The patch titled
Subject: squashfs: fix cache race with migration
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
squashfs-fix-cache-race-with-migration.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/squashfs-fix-cache-race-with-migration.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Vincent Whitchurch <vincent.whitchurch@xxxxxxxx>
Subject: squashfs: fix cache race with migration
Date: Thu, 29 Jun 2023 16:17:57 +0200
Migration replaces the page in the mapping before copying the contents and
the flags over from the old page, so check that the page in the page cache
is really up to date before using it. Without this, stressing squashfs
reads with parallel compaction sometimes results in squashfs reporting
data corruption.
Link: https://lkml.kernel.org/r/20230629-squashfs-cache-migration-v1-1-d50ebe55099d@xxxxxxxx
Fixes: e994f5b677ee ("squashfs: cache partial compressed blocks")
Signed-off-by: Vincent Whitchurch <vincent.whitchurch@xxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Phillip Lougher <phillip@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/squashfs/block.c | 27 +++++++++++++++++++++++----
1 file changed, 23 insertions(+), 4 deletions(-)
--- a/fs/squashfs/block.c~squashfs-fix-cache-race-with-migration
+++ a/fs/squashfs/block.c
@@ -166,6 +166,26 @@ static int squashfs_bio_read_cached(stru
return 0;
}
+static struct page *squashfs_get_cache_page(struct address_space *mapping,
+ pgoff_t index)
+{
+ struct page *page;
+
+ if (!mapping)
+ return NULL;
+
+ page = find_get_page(mapping, index);
+ if (!page)
+ return NULL;
+
+ if (!PageUptodate(page)) {
+ put_page(page);
+ return NULL;
+ }
+
+ return page;
+}
+
static int squashfs_bio_read(struct super_block *sb, u64 index, int length,
struct bio **biop, int *block_offset)
{
@@ -190,11 +210,10 @@ static int squashfs_bio_read(struct supe
for (i = 0; i < page_count; ++i) {
unsigned int len =
min_t(unsigned int, PAGE_SIZE - offset, total_len);
- struct page *page = NULL;
+ pgoff_t index = (read_start >> PAGE_SHIFT) + i;
+ struct page *page;
- if (cache_mapping)
- page = find_get_page(cache_mapping,
- (read_start >> PAGE_SHIFT) + i);
+ page = squashfs_get_cache_page(cache_mapping, index);
if (!page)
page = alloc_page(GFP_NOIO);
_
Patches currently in -mm which might be from vincent.whitchurch@xxxxxxxx are
squashfs-fix-cache-race-with-migration.patch
