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Date:   Tue, 4 Feb 2020 16:52:18 +0800
From:   Ming Lei <ming.lei@redhat.com>
To:     Zhiqiang Liu <liuzhiqiang26@huawei.com>
Cc:     Jens Axboe <axboe@kernel.dk>, linux-block@vger.kernel.org,
        linux-kernel@vger.kernel.org, Mingfangsen <mingfangsen@huawei.com>,
        "wubo (T)" <wubo40@huawei.com>, Guiyao <guiyao@huawei.com>,
        Yanxiaodan <yanxiaodan@huawei.com>
Subject: Re: [PATCH V5] brd: check and limit max_part par
Message-ID: <20200204085218.GA19922@ming.t460p>
References: <3f053491-d8c1-7092-58d1-85afaa2e68df@huawei.com>
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On Tue, Feb 04, 2020 at 10:44:18AM +0800, Zhiqiang Liu wrote:
> 
> In brd_init func, rd_nr num of brd_device are firstly allocated
> and add in brd_devices, then brd_devices are traversed to add each
> brd_device by calling add_disk func. When allocating brd_device,
> the disk->first_minor is set to i * max_part, if rd_nr * max_part
> is larger than MINORMASK, two different brd_device may have the same
> devt, then only one of them can be successfully added.
> when rmmod brd.ko, it will cause oops when calling brd_exit.
> 
> Follow those steps:
>   # modprobe brd rd_nr=3 rd_size=102400 max_part=1048576
>   # rmmod brd
> then, the oops will appear.
> 
> Oops log:
> [  726.613722] Call trace:
> [  726.614175]  kernfs_find_ns+0x24/0x130
> [  726.614852]  kernfs_find_and_get_ns+0x44/0x68
> [  726.615749]  sysfs_remove_group+0x38/0xb0
> [  726.616520]  blk_trace_remove_sysfs+0x1c/0x28
> [  726.617320]  blk_unregister_queue+0x98/0x100
> [  726.618105]  del_gendisk+0x144/0x2b8
> [  726.618759]  brd_exit+0x68/0x560 [brd]
> [  726.619501]  __arm64_sys_delete_module+0x19c/0x2a0
> [  726.620384]  el0_svc_common+0x78/0x130
> [  726.621057]  el0_svc_handler+0x38/0x78
> [  726.621738]  el0_svc+0x8/0xc
> [  726.622259] Code: aa0203f6 aa0103f7 aa1e03e0 d503201f (7940e260)
> 
> Here, we add brd_check_and_reset_par func to check and limit max_part par.
> 
> --
> V4->V5:(suggested by Ming Lei)
>  - make sure max_part is not larger than DISK_MAX_PARTS
> 
> V3->V4:(suggested by Ming Lei)
>  - remove useless change
>  - add one limit of max_part
> 
> V2->V3: (suggested by Ming Lei)
>  - clear .minors when running out of consecutive minor space in brd_alloc
>  - remove limit of rd_nr
> 
> V1->V2:
>  - add more checks in brd_check_par_valid as suggested by Ming Lei.
> 
> Signed-off-by: Zhiqiang Liu <liuzhiqiang26@huawei.com>
> Reviewed-by: Bob Liu <bob.liu@oracle.com>
> ---
>  drivers/block/brd.c | 27 +++++++++++++++++++++++----
>  1 file changed, 23 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/block/brd.c b/drivers/block/brd.c
> index df8103dd40ac..6b9db3f63cb7 100644
> --- a/drivers/block/brd.c
> +++ b/drivers/block/brd.c
> @@ -389,11 +389,12 @@ static struct brd_device *brd_alloc(int i)
>  	 *  is harmless)
>  	 */
>  	blk_queue_physical_block_size(brd->brd_queue, PAGE_SIZE);
> -	disk = brd->brd_disk = alloc_disk(max_part);
> +	disk = brd->brd_disk = alloc_disk(((i * max_part) & ~MINORMASK) ?
> +			0 : max_part);
>  	if (!disk)
>  		goto out_free_queue;
>  	disk->major		= RAMDISK_MAJOR;
> -	disk->first_minor	= i * max_part;
> +	disk->first_minor	= i * disk->minors;

As I told you, the above change isn't needed, otherwise:

Reviewed-by: Ming Lei <ming.lei@redhat.com>


Thanks, 
Ming