Date: Tue, 4 Jun 2024 09:32:38 +0800
From: Changhui Zhong <czhong@...hat.com>
To: Li Nan <linan666@...weicloud.com>
Cc: Ming Lei <ming.lei@...hat.com>, axboe@...nel.dk, ZiyangZhang@...ux.alibaba.com, 
	linux-block@...r.kernel.org, linux-kernel@...r.kernel.org, yukuai3@...wei.com, 
	yi.zhang@...wei.com, houtao1@...wei.com, yangerkun@...wei.com
Subject: Re: [PATCH] ublk_drv: fix NULL pointer dereference in ublk_ctrl_start_recovery()

On Mon, Jun 3, 2024 at 10:20 AM Li Nan <linan666@...weicloud.com> wrote:
>
>
>
> 在 2024/6/3 8:39, Ming Lei 写道:
>
> [...]
>
> >> diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
> >> index 4e159948c912..99b621b2d40f 100644
> >> --- a/drivers/block/ublk_drv.c
> >> +++ b/drivers/block/ublk_drv.c
> >> @@ -2630,7 +2630,8 @@ static void ublk_queue_reinit(struct ublk_device *ub, struct ublk_queue *ubq)
> >>   {
> >>      int i;
> >>
> >> -    WARN_ON_ONCE(!(ubq->ubq_daemon && ubq_daemon_is_dying(ubq)));
> >> +    if (WARN_ON_ONCE(!(ubq->ubq_daemon && ubq_daemon_is_dying(ubq))))
> >> +            return;
> >
> > Yeah, it is one bug. However, it could be addressed by adding the check in
> > ublk_ctrl_start_recovery() and return immediately in case of NULL ubq->ubq_daemon,
> > what do you think about this way?
> >
>
> Check ub->nr_queues_ready seems better. How about:
>
> @@ -2662,6 +2662,8 @@ static int ublk_ctrl_start_recovery(struct
> ublk_device *ub,
>          mutex_lock(&ub->mutex);
>          if (!ublk_can_use_recovery(ub))
>                  goto out_unlock;
> +       if (!ub->nr_queues_ready)
> +               goto out_unlock;
>          /*
>           * START_RECOVERY is only allowd after:
>           *
>
> >
> > Thanks,
> > Ming
>
> --
> Thanks,
> Nan
>


Hi,Nan

After applying your new patch, I did not trigger "NULL pointer
dereference" and "Warning",
but hit task hung "Call Trace" info, please check

