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Date:   Tue, 18 Aug 2020 03:22:49 +0100
From:   Al Viro <>
To:     "Eric W. Biederman" <>
        Linus Torvalds <>,
        Christian Brauner <>,
        Oleg Nesterov <>,
        Cyrill Gorcunov <>,
        Jann Horn <>, Kees Cook <>,
        Daniel P. Berrangé <>,
        Jeff Layton <>,
        Miklos Szeredi <>,
        Matthew Wilcox <>,
        "J. Bruce Fields" <>,
        Matthew Wilcox <>,
        Trond Myklebust <>,
        Chris Wright <>,
        Alexei Starovoitov <>,
        Daniel Borkmann <>,
        Martin KaFai Lau <>,
        Song Liu <>, Yonghong Song <>,
        Andrii Nakryiko <>,
        John Fastabend <>,
        KP Singh <>
Subject: Re: [PATCH 10/17] proc/fd: In proc_readfd_common use fnext_task

On Mon, Aug 17, 2020 at 05:04:18PM -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.
> Using fnext_task simplifies proc_readfd_common, by moving the checking
> for the maximum file descritor into the generic code, and by
> remvoing the need for capturing and releasing a reference on
> files_struct.

Yecchhh...  So you keep locking/unlocking the damn thing for each

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