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Date:   Wed, 3 Feb 2021 10:04:05 +0100
From:   Greg KH <gregkh@linuxfoundation.org>
To:     Nicolas Boichat <drinkcat@chromium.org>
Cc:     "Darrick J. Wong" <djwong@kernel.org>,
        linux-fsdevel@vger.kernel.org, lkml <linux-kernel@vger.kernel.org>,
        Amir Goldstein <amir73il@gmail.com>,
        Dave Chinner <dchinner@redhat.com>,
        Luis Lozano <llozano@chromium.org>, iant@google.com
Subject: Re: [BUG] copy_file_range with sysfs file as input
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References: <CANMq1KDZuxir2LM5jOTm0xx+BnvW=ZmpsG47CyHFJwnw7zSX6Q@mail.gmail.com>
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On Mon, Jan 25, 2021 at 03:54:31PM +0800, Nicolas Boichat wrote:
> Hi copy_file_range experts,
> 
> We hit this interesting issue when upgrading Go compiler from 1.13 to
> 1.15 [1]. Basically we use Go's `io.Copy` to copy the content of
> `/sys/kernel/debug/tracing/trace` to a temporary file.

Nit, the above file is NOT a sysfs file.  Odds are it is either a
debugfs, or a tracefs file, please check your mounts to determine which
it is, as that matters a lot on the kernel backend side for trying to
figure out what is going on here :)

thanks,

greg k-h