On 11/04/11 22:30, Mike Snitzer wrote:
> On Fri, Nov 04 2011 at 5:19am -0400,
> Heiko Carstens <heiko.carstens@xxxxxxxxxx> wrote:
>
>> On Thu, Nov 03, 2011 at 02:25:48PM -0400, Mike Snitzer wrote:
>>> On Mon, Oct 31 2011 at 9:00am -0400,
>>> Heiko Carstens <heiko.carstens@xxxxxxxxxx> wrote:
>>>
>>>> On Mon, Oct 31, 2011 at 08:46:06PM +0900, Jun'ichi Nomura wrote:
>>>>> Hm, dm_softirq_done is generic completion code of original
>>>>> request in dm-multipath.
>>>>> So oops here might be another manifestation of use-after-free.
>>>>>
>>>>> Do you always hit the oops at the same address?
>>>>
>>>> I think we saw this bug the first time. But before that the scsi
>>>> logging level was higher. Gonzalo is trying to recreate it with
>>>> the same (old) scsi logging level.
>>>> Afterwards we will try with barrier=0.
>>>>
>>>> Both on v3.0.7 btw.
>>>>
>>>>> Could you find corresponding source code line for
>>>>> the crashed address, dm_softirq_done+0x72/0x140,
>>>>> and which pointer was invalid?
>>>>
>>>> It crashes in the inlined function dm_done() when trying to
>>>> dereference tio (aka clone->end_io_data):
>>>>
>>>> static void dm_done(struct request *clone, int error, bool mapped)
>>>> {
>>>> int r = error;
>>>> struct dm_rq_target_io *tio = clone->end_io_data;
>>>> dm_request_endio_fn rq_end_io = tio->ti->type->rq_end_io;
>>>
>>> Hi,
>>>
>>> Which underlying storage driver is being used by this multipath device?
>>
>> It's the s390 only zfcp device driver.
>>
>> FWIW, yet another use-after-free crash, this time however in multipath_end_io:
>>
>> [96875.870593] Unable to handle kernel pointer dereference at virtual kernel address 6b6b6b6b6b6b6000
>> [96875.870602] Oops: 0038 [#1]
>> [96875.870674] PREEMPT SMP DEBUG_PAGEALLOC
>> [96875.870683] Modules linked in: dm_round_robin sunrpc ipv6 qeth_l2 binfmt_misc dm_multipath scsi_dh dm_mod qeth ccwgroup [la\
>> st unloaded: scsi_wait_scan]
>> [96875.870722] CPU: 2 Tainted: G W 3.0.7-50.x.20111024-s390xdefault #1
>> [96875.870728] Process udevd (pid: 36697, task: 0000000072c8a3a8, ksp: 0000000057c43868)
>> [96875.870732] Krnl PSW : 0704200180000000 000003e001347138 (multipath_end_io+0x50/0x140 [dm_multipath])
>> [96875.870746] R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:0 AS:0 CC:2 PM:0 EA:3
>> [96875.870751] Krnl GPRS: 0000000000000000 000003e000000000 6b6b6b6b6b6b6b6b 00000000717ab940
>> [96875.870755] 0000000000000000 00000000717abab0 0000000000000002 0700000000000008
>> [96875.870759] 0000000000000002 0000000000000000 0000000058dd37a8 000000006f845478
>> [96875.870764] 000003e0012e1000 000000005613d1f0 000000007a737bf0 000000007a737ba0
>> [96875.870768] Krnl Code: 000003e00134712a: b90200dd ltgr %r13,%r13
>> [96875.870793] 000003e00134712e: a7840017 brc 8,3e00134715c
>> [96875.870800] 000003e001347132: e320d0100004 lg %r2,16(%r13)
>> [96875.870809] >000003e001347138: e31020180004 lg %r1,24(%r2)
>> [96875.870818] 000003e00134713e: e31010580004 lg %r1,88(%r1)
>> [96875.870827] 000003e001347144: b9020011 ltgr %r1,%r1
>> [96875.870835] 000003e001347148: a784000a brc 8,3e00134715c
>> [96875.870841] 000003e00134714c: 41202018 la %r2,24(%r2)
>> [96875.870889] Call Trace:
>> [96875.870892] ([<0700000000000008>] 0x700000000000008)
