Date:   Thu, 25 Nov 2021 03:32:31 +0000
From:   Matthew Wilcox <willy@infradead.org>
To:     John Hubbard <jhubbard@nvidia.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>, cgel.zte@gmail.com,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        chiminghao <chi.minghao@zte.com.cn>,
        Zeal Robot <zealci@zte.com.cn>
Subject: Re: [PATCH] mm: Use BUG_ON instead of if condition followed by BUG
Message-ID: <YZ8Dz/85n1Dogy87@casper.infradead.org>
References: <20211124030849.34998-1-chi.minghao@zte.com.cn>
 <YZ483gwnwTysPt0G@casper.infradead.org>
 <20211124142751.e48cdcc3aea9e0ef899f4347@linux-foundation.org>
 <348f3a1f-c7d3-c21f-419d-7acd2e5290b6@nvidia.com>
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On Wed, Nov 24, 2021 at 02:45:59PM -0800, John Hubbard wrote:
> @@ -2201,13 +2201,12 @@ static int __ref try_remove_memory(u64 start, u64 size)
> */
> void __remove_memory(u64 start, u64 size)
> {
> -
> +       int ret = try_remove_memory(start, size);
> /*
> * trigger BUG() if some memory is not offlined prior to calling this
> * function
> */
> -       if (try_remove_memory(start, size))
> -               BUG();
> +       BUG_ON(ret);
> }

I'd rather leave it the way it is.  I don't see why the version you
propose is better.

> ...and by the way, while going to type that, I immediately stumbled upon
> another pre-existing case of this sort of thing, in try_remove_memory(),
> which does this:
> 
> static int __ref try_remove_memory(u64 start, u64 size)
> {
> 	struct vmem_altmap mhp_altmap = {};
> 	struct vmem_altmap *altmap = NULL;
> 	unsigned long nr_vmemmap_pages;
> 	int rc = 0, nid = NUMA_NO_NODE;
> 
> 	BUG_ON(check_hotplug_memory_range(start, size));

That needs to be fixed.