linux-kernel - Re: [PATCH] fs: dcache: Avoid livelock between d_alloc_parallel and __d

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Message-ID: <20180213151608.GA17791@bombadil.infradead.org>
Date:   Tue, 13 Feb 2018 07:16:08 -0800
From:   Matthew Wilcox <willy@...radead.org>
To:     Will Deacon <will.deacon@....com>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH] fs: dcache: Avoid livelock between d_alloc_parallel and
 __d_add

On Tue, Feb 13, 2018 at 12:58:51PM +0000, Will Deacon wrote:
> This patch resolves the livelock by not taking hlist_bl_lock in
> d_alloc_parallel if the sequence counter is odd, since any subsequent
> masked comparison with i_dir_seq will fail anyway.
> 
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Al Viro <viro@...iv.linux.org.uk>
> Signed-off-by: Will Deacon <will.deacon@....com>

Reviewed-by: Matthew Wilcox <mawilcox@...rosoft.com>

I wonder whether it makes sense to turn i_dir_seq into a seqcount_t,
which would give us the lockdep checking as well.