From: Eryu Guan Date: Wed, 24 May 2017 22:02:20 +0000 (-0400) Subject: ext4: fix off-by-one on max nr_pages in ext4_find_unwritten_pgoff() X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=624327f8794704c5066b11a52f9da6a09dce7f9a;p=GitHub%2Fmoto-9609%2Fandroid_kernel_motorola_exynos9610.git ext4: fix off-by-one on max nr_pages in ext4_find_unwritten_pgoff() ext4_find_unwritten_pgoff() is used to search for offset of hole or data in page range [index, end] (both inclusive), and the max number of pages to search should be at least one, if end == index. Otherwise the only page is missed and no hole or data is found, which is not correct. When block size is smaller than page size, this can be demonstrated by preallocating a file with size smaller than page size and writing data to the last block. E.g. run this xfs_io command on a 1k block size ext4 on x86_64 host. # xfs_io -fc "falloc 0 3k" -c "pwrite 2k 1k" \ -c "seek -d 0" /mnt/ext4/testfile wrote 1024/1024 bytes at offset 2048 1 KiB, 1 ops; 0.0000 sec (42.459 MiB/sec and 43478.2609 ops/sec) Whence Result DATA EOF Data at offset 2k was missed, and lseek(2) returned ENXIO. This is unconvered by generic/285 subtest 07 and 08 on ppc64 host, where pagesize is 64k. Because a recent change to generic/285 reduced the preallocated file size to smaller than 64k. