linux-kernel - Re: [PATCH 4/4] dm: convert table_device.count from atomic_t to refcount

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Message-ID: <20171124140413.GG5952@agk-dp.fab.redhat.com>
Date:   Fri, 24 Nov 2017 14:04:13 +0000
From:   Alasdair G Kergon <agk@...hat.com>
To:     "Reshetova, Elena" <elena.reshetova@...el.com>
Cc:     Zdenek Kabelac <zkabelac@...hat.com>,
        "dm-devel@...hat.com" <dm-devel@...hat.com>,
        "linux-bcache@...r.kernel.org" <linux-bcache@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-raid@...r.kernel.org" <linux-raid@...r.kernel.org>,
        "kent.overstreet@...il.com" <kent.overstreet@...il.com>,
        "koverstreet@...gle.com" <koverstreet@...gle.com>,
        "ejt@...hat.com" <ejt@...hat.com>,
        "snitzer@...hat.com" <snitzer@...hat.com>,
        "shli@...nel.org" <shli@...nel.org>,
        "agk@...hat.com" <agk@...hat.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "keescook@...omium.org" <keescook@...omium.org>
Subject: Re: [PATCH 4/4] dm: convert table_device.count from atomic_t to
        refcount_t

On Fri, Nov 24, 2017 at 08:29:42AM +0000, Reshetova, Elena wrote:
> By looking at the code, I don't see where the change in the reference counting
> could have caused this. 
 
The cause was the bug I identified in patch 3, not this patch.

The regression is easily hit - tables that reference the same underlying device
more than once are very common.

Alasdair