[dm-devel] [PATCH 1/3] dm: don't grab target io reference in dm_zone_map_bio
Damien Le Moal
damien.lemoal at opensource.wdc.com
Mon Apr 11 03:10:35 UTC 2022
On 4/11/22 11:55, Damien Le Moal wrote:
> On 4/11/22 11:19, Damien Le Moal wrote:
>> On 4/11/22 10:04, Ming Lei wrote:
>>> On Mon, Apr 11, 2022 at 09:50:57AM +0900, Damien Le Moal wrote:
>>>> On 4/11/22 09:36, Ming Lei wrote:
>>>>> On Mon, Apr 11, 2022 at 09:18:56AM +0900, Damien Le Moal wrote:
>>>>>> On 4/9/22 02:12, Ming Lei wrote:
>>>>>>> dm_zone_map_bio() is only called from __map_bio in which the io's
>>>>>>> reference is grabbed already, and the reference won't be released
>>>>>>> until the bio is submitted, so no necessary to do it dm_zone_map_bio
>>>>>>> any more.
>>>>>>
>>>>>> I do not think that this patch is correct. Removing the extra reference on
>>>>>> the io can lead to problems if the io is completed in the target
>>>>>> ->map(ti, clone) call or before dm_zone_map_bio_end() is called for the
>>>>>> DM_MAPIO_SUBMITTED or DM_MAPIO_REMAPPED cases. dm_zone_map_bio_end() needs
>>>>>
>>>>> __map_bio():
>>>>> ...
>>>>> dm_io_inc_pending(io);
>>>>> ...
>>>>> dm_zone_map_bio(tio);
>>>>> ...
>>>>
>>>> dm-crypt (for instance) may terminate the clone bio immediately in its
>>>> ->map() function context, resulting in the bio_endio()clone) ->
>>>> clone_endio() -> dm_io_dec_pending() call chain.
>>>>
>>>> With that, the io is gone and dm_zone_map_bio_end() will not have a valid
>>>> reference on the orig bio.
>>>
>>> Any target can complete io during ->map. Here looks nothing is special with
>>> dm-crypt or dm-zone, why does only dm zone need extra reference?
>>>
>>> The reference counter is initialized as 1 in init_clone_info(), dm_io_inc_pending()
>>> in __map_bio() increases it to 2, so after the above call chain you mentioned is done,
>>> the counter becomes 1. The original bio can't be completed until dm_io_dec_pending()
>>> in dm_split_and_process_bio() is called.
>>>
>>> Or maybe I miss any extra requirement from dm-zone?
>>
>> Something is wrong... With and without your patch, when I setup a dm-crypt
>> target on top of a zoned nullblk device, I get:
>>
>> [ 292.596454] device-mapper: uevent: version 1.0.3
>> [ 292.602746] device-mapper: ioctl: 4.46.0-ioctl (2022-02-22)
>> initialised: dm-devel at redhat.com
>> [ 292.732217] general protection fault, probably for non-canonical
>> address 0xdffffc0000000002: 0000 [#1] PREEMPT SMP KASAN PTI
>> [ 292.743724] KASAN: null-ptr-deref in range
>> [0x0000000000000010-0x0000000000000017]
>> [ 292.751409] CPU: 0 PID: 4259 Comm: systemd-udevd Not tainted
>> 5.18.0-rc2+ #1458
>> [ 292.758746] Hardware name: Supermicro Super Server/X11DPL-i, BIOS 3.3
>> 02/21/2020
>> [ 292.766250] RIP: 0010:dm_zone_map_bio+0x146/0x1740 [dm_mod]
>> [ 292.771938] Code: 00 00 4d 8b 65 10 48 8d 43 28 48 89 44 24 10 49 8d 44
>> 24 10 48 89 c2 48 89 44 24 18 48 b8 00 00 00 00 00 fc ff df 48 c1 ea 03
>> <0f> b6 04 02 84 c0 74 08 3c 03 0f 8e 78 0e 00 00 45 8b 7c 24 10 41
>> [ 292.790946] RSP: 0018:ffff8883cd847218 EFLAGS: 00010202
>> [ 292.796260] RAX: dffffc0000000000 RBX: ffff8885c5bcdce8 RCX:
>> 1ffff11034470027
>> [ 292.803496] RDX: 0000000000000002 RSI: 0000000000000008 RDI:
>> ffff8885c5bcdc60
>> [ 292.810732] RBP: 1ffff11079b08e4f R08: ffff8881a23801d8 R09:
>> ffff8881a238013f
>> [ 292.817970] R10: ffff88821c594040 R11: 0000000000000001 R12:
>> 0000000000000000
>> [ 292.825206] R13: ffff8885c5bcdc50 R14: ffff8881a2380000 R15:
>> ffff8885c5bcdd08
>> [ 292.832442] FS: 00007fe169b06b40(0000) GS:ffff88880fc00000(0000)
>> knlGS:0000000000000000
>> [ 292.840646] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> [ 292.846481] CR2: 00007ffd80a57a38 CR3: 00000004b91b0006 CR4:
>> 00000000007706f0
