linux-kernel - Re: [PATCH 3/5] blktrace: refcount the request

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Message-ID: <20200415132503.GX11244@42.do-not-panic.com>
Date:   Wed, 15 Apr 2020 13:25:03 +0000
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     axboe@...nel.dk, viro@...iv.linux.org.uk, bvanassche@....org,
        gregkh@...uxfoundation.org, rostedt@...dmis.org, mingo@...hat.com,
        jack@...e.cz, ming.lei@...hat.com, nstange@...e.de,
        akpm@...ux-foundation.org, mhocko@...e.com, yukuai3@...wei.com,
        linux-block@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Omar Sandoval <osandov@...com>,
        Hannes Reinecke <hare@...e.com>,
        Michal Hocko <mhocko@...nel.org>
Subject: Re: [PATCH 3/5] blktrace: refcount the request_queue during ioctl

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