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Subject: Re: md/dm-mpath: check whether all pgpaths have same uuid in
 multipath_ctr()
To:     Mike Snitzer <snitzer@redhat.com>,
        Christoph Hellwig <hch@infradead.org>
CC:     <agk@redhat.com>, <dm-devel@redhat.com>,
        "jejb@linux.ibm.com" <jejb@linux.ibm.com>,
        "martin.petersen@oracle.com" <martin.petersen@oracle.com>,
        <linux-kernel@vger.kernel.org>, <linux-scsi@vger.kernel.org>,
        linfeilong <linfeilong@huawei.com>,
        lixiaokeng <lixiaokeng@huawei.com>,
        "wubo (T)" <wubo40@huawei.com>
References: <c8f86351-3036-0945-90d2-2e020d68ccf2@huawei.com>
 <20210322081155.GE1946905@infradead.org> <20210322142207.GB30698@redhat.com>
From:   Zhiqiang Liu <liuzhiqiang26@huawei.com>
Message-ID: <cd71d0fa-31d1-5cd8-74a1-8b124724b3b1@huawei.com>
Date:   Thu, 25 Mar 2021 09:21:50 +0800
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On 2021/3/22 22:22, Mike Snitzer wrote:
> On Mon, Mar 22 2021 at  4:11am -0400,
> Christoph Hellwig <hch@infradead.org> wrote:
> 
>> On Sat, Mar 20, 2021 at 03:19:23PM +0800, Zhiqiang Liu wrote:
>>> From: Zhiqiang Liu <liuzhiqiang26@huawei.com>
>>>
>>> When we make IO stress test on multipath device, there will
>>> be a metadata err because of wrong path. In the test, we
>>> concurrent execute 'iscsi device login|logout' and
>>> 'multipath -r' command with IO stress on multipath device.
>>> In some case, systemd-udevd may have not time to process
>>> uevents of iscsi device logout|login, and then 'multipath -r'
>>> command triggers multipathd daemon calls ioctl to load table
>>> with incorrect old device info from systemd-udevd.
>>> Then, one iscsi path may be incorrectly attached to another
>>> multipath which has different uuid. Finally, the metadata err
>>> occurs when umounting filesystem to down write metadata on
>>> the iscsi device which is actually not owned by the multipath
>>> device.
>>>
>>> So we need to check whether all pgpaths of one multipath have
>>> the same uuid, if not, we should throw a error.
>>>
>>> Signed-off-by: Zhiqiang Liu <liuzhiqiang26@huawei.com>
>>> Signed-off-by: lixiaokeng <lixiaokeng@huawei.com>
>>> Signed-off-by: linfeilong <linfeilong@huawei.com>
>>> Signed-off-by: Wubo <wubo40@huawei.com>
>>> ---
>>>  drivers/md/dm-mpath.c   | 52 +++++++++++++++++++++++++++++++++++++++++
>>>  drivers/scsi/scsi_lib.c |  1 +
>>>  2 files changed, 53 insertions(+)
>>>
>>> diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
>>> index bced42f082b0..f0b995784b53 100644
>>> --- a/drivers/md/dm-mpath.c
>>> +++ b/drivers/md/dm-mpath.c
>>> @@ -24,6 +24,7 @@
>>>  #include <linux/workqueue.h>
>>>  #include <linux/delay.h>
>>>  #include <scsi/scsi_dh.h>
>>> +#include <linux/dm-ioctl.h>
>>>  #include <linux/atomic.h>
>>>  #include <linux/blk-mq.h>
>>>
>>> @@ -1169,6 +1170,45 @@ static int parse_features(struct dm_arg_set *as, struct multipath *m)
>>>  	return r;
>>>  }
>>>
>>> +#define SCSI_VPD_LUN_ID_PREFIX_LEN 4
>>> +#define MPATH_UUID_PREFIX_LEN 7
>>> +static int check_pg_uuid(struct priority_group *pg, char *md_uuid)
>>> +{
>>> +	char pgpath_uuid[DM_UUID_LEN] = {0};
>>> +	struct request_queue *q;
>>> +	struct pgpath *pgpath;
>>> +	struct scsi_device *sdev;
>>> +	ssize_t count;
>>> +	int r = 0;
>>> +
>>> +	list_for_each_entry(pgpath, &pg->pgpaths, list) {
>>> +		q = bdev_get_queue(pgpath->path.dev->bdev);
>>> +		sdev = scsi_device_from_queue(q);
>>
>> Common dm-multipath code should never poke into scsi internals.  This
>> is something for the device handler to check.  It probably also won't
>> work for all older devices.
> 
> Definitely.
> 
> But that aside, userspace (multipathd) _should_ be able to do extra
> validation, _before_ pushing down a new table to the kernel, rather than
> forcing the kernel to do it.

As your said, it is better to do extra validation in userspace (multipathd).
However, in some cases, the userspace cannot see the real-time present devices
info as Martin (committer of multipath-tools) said.
In addition, the kernel can see right device info in the table at any time,
so the uuid check in kernel can ensure one multipath is composed with paths mapped to
the same device.

Considering the severity of the wrong path in multipath, I think it worths more
checking.

Regards
Zhiqiang Liu.


> 
> .
>