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Subject: Re: filesystem corruption with "scsi: core: Reallocate device's
 budget map on queue depth change"
From:   James Bottomley <jejb@linux.ibm.com>
Reply-To: jejb@linux.ibm.com
To:     John Garry <john.garry@huawei.com>,
        Andrea Righi <andrea.righi@canonical.com>,
        Ming Lei <ming.lei@redhat.com>
Cc:     Martin Wilck <martin.wilck@suse.com>,
        Bart Van Assche <bvanassche@acm.org>,
        "Martin K. Petersen" <martin.petersen@oracle.com>,
        linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org
Date:   Wed, 30 Mar 2022 09:31:35 -0400
In-Reply-To: <08717833-19bb-8aaa-4f24-2989a9f56cd3@huawei.com>
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         <f7bacce8-b5e5-3ef1-e116-584c01533f69@huawei.com>
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         <08717833-19bb-8aaa-4f24-2989a9f56cd3@huawei.com>
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On Wed, 2022-03-30 at 13:59 +0100, John Garry wrote:
> On 30/03/2022 12:21, Andrea Righi wrote:
> > On Wed, Mar 30, 2022 at 11:38:02AM +0100, John Garry wrote:
> > > On 30/03/2022 11:11, Andrea Righi wrote:
> > > > Hello,
> > > > 
> > > > after this commit I'm experiencing some filesystem corruptions
> > > > at boot on a power9 box with an aacraid controller.
> > > > 
> > > > At the moment I'm running a 5.15.30 kernel; when the filesystem
> > > > is mounted at boot I see the following errors in the console:
> 
> About "scsi: core: Reallocate device's budget map on queue depth
> change" being added to a stable kernel, I am not sure if this was
> really a fix  or just a memory optimisation.

I can see how it becomes the problem: it frees and allocates a new
bitmap across a queue freeze, but bits in the old one might still be in
use.  This isn't a problem except when they return and we now possibly
see a tag greater than we think we can allocate coming back. 
Presumably we don't check this and we end up doing a write to
unallocated memory.

I think if you want to reallocate on queue depth reduction, you might
have to drain the queue as well as freeze it.

James