Re: [GIT PULL] Queue free fix (was Re: [PATCH] block: Free queue resources at blk_release_queue())

[James Bottomley <James.Bottomley@HansenPartnership.com>]

On Mon, 2011-10-31 at 11:05 +0100, Heiko Carstens wrote:
> On Tue, Oct 18, 2011 at 11:29:40AM -0500, James Bottomley wrote:
> > On Tue, 2011-10-18 at 17:45 +0200, Heiko Carstens wrote:
> > > On Tue, Oct 18, 2011 at 10:31:20PM +0900, Jun'ichi Nomura wrote:
> > > > On 10/17/11 23:06, James Bottomley wrote:
> > > > > On Mon, 2011-10-17 at 17:46 +0900, Jun'ichi Nomura wrote:
> > > > >> On 10/15/11 01:03, James Bottomley wrote:
> > > > >>> On Thu, 2011-10-13 at 15:09 +0200, Steffen Maier wrote:
> > > > >>>> Initially, we encountered use-after-free bugs in
> > > > >>>> scsi_print_command / scsi_dispatch_cmd
> > > > >>>> http://marc.info/?l=linux-scsi&m=130824013229933&w=2
> > > > >>
> > > > >> It is interesting that both this and the older report
> > > > >> got oopsed in scsi_log_send(), while there are other
> > > > >> dereferences of 'cmd' around scsi_dispatch_cmd().
> > > > >> Are there any reason they are special? Just by accident?
> > > > > 
> > > > > Right, that's why it looks like the command area got freed rather than
> > > > > the command pointer was bogus (6b is a poison free pattern).  Perhaps if
> > > > > the reporter could pin down the failing source line, we'd know better
> > > > > what was going on?
> > > > 
> > > > Yeah, that might be useful.
> > > 
> > > The struct scsi_cmnd that was passed to scsi_log_send() was already freed
> > > (contents completely 6b6b6b...).
> > > Since SLUB debugging was turned on we can see that it was freed from
> > > __scsi_put_command(). Not too much of a surprise.
> > 
> > But it does tell us the put must be racing with dispatch, since
> > dereferencing the command to find the device worked higher up in
> > scsi_dispatch_cmd().
> > 
> > There is one way to invalidate the theory that we cloned something with
> > an attached command, and that's to put 
> > 
> > BUG_ON(rq->special)
> > 
> > in blk_insert_cloned_request().  I think we're careful about clearing
> > it, so it should work (perhaps a warn on just in case).
> 
> It _looks_ like we do not hit the BUG_ON() that. This time we get this instead:
> 
> [ 4024.937870] Unable to handle kernel pointer dereference at virtual kernel address 000003e004d41000
> [ 4024.937886] Oops: 0011 [#1] PREEMPT SMP DEBUG_PAGEALLOC
> [ 4024.937899] Modules linked in: dm_round_robin sunrpc ipv6 qeth_l2 binfmt_misc dm_multipath scsi_dh dm_mod qeth ccwgroup [las
> t unloaded: scsi_wait_scan]
> [ 4024.937925] CPU: 1 Not tainted 3.0.7-50.x.20111021-s390xdefault #1
> [ 4024.937930] Process ksoftirqd/1 (pid: 1942, task: 0000000079c6c750, ksp: 0000000073adfc50)
> [ 4024.937936] Krnl PSW : 0704000180000000 000003e00126263a (dm_softirq_done+0x72/0x140 [dm_mod])
> [ 4024.937959]            R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:0 AS:0 CC:0 PM:0 EA:3
> [ 4024.937966] Krnl GPRS: 000000007b9156b0 000003e004d41100 000000000e14b600 000000000000006d
> [ 4024.937971]            00000000715332b0 000000000c140ce8 000000000090d2ef 0000000000000005
> [ 4024.937977]            0000000000000001 0000000000000101 000000000c140d00 0000000000000000
> [ 4024.937983]            000003e001260000 000003e00126f098 0000000073adfd08 0000000073adfcb8
> [ 4024.938001] Krnl Code: 000003e00126262a: f0a0000407f1        srp     4(11,%r0),2033,0
