linux-kernel - Re: [PATCH] sd: sd_open: prevent device removal during sd

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Date:   Fri, 3 Sep 2021 05:38:34 +0100
From:   Christoph Hellwig <hch@...radead.org>
To:     Christian L?hle <CLoehle@...erstone.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        "martin.petersen@...cle.com" <martin.petersen@...cle.com>,
        "jejb@...ux.ibm.com" <jejb@...ux.ibm.com>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH] sd: sd_open: prevent device removal during sd_open

On Thu, Sep 02, 2021 at 01:57:13PM +0000, Christian L?hle wrote:
> sd and parent devices must not be removed as sd_open checks for events
> 
> sd_need_revalidate and sd_revalidate_disk traverse the device path
> to check for event changes. If during this, e.g. the scsi host is being
> removed and its resources freed, this traversal crashes.
> Locking with scan_mutex for just a scsi disk open may seem blunt, but there
> does not seem to be a more granular option. Also opening /dev/sdX directly
> happens rarely enough that this shouldn't cause any issues.

Can you please root cause how the device could not be valid, as that
should not happen?

>
> The issue occurred on an older kernel with the following trace:
> stack segment: 0000 [#1] PREEMPT SMP PTI
> CPU: 1 PID: 121457 Comm: python3 Not tainted 4.14.238hyLinux #1

.. preferably with a current mainline kernel as things changed a lot
in this area.