Date:	Mon, 16 Jul 2007 22:14:49 +0200
From:	Ian Kumlien <pomac@...or.com>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	Chuck Ebbert <cebbert@...hat.com>, Linux-kernel@...r.kernel.org,
	Nick Piggin <npiggin@...e.de>
Subject: Re: [BUG] AS io-scheduler.

On mån, 2007-07-16 at 21:56 +0200, Jens Axboe wrote:
> On Mon, Jul 16 2007, Ian Kumlien wrote:
> > On mån, 2007-07-16 at 19:29 +0200, Jens Axboe wrote:
> > > On Mon, Jul 16 2007, Chuck Ebbert wrote:
> > > > On 07/15/2007 11:20 AM, Ian Kumlien wrote:
> > > > > I had emerge --sync failing several times... 
> > > > > 
> > > > > So i checked dmesg and found some info, attached further down.
> > > > > This is a old VIA C3 machine with one disk, it's been running most
> > > > > kernels in the 2.6.x series with no problems until now.
> > > > > 
> > > > > PS. Don't forget to CC me
> > > > > DS.
> > > > > 
> > > > > BUG: unable to handle kernel paging request at virtual address ea86ac54
> > > > >  printing eip:
> > > > > c022dfec
> > > > > *pde = 00000000
> > > > > Oops: 0000 [#1]
> > > > > Modules linked in: eeprom i2c_viapro vt8231 i2c_isa skge
> > > > > CPU:    0
> > > > > EIP:    0060:[<c022dfec>]    Not tainted VLI
> > > > > EFLAGS: 00010082   (2.6.22.1 #26)
> > > > > EIP is at as_can_break_anticipation+0xc/0x190
> > > > > eax: dfcdaba0   ebx: dfcdaba0   ecx: 0035ff95   edx: cb296844
> > > > > esi: cb296844   edi: dfcdaba0   ebp: 00000000   esp: ceff6a70
> > > > > ds: 007b   es: 007b   fs: 0000  gs: 0033  ss: 0068
> > > > > Process rsync (pid: 1667, ti=ceff6000 task=d59cf5b0 task.ti=ceff6000)
> > > > > Stack: cb296844 00000001 cb296844 dfcdaba0 00000000 c022efc8 cb296844
> > > > > 00000000 
> > > > >        dfcffb9c c0227a76 dfcffb9c 00000000 c016e96e cb296844 00000000
> > > > > dfcffb9c 
> > > > >        00000000 c022af64 00000000 dfcffb9c 00000008 00000000 08ff6b30
> > > > > c04d1ec0 
> > > > > Call Trace:
> > > > >  [<c022efc8>] as_add_request+0xa8/0xc0
> > > > >  [<c0227a76>] elv_insert+0xa6/0x150
> > > > >  [<c016e96e>] bio_phys_segments+0xe/0x20
> > > > >  [<c022af64>] __make_request+0x384/0x490
> > > > >  [<c02add1e>] ide_do_request+0x6ee/0x890
> > > > >  [<c02294ab>] generic_make_request+0x18b/0x1c0
> > > > >  [<c022b596>] submit_bio+0xa6/0xb0
> > > > >  [<c013b7b8>] mempool_alloc+0x28/0xa0
> > > > >  [<c016bb66>] __find_get_block+0xf6/0x130
> > > > >  [<c016e0bc>] bio_alloc_bioset+0x8c/0xf0
> > > > >  [<c016b647>] submit_bh+0xb7/0xe0
> > > > >  [<c016c1f8>] ll_rw_block+0x78/0x90
> > > > >  [<c019c85d>] search_by_key+0xdd/0xd20
> > > > >  [<c016c201>] ll_rw_block+0x81/0x90
> > > > >  [<c011f190>] irq_exit+0x40/0x60
> > > > >  [<c01066e4>] do_IRQ+0x94/0xb0
> > > > >  [<c0104bc3>] common_interrupt+0x23/0x30
> > > > >  [<c018beca>] reiserfs_read_locked_inode+0x6a/0x490
> > > > >  [<c018e580>] reiserfs_find_actor+0x0/0x20
> > > > >  [<c018c33b>] reiserfs_iget+0x4b/0x80
> > > > >  [<c018e570>] reiserfs_init_locked_inode+0x0/0x10
> > > > >  [<c0189824>] reiserfs_lookup+0xa4/0xf0
> > > > >  [<c0157b03>] do_lookup+0xa3/0x140
> > > > >  [<c0159265>] __link_path_walk+0x615/0xa20
> > > > >  [<c0168a18>] __mark_inode_dirty+0x28/0x150
> > > > >  [<c01631c1>] mntput_no_expire+0x11/0x50
> > > > >  [<c01596b2>] link_path_walk+0x42/0xb0
> > > > >  [<c0159960>] do_path_lookup+0x130/0x150
> > > > >  [<c015a190>] __user_walk_fd+0x30/0x50
> > > > >  [<c0154766>] vfs_lstat_fd+0x16/0x40
> > > > >  [<c01547df>] sys_lstat64+0xf/0x30
> > > > >  [<c0103c42>] syscall_call+0x7/0xb
> > > > >  =======================
> > > > 
> > > > static int as_can_break_anticipation(struct as_data *ad, struct request *rq)
> > > > {
> > > >         struct io_context *ioc;
> > > >         struct as_io_context *aic;
> > > > 
> > > >         ioc = ad->io_context;  <======== ad is bogus
> > > >         BUG_ON(!ioc);
> > > > 
> > > > 
> > > > Call chain is:
> > > > 
> > > > 	as_add_request
> > > > 	as_update_rq:
> > > > 	        if (ad->antic_status == ANTIC_WAIT_REQ
> > > >         	                || ad->antic_status == ANTIC_WAIT_NEXT) {
> > > >                 	if (as_can_break_anticipation(ad, rq))
> > > >                         	as_antic_stop(ad);
> > > >         	}
> > > > 
> > > > 
> > > > So somehow 'ad' became invalid between the time ad->antic_status was
> > > > checked and as_can_break_anticipation() tried to access ad->io_context?
> > > 
> > > That's impossible, ad is persistent unless the io scheduler is attempted
> > > removed. Did you fiddle with switching io schedulers while this
> > > happened? If not, then something corrupted your memory. And I'm not
> > > aware of any io scheduler switching bugs, so the oops would still be
> > > highly suspect if so.
> > 
> > I wasn't fiddling with the scheduler, it's quite happily been running AS
> > for quite some time.
> 
> OK, that rules that out then. Then your oops looks very much like
> hardware trouble. Perhaps a border liner PSU? Just an idea.

