linux-kernel - Re: [PATCH] files: Use rcu lock to get the file structures for better performance

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Date:   Thu, 21 May 2020 08:21:17 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Muchun Song <songmuchun@...edance.com>
Cc:     adobriyan@...il.com, ast@...nel.org, daniel@...earbox.net,
        kafai@...com, songliubraving@...com, yhs@...com, andriin@...com,
        john.fastabend@...il.com, kpsingh@...omium.org,
        ebiederm@...ssion.com, bernd.edlinger@...mail.de,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        netdev@...r.kernel.org, bpf@...r.kernel.org
Subject: Re: [PATCH] files: Use rcu lock to get the file structures for
 better performance

On Thu, May 21, 2020 at 08:38:35PM +0800, Muchun Song wrote:
> There is another safe way to get the file structure without
> holding the files->file_lock. That is rcu lock, and this way
> has better performance. So use the rcu lock instead of the
> files->file_lock.

What makes you think this is safe?  Are you actually seeing contention
on this spinlock?