From: Johannes Weiner <hannes@cmpxchg.org>
To: Song Liu <songliubraving@fb.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
open list <linux-kernel@vger.kernel.org>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
"matthew.wilcox@oracle.com" <matthew.wilcox@oracle.com>,
Kernel Team <Kernel-team@fb.com>,
"william.kucharski@oracle.com" <william.kucharski@oracle.com>,
"kirill.shutemov@linux.intel.com"
<kirill.shutemov@linux.intel.com>,
Hugh Dickins <hughd@google.com>
Subject: Re: [PATCH v3] mm,thp: recheck each page before collapsing file THP
Date: Mon, 21 Oct 2019 14:03:14 -0400 [thread overview]
Message-ID: <20191021180314.GA185593@cmpxchg.org> (raw)
In-Reply-To: <9DC29F5B-1DF5-408F-BEDF-FD1FBAAB1361@fb.com>
On Sat, Oct 19, 2019 at 05:24:00AM +0000, Song Liu wrote:
> In collapse_file(), for !is_shmem case, current check cannot guarantee
> the locked page is up-to-date. Specifically, xas_unlock_irq() should not
> be called before lock_page() and get_page(); and it is necessary to
> recheck PageUptodate() after locking the page.
>
> With this bug and CONFIG_READ_ONLY_THP_FOR_FS=y, madvise(HUGE)'ed .text
> may contain corrupted data. This is because khugepaged mistakenly
> collapses some not up-to-date sub pages into a huge page, and assumes the
> huge page is up-to-date. This will NOT corrupt data in the disk, because
> the page is read-only and never written back. Fix this by properly
> checking PageUptodate() after locking the page. This check replaces
> "VM_BUG_ON_PAGE(!PageUptodate(page), page);".
>
> Also, move PageDirty() check after locking the page. Current khugepaged
> should not try to collapse dirty file THP, because it is limited to
> read-only .text. Add a warning with the PageDirty() check as it should
> not happen. This warning is added after page_mapping() check, because
> if the page is truncated, it might be dirty.
>
> Fixes: 99cb0dbd47a1 ("mm,thp: add read-only THP support for (non-shmem) FS")
> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: Hugh Dickins <hughd@google.com>
> Cc: William Kucharski <william.kucharski@oracle.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Signed-off-by: Song Liu <songliubraving@fb.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
next prev parent reply other threads:[~2019-10-21 18:03 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-18 18:03 [PATCH v3] mm,thp: recheck each page before collapsing file THP Song Liu
2019-10-19 1:17 ` Andrew Morton
2019-10-19 5:24 ` Song Liu
2019-10-21 18:03 ` Johannes Weiner [this message]
2019-11-06 4:58 ` Andrew Morton
2019-11-06 5:45 ` Song Liu
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