>> [ 292.853722] DR0: 0000000000000000 DR1: 0000000000000000 DR2:
>> 0000000000000000
>> [ 292.860957] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7:
>> 0000000000000400
>> [ 292.868194] PKRU: 55555554
>> [ 292.870949] Call Trace:
>> [ 292.873446] <TASK>
>> [ 292.875593] ? lock_is_held_type+0xd7/0x130
>> [ 292.879860] ? dm_set_zones_restrictions+0x8f0/0x8f0 [dm_mod]
>> [ 292.885718] ? __module_address.part.0+0x25/0x300
>> [ 292.890509] ? is_module_address+0x43/0x70
>> [ 292.894674] ? static_obj+0x8a/0xc0
>> [ 292.898233] __map_bio+0x352/0x740 [dm_mod]
>> [ 292.902512] dm_submit_bio+0x72f/0x17a0 [dm_mod]
>> [ 292.907222] ? find_held_lock+0x2c/0x110
>> [ 292.911217] ? __send_empty_flush+0x2b0/0x2b0 [dm_mod]
>> [ 292.916459] ? lock_release+0x3b2/0x6f0
>> [ 292.920368] ? lock_downgrade+0x6d0/0x6d0
>> [ 292.924458] ? lock_is_held_type+0xd7/0x130
>> [ 292.928714] __submit_bio+0x12a/0x1f0
>> [ 292.932450] submit_bio_noacct_nocheck+0x324/0x840
>> [ 292.937324] ? should_fail_request+0x70/0x70
>> [ 292.941670] ? rcu_read_lock_sched_held+0x3f/0x70
>> [ 292.946458] ? submit_bio_noacct+0xfa4/0x1530
>> [ 292.950888] ? lock_is_held_type+0xd7/0x130
>> [ 292.957813] mpage_readahead+0x32e/0x4b0
>> [ 292.964470] ? do_mpage_readpage+0x17c0/0x17c0
>> [ 292.971661] ? blkdev_write_begin+0x20/0x20
>> [ 292.978567] ? lock_release+0x3b2/0x6f0
>> [ 292.985073] ? folio_add_lru+0x217/0x3f0
>> [ 292.991620] ? lock_downgrade+0x6d0/0x6d0
>> [ 292.998237] read_pages+0x18c/0x990
>> [ 293.004308] ? memcg_list_lru_alloc+0x810/0x810
>> [ 293.011404] ? folio_add_lru+0x238/0x3f0
>> [ 293.017805] ? file_ra_state_init+0xd0/0xd0
>> [ 293.024395] ? policy_node+0xbb/0x140
>> [ 293.030416] page_cache_ra_unbounded+0x258/0x410
>> [ 293.037376] force_page_cache_ra+0x281/0x400
>> [ 293.043944] filemap_get_pages+0x25e/0x1290
>> [ 293.050342] ? __lock_acquire+0x1603/0x6180
>> [ 293.056654] ? filemap_add_folio+0x140/0x140
>> [ 293.063002] ? lock_is_held_type+0xd7/0x130
>> [ 293.069236] filemap_read+0x29e/0x910
>> [ 293.074927] ? filemap_get_pages+0x1290/0x1290
>> [ 293.081378] ? __lock_acquire+0x1603/0x6180
>> [ 293.087558] blkdev_read_iter+0x20c/0x640
>> [ 293.093529] ? cp_new_stat+0x47a/0x590
>> [ 293.099190] ? cp_old_stat+0x470/0x470
>> [ 293.104795] new_sync_read+0x2e4/0x520
>> [ 293.110362] ? __x64_sys_lseek+0x1d0/0x1d0
>> [ 293.116269] ? lock_acquire+0x1b2/0x4d0
>> [ 293.121928] ? find_held_lock+0x2c/0x110
>> [ 293.127648] vfs_read+0x312/0x430
>> [ 293.132755] ksys_read+0xf3/0x1d0
>> [ 293.137863] ? __x64_sys_pwrite64+0x1f0/0x1f0
>> [ 293.144032] do_syscall_64+0x35/0x80
>> [ 293.149391] entry_SYSCALL_64_after_hwframe+0x44/0xae
>>
>> The crash is at: drivers/md/dm-zone.c:499, which is
>> dm_need_zone_wp_tracking() called from dm_zone_map_bio(). The orig_bio
>> pointer is invalid. Weird. Investigating.
>>
>> Also checking why our weekly test runs did not catch this.
>
> This fixes the issue:
>
> diff --git a/drivers/md/dm.c b/drivers/md/dm.c
> index 3c5fad7c4ee6..3dd6735450c5 100644
> --- a/drivers/md/dm.c
> +++ b/drivers/md/dm.c
> @@ -581,7 +581,7 @@ static struct dm_io *alloc_io(struct mapped_device
> *md, struct bio *bio)
> io->status = 0;
> atomic_set(&io->io_count, 1);
> this_cpu_inc(*md->pending_io);
> - io->orig_bio = NULL;
> + io->orig_bio = bio;
> io->md = md;
> io->map_task = current;
> spin_lock_init(&io->lock);
>
> Otherwise, the dm-zone.c code sees a NULL orig_bio.
> However, this change may be messing up the bio accounting. Need to check that.
Forgot to mention that with the above fix + your patch applied, everything
seems to be fine. No issues. The extra reference is indeed not needed.
Only the orig_bio initialization missing is a problem.
--
Damien Le Moal
Western Digital Research
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