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Subject: Re: [PATCH V4] brd: check and limit max_part par
To:     Zhiqiang Liu <liuzhiqiang26@huawei.com>,
        Ming Lei <ming.lei@redhat.com>, Jens Axboe <axboe@kernel.dk>
Cc:     linux-block@vger.kernel.org,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Mingfangsen <mingfangsen@huawei.com>, Guiyao <guiyao@huawei.com>,
        wubo40@huawei.comwubo, Louhongxiang <louhongxiang@huawei.com>
References: <76ad8074-c2ba-4bb3-3e8b-3a4925999964@huawei.com>
 <fe925c14-fe70-b237-b793-e6b865687c11@huawei.com>
From:   Bob Liu <bob.liu@oracle.com>
Message-ID: <606d4b34-7f2f-2207-a725-2999b75cbbb7@oracle.com>
Date:   Mon, 3 Feb 2020 20:36:37 +0800
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On 2/3/20 9:53 AM, Zhiqiang Liu wrote:
> Friendly ping...
> 
> On 2020/1/21 12:04, 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.
>>
>> --
>> 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>
>> ---
>>  drivers/block/brd.c | 27 +++++++++++++++++++++++----
>>  1 file changed, 23 insertions(+), 4 deletions(-)
>>

Looks good to me.
Reviewed-by: Bob Liu <bob.liu@oracle.com>

>> diff --git a/drivers/block/brd.c b/drivers/block/brd.c
>> index df8103dd40ac..4684f95e3369 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;
>>  	disk->fops		= &brd_fops;
>>  	disk->private_data	= brd;
>>  	disk->queue		= brd->brd_queue;
>> @@ -468,6 +469,25 @@ static struct kobject *brd_probe(dev_t dev, int *part, void *data)
>>  	return kobj;
>>  }
>>
>> +static inline void brd_check_and_reset_par(void)
>> +{
>> +	if (unlikely(!max_part))
>> +		max_part = 1;
>> +
>> +	if (max_part > DISK_MAX_PARTS) {
>> +		pr_info("brd: max_part can't be larger than %d, reset max_part = %d.\n",
>> +			DISK_MAX_PARTS, DISK_MAX_PARTS);
>> +		max_part = DISK_MAX_PARTS;
>> +	}
>> +
>> +	/*
>> +	 * make sure 'max_part' can be divided exactly by (1U << MINORBITS),
>> +	 * otherwise, it is possiable to get same dev_t when adding partitions.
>> +	 */
>> +	if ((1U << MINORBITS) % max_part != 0)
>> +		max_part = 1UL << fls(max_part);
>> +}
>> +
>>  static int __init brd_init(void)
>>  {
>>  	struct brd_device *brd, *next;
>> @@ -491,8 +511,7 @@ static int __init brd_init(void)
>>  	if (register_blkdev(RAMDISK_MAJOR, "ramdisk"))
>>  		return -EIO;
>>
>> -	if (unlikely(!max_part))
>> -		max_part = 1;
>> +	brd_check_and_reset_par();
>>
>>  	for (i = 0; i < rd_nr; i++) {
>>  		brd = brd_alloc(i);
>>
>