linux-kernel - Re: [PATCH] sysfs: Replace %p with %pK in the warning of sysfs

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Date:   Fri, 23 Jun 2023 16:30:21 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Kyle Tso <kyletso@...gle.com>
Cc:     rafael@...nel.org, badhri@...gle.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sysfs: Replace %p with %pK in the warning of sysfs_emit*

On Fri, Jun 23, 2023 at 10:20:54PM +0800, Kyle Tso wrote:
> According to Documentation/core-api/printk-formats.rst, kernel pointers
> need to be printed with %pK format specifier to respect kptr_restrict in
> sysctl.
> 
> Also replace the function names in the strings with %s and __func__ as
> checkpatch.pl suggested.
> 
> Signed-off-by: Kyle Tso <kyletso@...gle.com>
> ---
>  fs/sysfs/file.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
> index a12ac0356c69..56712f0886ef 100644
> --- a/fs/sysfs/file.c
> +++ b/fs/sysfs/file.c
> @@ -732,7 +732,7 @@ int sysfs_emit(char *buf, const char *fmt, ...)
>  	int len;
>  
>  	if (WARN(!buf || offset_in_page(buf),
> -		 "invalid sysfs_emit: buf:%p\n", buf))
> +		 "invalid %s: buf:%pK\n", __func__, buf))

Wait, no, these are not going out in sysfs files, as they are still
going to dmesg, right?

So I think this line in the documentation matters:
	This modifier is *only* intended when producing content of a file read by
	userspace from e.g. procfs or sysfs, not for dmesg. Please refer to the
	section about %p above for discussion about how to manage hashing pointers
	in printk().

so %p should still be ok here, the hashed value will end up in the
kernerl log, which is what we want, and the WARN() traceback will show
the problem properly, right?

>  		return 0;
>  
>  	va_start(args, fmt);
> @@ -760,7 +760,7 @@ int sysfs_emit_at(char *buf, int at, const char *fmt, ...)
>  	int len;
>  
>  	if (WARN(!buf || offset_in_page(buf) || at < 0 || at >= PAGE_SIZE,
> -		 "invalid sysfs_emit_at: buf:%p at:%d\n", buf, at))
> +		 "invalid %s: buf:%pK at:%d\n", __func__, buf, at))


Same here, %p should be correct.

Sorry for missing this before.

greg k-h