It uses a laptop psu, that doesn't need cooling, this is a microitx
board =)

> > Actually it ran AS for the entire 2.6.21 and 2.6.20 life cycles.
> 
> There's essentially only one change in AS between 2.6.21 and 2.6.22, and
> that is converting a jiffes vs msec error. So no real code change.

Hummm, odd... 

> > > You write emerge - are you using an experimental compiler? Or did you
> > > recently change hardware? Is it warmer than usual?
> > 
> > No change in hardware, no change in compiler either.
> > 
> > gcc (GCC) 4.1.2 (Gentoo 4.1.2)
> > 
> > Which is the same compiler that compiled 2.6.21 afair.
> > 
> > It's been more humid, but not warmer... Were talking about a cpu that
> > usually idles at 17 deg =)
> 
> Probably not the heat, then.

Currenlty:
CPU Temp:  +25.6°C

This is all passively cooled btw, it was lower a while ago, bit the
webserver is still loaded.

> > There might however have been more io load, right now it's 220
> > connections to my webserver and it's 5 days since my friend released the
> > mix they are downloading.
> > 
> > (I'm preparing to switch it all over to a core2duo with mirrored disks,
> > which is a wee bit more suited to this kind of load)
> > 
> > Sent data: 8062.27 Mb (4620.55 kbit/s)
> > Requests: 56284 (235/min)
> > 
> > Webserver uptime 9h
> 
> My gut says that this is the hardware falling over, for whatever reason.
> Since it's otherwise stable, it could be something marginal pushing it
> over. Like your higher load (be it CPU, or disk).

It's only ever happened once.
(But it blocked any and all rsyncs... Common io worked)

This kinds of loads happens now and then, first it's slashdot finding
the icculus.org mirror of postal2 (long time ago, i know) and then it's
someone releasing a new mix... I always find out by noticing the amount
of webconnections increase.

> You could try and boot with the noop IO scheduler and see if it still
> oopses. Not sure would else to suggest, your box will likely pass
> memtest just fine.

It's currently running with cfq since ~2 days without a problem.

I really can't take it down and do a memtest on it, it's my mailserver,
webserver, firewall etc etc =)

Just let me know what kind of information you might want and i'll put it
all up... =)

-- 
Ian Kumlien <pomac () vapor ! com> -- http://pomac.netswarm.net

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