>> [96875.870897] [<000003e0012e3662>] dm_softirq_done+0x9a/0x140 [dm_mod]
>> [96875.870915] [<000000000040d29c>] blk_done_softirq+0xd4/0xf0
>> [96875.870925] [<00000000001587c2>] __do_softirq+0xda/0x398
>> [96875.870932] [<000000000010f47e>] do_softirq+0xe2/0xe8
>> [96875.870940] [<0000000000158e2c>] irq_exit+0xc8/0xcc
>> [96875.870945] [<00000000004ceb48>] do_IRQ+0x910/0x1bfc
>> [96875.870953] [<000000000061a164>] io_return+0x0/0x16
>> [96875.870961] [<000000000019c84e>] lock_acquire+0xd2/0x204
>> [96875.870969] ([<000000000019c836>] lock_acquire+0xba/0x204)
>> [96875.870974] [<0000000000615f8e>] mutex_lock_killable_nested+0x92/0x520
>> [96875.870983] [<0000000000292796>] vfs_readdir+0x8a/0xe4
>> [96875.870992] [<00000000002928e0>] SyS_getdents+0x60/0xe8
>> [96875.870999] [<0000000000619af2>] sysc_noemu+0x16/0x1c
>> [96875.871024] [<000003fffd1ec83e>] 0x3fffd1ec83e
>> [96875.871028] INFO: lockdep is turned off.
>> [96875.871031] Last Breaking-Event-Address:
>> [96875.871037] [<000003e0012e3660>] dm_softirq_done+0x98/0x140 [dm_mod]
>>
>> static int multipath_end_io(struct dm_target *ti, struct request *clone,
>> int error, union map_info *map_context)
>> {
>> struct multipath *m = ti->private;
>> struct dm_mpath_io *mpio = map_context->ptr;
>> struct pgpath *pgpath = mpio->pgpath;
>> struct path_selector *ps;
>> int r;
>>
>> r = do_end_io(m, clone, error, mpio);
>> if (pgpath) {
>> ps = &pgpath->pg->ps; <--- crashes here
>> if (ps->type->end_io)
>> ps->type->end_io(ps, &pgpath->path, mpio->nr_bytes);
>> }
>> mempool_free(mpio, m->mpio_pool);
>>
>> return r;
>> }
>>
>> It crashes when trying to derefence pgpath, which was freed. Since we have
>> SLUB debugging turned on the freed object tells us that it was allocated
>> via a call to multipath_ctr() and freed via a call to free_priority_group().
>>
>> FWIW, this reproduction was done with barriers off.
>>
>> Btw, since I cc'ed you rather late I'm not sure if you are aware of the
>> test scenario: it's I/O stress with multipathing were paths come and go
>> all the time. It usually takes quite a few hours before the crashes are
>> observed.
>
> OK, thanks for the backstory.
>
> That is the same type of testing we've been doing with some partners
> for RHEL6.2 with the qla2xxx driver. They have seen the same crash that
> you originally reported here: https://lkml.org/lkml/2011/10/31/64
>
> The really interesting observation that was made is that the qla2xxx
> driver was made lockless in RHEL6.2. We've found that reverting the
> qla2xxx lockless changes eliminates the problems seen with it and I/O
> stress testing with multipath path failures.
It's interesting.
Have you analyzed how the lockless change caused the dm crash?
> The zfcp driver was also made lockless upstream, via this commit:
> e55f875 [SCSI] zfcp: Issue FCP command without holding SCSI host_lock
>
> It would be great if you could try reverting e55f875 and see how your
> testing goes.
>
> If doing so resolves the crashes for you then the post mortem on why
> these lockless SCSI driver changes are causing such odd multipath
> completion failures is going to be "fun" ;)
--
Jun'ichi Nomura, NEC Corporation
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