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

From: Heiko Carstens
Date: Fri Nov 04 2011 - 05:19:43 EST

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.
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