linux-kernel - Re: [PATCH 15/23] seq_file: switch over direct seq_read method calls to seq_read

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Date:   Fri, 10 Jul 2020 14:58:13 +0200
From:   Christoph Hellwig <hch@....de>
To:     Jon Hunter <jonathanh@...dia.com>
Cc:     Christoph Hellwig <hch@....de>, Al Viro <viro@...iv.linux.org.uk>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Matthew Wilcox <willy@...radead.org>,
        Kees Cook <keescook@...omium.org>,
        Iurii Zaikin <yzaikin@...gle.com>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-tegra <linux-tegra@...r.kernel.org>
Subject: Re: [PATCH 15/23] seq_file: switch over direct seq_read method
 calls to seq_read_iter

On Fri, Jul 10, 2020 at 01:55:29PM +0100, Jon Hunter wrote:
> Following this change, I have noticed that several debugfs entries can
> no longer be read on some Tegra platforms. For example ...
> 
> $ sudo cat /sys/kernel/debug/usb/xhci/3530000.usb/event-ring/cycle
> cat: /sys/kernel/debug/usb/xhci/3530000.usb/event-ring/cycle: Invalid
> argument
> 
> $ sudo cat /sys/kernel/debug/emc/available_rates
> 
> 
> cat: /sys/kernel/debug/emc/available_rates: Invalid argument
> 
> $ sudo cat /sys/kernel/debug/bpmp/debug/proc/testint
> cat: /sys/kernel/debug/bpmp/debug/proc/testint: Invalid argument
> 
> $ sudo cat /sys/kernel/debug/pcie/ports
> 
> 
> cat: /sys/kernel/debug/pcie/ports: Invalid argument
> 
> I have reverted the above drivers to use seq_read() instead of
> seq_read_iter() and they work again. Have you seen any problems with this?

I haven't seen any of that.  But some of these files should also
exist on x86, so let me try to reproduce it.