linux-kernel - [PATCH] mm: cleancache: fix corruption on missed inode invalidation

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Message-Id: <20181112095734.17979-1-ptikhomirov@virtuozzo.com>
Date:   Mon, 12 Nov 2018 12:57:34 +0300
From:   Pavel Tikhomirov <ptikhomirov@...tuozzo.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Vasily Averin <vvs@...tuozzo.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Konstantin Khorenko <khorenko@...tuozzo.com>,
        Pavel Tikhomirov <ptikhomirov@...tuozzo.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Jan Kara <jack@...e.cz>, Matthew Wilcox <willy@...radead.org>,
        Andi Kleen <ak@...ux.intel.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] mm: cleancache: fix corruption on missed inode invalidation

If all pages are deleted from the mapping by memory reclaim and also
moved to the cleancache:

__delete_from_page_cache
  (no shadow case)
  unaccount_page_cache_page
    cleancache_put_page
  page_cache_delete
    mapping->nrpages -= nr
    (nrpages becomes 0)

We don't clean the cleancache for an inode after final file truncation
(removal).

truncate_inode_pages_final
  check (nrpages || nrexceptional) is false
    no truncate_inode_pages
      no cleancache_invalidate_inode(mapping)

These way when reading the new file created with same inode we may get
these trash leftover pages from cleancache and see wrong data instead of
the contents of the new file.

Fix it by always doing truncate_inode_pages which is already ready for
nrpages == 0 && nrexceptional == 0 case and just invalidates inode.

Fixes: commit 91b0abe36a7b ("mm + fs: store shadow entries in page cache")
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Johannes Weiner <hannes@...xchg.org>
Cc: Mel Gorman <mgorman@...hsingularity.net>
Cc: Jan Kara <jack@...e.cz>
Cc: Matthew Wilcox <willy@...radead.org>
Cc: Andi Kleen <ak@...ux.intel.com>
Cc: linux-mm@...ck.org
Cc: linux-kernel@...r.kernel.org
Reviewed-by: Vasily Averin <vvs@...tuozzo.com>
Reviewed-by: Andrey Ryabinin <aryabinin@...tuozzo.com>
Signed-off-by: Pavel Tikhomirov <ptikhomirov@...tuozzo.com>
---
 mm/truncate.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/truncate.c b/mm/truncate.c
index 45d68e90b703..4c56c19e76eb 100644
--- a/mm/truncate.c
+++ b/mm/truncate.c
@@ -517,9 +517,9 @@ void truncate_inode_pages_final(struct address_space *mapping)
 		 */
 		xa_lock_irq(&mapping->i_pages);
 		xa_unlock_irq(&mapping->i_pages);
-
-		truncate_inode_pages(mapping, 0);
 	}
+
+	truncate_inode_pages(mapping, 0);
 }
 EXPORT_SYMBOL(truncate_inode_pages_final);
 
-- 
2.17.1