From: Andrew Morton <akpm@linux-foundation.org>
To: Larry Chen <lchen@suse.com>
Cc: mfasheh@versity.com, jlbec@evilplan.org,
linux-kernel@vger.kernel.org, ocfs2-devel@oss.oracle.com
Subject: Re: [PATCH] ocfs2: ocfs2_inode_lock_tracker does not distinguish lock level
Date: Thu, 10 May 2018 14:49:44 -0700 [thread overview]
Message-ID: <20180510144944.d0842b82b99a471dbbc745ad@linux-foundation.org> (raw)
In-Reply-To: <20180510053230.17217-1-lchen@suse.com>
On Thu, 10 May 2018 13:32:30 +0800 Larry Chen <lchen@suse.com> wrote:
> ocfs2_inode_lock_tracker as a variant of ocfs2_inode_lock,
> is used to prevent deadlock due to recursive lock acquisition.
>
> But this function does not distinguish
> whether the requested level is EX or PR.
>
> If a RP lock has been attained, this function
> will immediately return success afterwards even
> an EX lock is requested.
>
> But actually the return value does not mean that
> the process got a EX lock, because ocfs2_inode_lock
> has not been called.
>
> When taking lock levels into account, we face some different situations.
> 1. no lock is held
> In this case, just lock the inode and return 0
>
> 2. We are holding a lock
> For this situation, things diverges into several cases
>
> wanted holding what to do
> ex ex see 2.1 below
> ex pr see 2.2 below
> pr ex see 2.1 below
> pr pr see 2.1 below
>
> 2.1 lock level that is been held is compatible
> with the wanted level, so no lock action will be tacken.
>
> 2.2 Otherwise, an upgrade is needed, but it is forbidden.
>
> Reason why upgrade within a process is forbidden is that
> lock upgrade may cause dead lock. The following illustrate
> how it happens.
>
> process 1 process 2
> ocfs2_inode_lock_tracker(ex=0)
> <====== ocfs2_inode_lock_tracker(ex=1)
>
> ocfs2_inode_lock_tracker(ex=1)
>
Nice changelog, but it gives no information about the severity of the
bug: how often does it hit and what is the end-user impact.
This info is needed so that I and others can decide which kernel
version(s) need the patch, so please always include it when fixing a
bug, thanks.
next prev parent reply other threads:[~2018-05-10 21:49 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-05-10 5:32 [PATCH] ocfs2: ocfs2_inode_lock_tracker does not distinguish lock level Larry Chen
2018-05-10 7:49 ` [Ocfs2-devel] " Gang He
2018-05-10 21:49 ` Andrew Morton [this message]
2018-05-11 4:16 ` Larry Chen
2018-05-11 21:22 ` Andrew Morton
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