linux-kernel - [PATCH] squashfs: avoid bio_alloc() failure with 1Mbyte blocks

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Date:   Sat, 15 Aug 2020 04:56:37 +0100
From:   Phillip Lougher <phillip@...ashfs.org.uk>
To:     linux-kernel@...r.kernel.org
Cc:     akpm@...ux-foundation.org, pliard@...gle.com, hch@....de,
        adrien+dev@...ischi.me, groeck@...omium.org, drosen@...gle.com,
        Phillip Lougher <phillip@...ashfs.org.uk>,
        Nicolas Prochazka <nicolas.prochazka@...il.com>,
        Tomoatsu Shimada <shimada@...brix.com>
Subject: [PATCH] squashfs: avoid bio_alloc() failure with 1Mbyte blocks

This is a regression introduced by the "migrate from ll_rw_block usage
to BIO" patch.

Bio_alloc() is limited to 256 pages (1 Mbyte).   This can cause a
failure when reading 1 Mbyte block filesystems.  The problem is
a datablock can be fully (or almost uncompressed), requiring 256
pages, but, because blocks are not aligned to page boundaries, it
may require 257 pages to read.

Bio_kmalloc() can handle 1024 pages, and so use this for the
edge condition.

Reported-by: Nicolas Prochazka <nicolas.prochazka@...il.com>
Reported-by: Tomoatsu Shimada <shimada@...brix.com>
Signed-off-by: Phillip Lougher <phillip@...ashfs.org.uk>
---
 fs/squashfs/block.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/fs/squashfs/block.c b/fs/squashfs/block.c
index 76bb1c846845..8a19773b5a0b 100644
--- a/fs/squashfs/block.c
+++ b/fs/squashfs/block.c
@@ -87,7 +87,11 @@ static int squashfs_bio_read(struct super_block *sb, u64 index, int length,
 	int error, i;
 	struct bio *bio;
 
-	bio = bio_alloc(GFP_NOIO, page_count);
+	if (page_count <= BIO_MAX_PAGES)
+		bio = bio_alloc(GFP_NOIO, page_count);
+	else
+		bio = bio_kmalloc(GFP_NOIO, page_count);
+
 	if (!bio)
 		return -ENOMEM;
 
-- 
2.20.1