Date: Wed, 12 Oct 2016 14:41:12 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: zijun_hu <zijun_hu@zoho.com>
Cc: tj@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        zijun_hu@htc.com, cl@linux.com
Subject: Re: [RFC v2 PATCH] mm/percpu.c: fix panic triggered by BUG_ON()
 falsely
Message-Id: <20161012144112.0494082cf4cbd07609d2405d@linux-foundation.org>
In-Reply-To: <57FCF07C.2020103@zoho.com>
References: <57FCF07C.2020103@zoho.com>
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On Tue, 11 Oct 2016 22:00:28 +0800 zijun_hu <zijun_hu@zoho.com> wrote:

> as shown by pcpu_build_alloc_info(), the number of units within a percpu
> group is educed by rounding up the number of CPUs within the group to
> @upa boundary, therefore, the number of CPUs isn't equal to the units's
> if it isn't aligned to @upa normally. however, pcpu_page_first_chunk()
> uses BUG_ON() to assert one number is equal the other roughly, so a panic
> is maybe triggered by the BUG_ON() falsely.
> 
> in order to fix this issue, the number of CPUs is rounded up then compared
> with units's, the BUG_ON() is replaced by warning and returning error code
> as well to keep system alive as much as possible.

Under what circumstances is the triggered?  In other words, what are
the end-user visible effects of the fix?

I mean, this is pretty old code (isn't it?) so what are you doing that
triggers this?