Re: [PATCH] block/loop: fix race between I/O and set_status

[Jiri Slaby]

On 02/11/2017, 04:40 AM, Ming Lei wrote:
> Inside set_status, transfer need to setup again, so
> we have to drain IO before the transition, otherwise
> oops may be triggered like the following:
> 
> 	divide error: 0000 [#1] SMP KASAN
> 	CPU: 0 PID: 2935 Comm: loop7 Not tainted 4.10.0-rc7+ #213
> 	Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs
> 	01/01/2011
> 	task: ffff88006ba1e840 task.stack: ffff880067338000
> 	RIP: 0010:transfer_xor+0x1d1/0x440 drivers/block/loop.c:110
> 	RSP: 0018:ffff88006733f108 EFLAGS: 00010246
> 	RAX: 0000000000000000 RBX: ffff8800688d7000 RCX: 0000000000000059
> 	RDX: 0000000000000000 RSI: 1ffff1000d743f43 RDI: ffff880068891c08
> 	RBP: ffff88006733f160 R08: ffff8800688d7001 R09: 0000000000000000
> 	R10: 0000000000000000 R11: 0000000000000000 R12: ffff8800688d7000
> 	R13: ffff880067b7d000 R14: dffffc0000000000 R15: 0000000000000000
> 	FS:  0000000000000000(0000) GS:ffff88006d000000(0000)
> 	knlGS:0000000000000000
> 	CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> 	CR2: 00000000006c17e0 CR3: 0000000066e3b000 CR4: 00000000001406f0
> 	Call Trace:
> 	 lo_do_transfer drivers/block/loop.c:251 [inline]
> 	 lo_read_transfer drivers/block/loop.c:392 [inline]
> 	 do_req_filebacked drivers/block/loop.c:541 [inline]
> 	 loop_handle_cmd drivers/block/loop.c:1677 [inline]
> 	 loop_queue_work+0xda0/0x49b0 drivers/block/loop.c:1689
> 	 kthread_worker_fn+0x4c3/0xa30 kernel/kthread.c:630
> 	 kthread+0x326/0x3f0 kernel/kthread.c:227
> 	 ret_from_fork+0x31/0x40 arch/x86/entry/entry_64.S:430
> 	Code: 03 83 e2 07 41 29 df 42 0f b6 04 30 4d 8d 44 24 01 38 d0 7f 08
> 	84 c0 0f 85 62 02 00 00 44 89 f8 41 0f b6 48 ff 25 ff 01 00 00 99 <f7>
> 	7d c8 48 63 d2 48 03 55 d0 48 89 d0 48 89 d7 48 c1 e8 03 83
> 	RIP: transfer_xor+0x1d1/0x440 drivers/block/loop.c:110 RSP:
> 	ffff88006733f108
> 	---[ end trace 0166f7bd3b0c0933 ]---
> 
> Reported-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Ming Lei <tom.leiming@xxxxxxxxx>
> ---
>  drivers/block/loop.c | 17 ++++++++++++-----
>  1 file changed, 12 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/block/loop.c b/drivers/block/loop.c
> index ed5259510857..4b52a1690329 100644
> --- a/drivers/block/loop.c
> +++ b/drivers/block/loop.c
> @@ -1097,9 +1097,12 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
>  	if ((unsigned int) info->lo_encrypt_key_size > LO_KEY_SIZE)
>  		return -EINVAL;
>  
> +	/* I/O need to be drained during transfer transition */
> +	blk_mq_freeze_queue(lo->lo_queue);
> +
>  	err = loop_release_xfer(lo);
>  	if (err)
> -		return err;
> +		goto exit;
>  
>  	if (info->lo_encrypt_type) {
>  		unsigned int type = info->lo_encrypt_type;
> @@ -1114,12 +1117,14 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info)

I might be missing context, but given this is not explained in the log,
I must ask why are not these returns also converted?

        if (info->lo_encrypt_type) {
                unsigned int type = info->lo_encrypt_type;

                if (type >= MAX_LO_CRYPT)
                        return -EINVAL;
                xfer = xfer_funcs[type];
                if (xfer == NULL)
                        return -EINVAL;
        } else
                xfer = NULL;

>  
>  	err = loop_init_xfer(lo, xfer, info);
>  	if (err)
> -		return err;
> +		goto exit;
>  
>  	if (lo->lo_offset != info->lo_offset ||
>  	    lo->lo_sizelimit != info->lo_sizelimit)
> -		if (figure_loop_size(lo, info->lo_offset, info->lo_sizelimit))
> -			return -EFBIG;
> +		if (figure_loop_size(lo, info->lo_offset, info->lo_sizelimit)) {
> +			err = -EFBIG;
> +			goto exit;
> +		}
>  
>  	loop_config_discard(lo);
>  
> @@ -1156,7 +1161,9 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
>  	/* update dio if lo_offset or transfer is changed */
>  	__loop_update_dio(lo, lo->use_dio);
>  
> -	return 0;
> + exit:
> +	blk_mq_unfreeze_queue(lo->lo_queue);
> +	return err;
>  }
>  
>  static int
> 

thanks,
-- 
js
suse labs