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Subject: Re: [PATCH 4.19 082/131] nvme: fix possible deadlock when I/O is
 blocked
To:     Pavel Machek <pavel@ucw.cz>, Sasha Levin <sashal@kernel.org>
Cc:     linux-kernel@vger.kernel.org, stable@vger.kernel.org,
        Anton Eidelman <anton@lightbitslabs.com>,
        Christoph Hellwig <hch@lst.de>
References: <20200629153502.2494656-1-sashal@kernel.org>
 <20200629153502.2494656-83-sashal@kernel.org> <20200702211743.GE5787@amd>
From:   Sagi Grimberg <sagi@grimberg.me>
Message-ID: <e05ddf9e-1804-d297-47f4-c422d4f98cfb@grimberg.me>
Date:   Thu, 2 Jul 2020 15:15:48 -0700
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> Hi!
> 
>> From: Sagi Grimberg <sagi@grimberg.me>
>>
>> [ Upstream commit 3b4b19721ec652ad2c4fe51dfbe5124212b5f581 ]
>>
>> Revert fab7772bfbcf ("nvme-multipath: revalidate nvme_ns_head gendisk
>> in nvme_validate_ns")
>>
>> When adding a new namespace to the head disk (via nvme_mpath_set_live)
>> we will see partition scan which triggers I/O on the mpath device node.
>> This process will usually be triggered from the scan_work which holds
>> the scan_lock. If I/O blocks (if we got ana change currently have only
>> available paths but none are accessible) this can deadlock on the head
>> disk bd_mutex as both partition scan I/O takes it, and head disk revalidation
>> takes it to check for resize (also triggered from scan_work on a different
>> path). See trace [1].
>>
>> The mpath disk revalidation was originally added to detect online disk
>> size change, but this is no longer needed since commit cb224c3af4df
>> ("nvme: Convert to use set_capacity_revalidate_and_notify") which already
>> updates resize info without unnecessarily revalidating the disk (the
> 
> Unfortunately, v4.19-stable does not contain cb224c3af4df. According
> to changelog, it seems it should be cherry-picked?

You are absolutely right,

The reference commit is a part of the series:
78317c5d58e6 ("scsi: Convert to use set_capacity_revalidate_and_notify")
cb224c3af4df ("nvme: Convert to use set_capacity_revalidate_and_notify")
3cbc28bb902b ("xen-blkfront.c: Convert to use 
set_capacity_revalidate_and_notify")
662155e2898d ("virtio_blk.c: Convert to use 
set_capacity_revalidate_and_notify")
e598a72faeb5 ("block/genhd: Notify udev about capacity change")

It would be cool if they are cherry picked, although they don't qualify
as stable patches per se...