> [ 4024.938009]            000003e001262630: e31050080004        lg      %r1,8(%r5)
> [ 4024.938017]            000003e001262636: 58b05180            l       %r11,384(%r5)
> [ 4024.938024]           >000003e00126263a: e31010080004        lg      %r1,8(%r1)
> [ 4024.938031]            000003e001262640: e31010500004        lg      %r1,80(%r1)
> [ 4024.938038]            000003e001262646: b9020011            ltgr    %r1,%r1
> [ 4024.938045]            000003e00126264a: a784ffdf            brc     8,3e001262608
> [ 4024.938053]            000003e00126264e: e32050080004        lg      %r2,8(%r5)
> [ 4024.938060] Call Trace:
> [ 4024.938063] ([<070000000040716c>] 0x70000000040716c)
> [ 4024.938069]  [<000000000040d29c>] blk_done_softirq+0xd4/0xf0
> [ 4024.938080]  [<00000000001587c2>] __do_softirq+0xda/0x398
> [ 4024.938088]  [<0000000000158ba0>] run_ksoftirqd+0x120/0x23c
> [ 4024.938095]  [<000000000017c2aa>] kthread+0xa6/0xb0
> [ 4024.938102]  [<000000000061970e>] kernel_thread_starter+0x6/0xc
> [ 4024.938112]  [<0000000000619708>] kernel_thread_starter+0x0/0xc
> [ 4024.938118] INFO: lockdep is turned off.
> [ 4024.938121] Last Breaking-Event-Address:
> [ 4024.938124]  [<000003e001262600>] dm_softirq_done+0x38/0x140 [dm_mod]
> [ 4024.938135]  
> [ 4024.938139] Kernel panic - not syncing: Fatal exception in interrupt
> [ 4024.938144] CPU: 1 Tainted: G      D     3.0.7-50.x.20111021-s390xdefault #1
> [ 4024.938150] Process ksoftirqd/1 (pid: 1942, task: 0000000079c6c750, ksp: 0000000073adfc50)
> [ 4024.938155] 0000000073adf958 0000000073adf8d8 0000000000000002 0000000000000000 
> [ 4024.938164]        0000000073adf978 0000000073adf8f0 0000000073adf8f0 000000000061386a 
> [ 4024.938174]        0000000000000000 0000000000000000 0000000000000005 0000000000100ec6 
> [ 4024.938184]        000000000000000d 000000000000000c 0000000073adf940 0000000000000000 
> [ 4024.938194]        0000000000000000 0000000000100a18 0000000073adf8d8 0000000073adf918 
> [ 4024.938205] Call Trace:
> [ 4024.938208] ([<0000000000100926>] show_trace+0xee/0x144)
> [ 4024.938216]  [<0000000000613694>] panic+0xb0/0x234
> [ 4024.938224]  [<0000000000100ec6>] die+0x15a/0x168
> [ 4024.938230]  [<000000000011fb9e>] do_no_context+0xba/0xf8
> [ 4024.938306]  [<000000000061c074>] do_dat_exception+0x378/0x3e4
> [ 4024.938314]  [<0000000000619e02>] pgm_exit+0x0/0x4
> [ 4024.938319]  [<000003e00126263a>] dm_softirq_done+0x72/0x140 [dm_mod]
> [ 4024.938329] ([<070000000040716c>] 0x70000000040716c)
> [ 4024.938334]  [<000000000040d29c>] blk_done_softirq+0xd4/0xf0
> [ 4024.938341]  [<00000000001587c2>] __do_softirq+0xda/0x398
> [ 4024.938347]  [<0000000000158ba0>] run_ksoftirqd+0x120/0x23c
> [ 4024.938354]  [<000000000017c2aa>] kthread+0xa6/0xb0
> [ 4024.938360]  [<000000000061970e>] kernel_thread_starter+0x6/0xc
> [ 4024.938366]  [<0000000000619708>] kernel_thread_starter+0x0/0xc
> [ 4024.938373] INFO: lockdep is turned off.
> 
> So we thought we might as well upgrade to 3.1 but immediately got a
> 
> kernel BUG at block/blk-flush.c:323!
> 
> which was handled here https://lkml.org/lkml/2011/10/4/105 and
> here https://lkml.org/lkml/2011/10/12/408 .
> 
> But no patches for that one went upstream AFAICS.

Well, all I can say is "hm".  You put only a BUG_ON() in the code, which
wasn't triggered, but now we get a completely different oops.  However,
I think it does point to the dm barrier handling code.  Can you turn off
barriers and see if all oopses go away?

James