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Date:   Tue, 18 Aug 2020 12:43:45 +0200
From:   Christian Brauner <christian.brauner@ubuntu.com>
To:     "Eric W. Biederman" <ebiederm@xmission.com>
Cc:     linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        criu@openvz.org, bpf@vger.kernel.org,
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Subject: Re: [PATCH 12/17] proc/fd: In fdinfo seq_show don't use
 get_files_struct
Message-ID: <20200818104345.n5ugxlzuv5iuggqs@wittgenstein>
References: <87ft8l6ic3.fsf@x220.int.ebiederm.org>
 <20200817220425.9389-12-ebiederm@xmission.com>
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On Mon, Aug 17, 2020 at 05:04:20PM -0500, Eric W. Biederman wrote:
> When discussing[1] exec and posix file locks it was realized that none
> of the callers of get_files_struct fundamentally needed to call
> get_files_struct, and that by switching them to helper functions
> instead it will both simplify their code and remove unnecessary
> increments of files_struct.count.  Those unnecessary increments can
> result in exec unnecessarily unsharing files_struct which breaking
> posix locks, and it can result in fget_light having to fallback to
> fget reducing system performance.
> 
> Instead hold task_lock for the duration that task->files needs to be
> stable in seq_show.  The task_lock was already taken in
> get_files_struct, and so skipping get_files_struct performs less work
> overall, and avoids the problems with the files_struct reference
> count.
> 
> [1] https://lkml.kernel.org/r/20180915160423.GA31461@redhat.com
> Suggested-by: Oleg Nesterov <oleg@redhat.com>
> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
> ---

Acked-by: Christian Brauner <christian.brauner@ubuntu.com>