linux-kernel - Re: [PATCH v3 1/7] seqnum_ops: Introduce Sequence Number Ops

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Message-ID: <YB0WzBnLd+OcpxEE@kroah.com>
Date:   Fri, 5 Feb 2021 10:58:36 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Shuah Khan <skhan@...uxfoundation.org>
Cc:     corbet@....net, peterz@...radead.org, keescook@...omium.org,
        rafael@...nel.org, lenb@...nel.org, james.morse@....com,
        tony.luck@...el.com, bp@...en8.de, devel@...verdev.osuosl.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-acpi@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v3 1/7] seqnum_ops: Introduce Sequence Number Ops

On Wed, Feb 03, 2021 at 11:11:57AM -0700, Shuah Khan wrote:
> +static inline u32 seqnum32_inc(struct seqnum32 *seq)
> +{
> +	atomic_t val = ATOMIC_INIT(seq->seqnum);
> +
> +	seq->seqnum = (u32) atomic_inc_return(&val);
> +	if (seq->seqnum >= UINT_MAX)
> +		pr_info("Sequence Number overflow %u detected\n",
> +			seq->seqnum);
> +	return seq->seqnum;

As Peter points out, this is doing doing what you think it is doing :(

Why do you not just have seq->seqnum be a real atomic variable?  Trying
to switch to/from one like this does not work as there is no
"atomic-ness" happening here at all.

Oh, and checkpatch should have complained about the extra ' ' in your
cast :)

thanks,

greg k-h