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

[Jun'ichi Nomura]

On 11/04/11 18:19, Heiko Carstens 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().

struct pgpath is freed before dm_target when tearing down dm table.
So if the problematic completion was being done after freeing pgpath
but before freeing dm_target, crash would look like that
and what's happening seems the same for these dm crashes:
dm table was somehow destroyed while I/O was in-flight.

It's interesting that your test started to crash in dm with v3.0.7.
Have you gotten these dm crashes with v3.0.6 or before?
Have you hit the initially-reported scsi oops with v3.0.7?
Are your v3.0.6 and v3.0.7 compiled with same config and the tests
ran on same system?

> 
> 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.

-- 
Jun'ichi Nomura, NEC Corporation
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