> > don't recall seeing this problem lately when using 2.6.25 to
> > kexec/boot the new test kernel, so I'm quite willing to drop
> > the bug for now and then re-open it if I see the problem again.  OK??
> 
> Ahhhh, the kexec piece was missing. Now I don't feel quite so
> clueless. I'm OK with dropping the bug for now. Jens, James?

Yeah, kexec is definitely a clue. My guess is that we got some sort of
left over completion. Regardless of the status of this particular bug or
not, I think it would be a good idea to add some checks for when a
command is attempted removed from a queue it isn't currently on.

-- 
Jens Axboe

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