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Date:   Wed, 15 Apr 2020 13:25:03 +0000
From:   Luis Chamberlain <mcgrof@kernel.org>
To:     Christoph Hellwig <hch@infradead.org>
Cc:     axboe@kernel.dk, viro@zeniv.linux.org.uk, bvanassche@acm.org,
        gregkh@linuxfoundation.org, rostedt@goodmis.org, mingo@redhat.com,
        jack@suse.cz, ming.lei@redhat.com, nstange@suse.de,
        akpm@linux-foundation.org, mhocko@suse.com, yukuai3@huawei.com,
        linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Omar Sandoval <osandov@fb.com>,
        Hannes Reinecke <hare@suse.com>,
        Michal Hocko <mhocko@kernel.org>
Subject: Re: [PATCH 3/5] blktrace: refcount the request_queue during ioctl
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On Wed, Apr 15, 2020 at 05:39:25AM -0700, Christoph Hellwig wrote:
> On Wed, Apr 15, 2020 at 12:34:34PM +0000, Luis Chamberlain wrote:
> > I'll pile up a fix. I've also considered doing a full review of callers
> > outside of the core block layer using it, and maybe just unexporting
> > this. It was originally exported due to commit d86e0e83b ("block: export
> > blk_{get,put}_queue()") to fix a scsi bug, but I can't find such
> > respective fix. I suspec that using bdgrab()/bdput() seems more likely
> > what drivers should be using. That would allow us to keep this
> > functionality internal.
> > 
> > Think that's worthy review?
> 
> Probably.  I did in fact very quickly look into that but then gave
> up due to the fair amount of modular users.

Alright, then might as well then verify if the existing practice of
bdgrab()/bdput() is indeed valid logic, as otherwise we'd be puting
the atomic context / sleep concern to bdput(). As noted earlier I
am able to confirm easily that bdgrab() can be called in atomic contex,
however I cannot easily yet vet for *why* this was a safe assumption for
bdput().

  Luis