[13617.812306] running generic/004
[13622.293674] blk_print_req_error: 91 callbacks suppressed
[13622.293681] I/O error, dev ublkb4, sector 233256 op 0x1:(WRITE)
flags 0x8800 phys_seg 1 prio class 0
[13622.308145] I/O error, dev ublkb4, sector 233256 op 0x0:(READ)
flags 0x0 phys_seg 2 prio class 0
[13622.316923] I/O error, dev ublkb4, sector 233264 op 0x1:(WRITE)
flags 0x8800 phys_seg 1 prio class 0
[13622.326048] I/O error, dev ublkb4, sector 233272 op 0x0:(READ)
flags 0x0 phys_seg 1 prio class 0
[13622.334828] I/O error, dev ublkb4, sector 233272 op 0x1:(WRITE)
flags 0x8800 phys_seg 1 prio class 0
[13622.343954] I/O error, dev ublkb4, sector 233312 op 0x0:(READ)
flags 0x0 phys_seg 1 prio class 0
[13622.352733] I/O error, dev ublkb4, sector 233008 op 0x0:(READ)
flags 0x0 phys_seg 1 prio class 0
[13622.361514] I/O error, dev ublkb4, sector 233112 op 0x0:(READ)
flags 0x0 phys_seg 1 prio class 0
[13622.370292] I/O error, dev ublkb4, sector 233192 op 0x1:(WRITE)
flags 0x8800 phys_seg 1 prio class 0
[13622.379419] I/O error, dev ublkb4, sector 233120 op 0x0:(READ)
flags 0x0 phys_seg 1 prio class 0
[13641.069695] INFO: task fio:174413 blocked for more than 122 seconds.
[13641.076061]       Not tainted 6.10.0-rc1+ #1
[13641.080338] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs"
disables this message.
[13641.088164] task:fio             state:D stack:0     pid:174413
tgid:174413 ppid:174386 flags:0x00004002
[13641.088168] Call Trace:
[13641.088170]  <TASK>
[13641.088171]  __schedule+0x221/0x670
[13641.088177]  schedule+0x23/0xa0
[13641.088179]  io_schedule+0x42/0x70
[13641.088181]  blk_mq_get_tag+0x118/0x2b0
[13641.088185]  ? gup_fast_pgd_range+0x280/0x370
[13641.088188]  ? __pfx_autoremove_wake_function+0x10/0x10
[13641.088192]  __blk_mq_alloc_requests+0x194/0x3a0
[13641.088194]  blk_mq_submit_bio+0x241/0x6c0
[13641.088196]  __submit_bio+0x8a/0x1f0
[13641.088199]  submit_bio_noacct_nocheck+0x168/0x250
[13641.088201]  ? submit_bio_noacct+0x45/0x560
[13641.088203]  __blkdev_direct_IO_async+0x167/0x1a0
[13641.088206]  blkdev_write_iter+0x1c8/0x270
[13641.088208]  aio_write+0x11c/0x240
[13641.088212]  ? __rq_qos_issue+0x21/0x40
[13641.088214]  ? blk_mq_start_request+0x34/0x1a0
[13641.088216]  ? io_submit_one+0x68/0x380
[13641.088218]  ? kmem_cache_alloc_noprof+0x4e/0x320
[13641.088221]  ? fget+0x7c/0xc0
[13641.088224]  ? io_submit_one+0xde/0x380
[13641.088226]  io_submit_one+0xde/0x380
[13641.088228]  __x64_sys_io_submit+0x80/0x160
[13641.088229]  do_syscall_64+0x79/0x150
[13641.088233]  ? syscall_exit_to_user_mode+0x6c/0x1f0
[13641.088237]  ? do_io_getevents+0x8b/0xe0
[13641.088238]  ? syscall_exit_work+0xf3/0x120
[13641.088241]  ? syscall_exit_to_user_mode+0x6c/0x1f0
[13641.088243]  ? do_syscall_64+0x85/0x150
[13641.088245]  ? do_syscall_64+0x85/0x150
[13641.088247]  ? blk_mq_flush_plug_list.part.0+0x108/0x160
[13641.088249]  ? rseq_get_rseq_cs+0x1d/0x220
[13641.088252]  ? rseq_ip_fixup+0x6d/0x1d0
[13641.088254]  ? blk_finish_plug+0x24/0x40
[13641.088256]  ? syscall_exit_to_user_mode+0x6c/0x1f0
[13641.088258]  ? do_syscall_64+0x85/0x150
[13641.088260]  ? syscall_exit_to_user_mode+0x6c/0x1f0
[13641.088262]  ? do_syscall_64+0x85/0x150
[13641.088264]  ? syscall_exit_to_user_mode+0x6c/0x1f0
[13641.088266]  ? do_syscall_64+0x85/0x150
[13641.088268]  ? do_syscall_64+0x85/0x150
[13641.088270]  ? do_syscall_64+0x85/0x150
[13641.088272]  ? clear_bhb_loop+0x45/0xa0
[13641.088275]  ? clear_bhb_loop+0x45/0xa0
[13641.088277]  ? clear_bhb_loop+0x45/0xa0
[13641.088279]  entry_SYSCALL_64_after_hwframe+0x76/0x7e
[13641.088281] RIP: 0033:0x7ff92150713d
[13641.088283] RSP: 002b:00007ffca1ef81f8 EFLAGS: 00000246 ORIG_RAX:
00000000000000d1
[13641.088285] RAX: ffffffffffffffda RBX: 00007ff9217e2f70 RCX: 00007ff92150713d
[13641.088286] RDX: 000055863b694fe0 RSI: 0000000000000010 RDI: 00007ff92164d000
[13641.088287] RBP: 00007ff92164d000 R08: 00007ff91936d000 R09: 0000000000000180
[13641.088288] R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000010
[13641.088289] R13: 0000000000000000 R14: 000055863b694fe0 R15: 000055863b6970c0
[13641.088291]  </TASK>

Thanks，
Changhui

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