linux-kernel - MREMAP_DONTUNMAP corrupts initial mapping

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Message-ID: <aee53ac3-6d25-5009-7416-3f7c5fe1f989@yandex.ru>
Date:   Thu, 30 Mar 2023 17:38:15 +0500
From:   stsp <stsp2@...dex.ru>
To:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Cc:     linux-mm@...ck.org
Subject: MREMAP_DONTUNMAP corrupts initial mapping

Hello.

Attached is a small test-case that
demonstrates the problem.
The problem happens if you change
some data in a file-backed private
mapping and then use mremap on
it with MREMAP_DONTUNMAP flag.
The result is:
- destination copy is valid
- source copy restored from the original file

So the 2 copies do not match.

View attachment "mretst.c" of type "text/x-csrc" (838 bytes)