linux-kernel - Re: [PATCH] mm: page_alloc: check the order of compound page event when the order is 0

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Message-ID: <ZSmucNWBMj/mNVeE@dhcp-10-159-238-251.vpn.oracle.com>
Date:   Fri, 13 Oct 2023 13:54:08 -0700
From:   Vishal Moola <vishal.moola@...il.com>
To:     Hyesoo Yu <hyesoo.yu@...sung.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: page_alloc: check the order of compound page event
 when the order is 0

On Thu, Oct 12, 2023 at 10:11:06AM +0900, Hyesoo Yu wrote:
> For compound pages, the head sets the PG_head flag and
> the tail sets the compound_head to indicate the head page.
> If a user allocates a compound page and frees it with a different
> order, the compound page information will not be properly
> initialized. To detect this problem, compound_page(page) and
> the order are compared, but it is not checked when the order is 0.
> That error should be checked regardless of the order.

I believe all compound pages are order >= 1, so this error can't occur
when the order is 0.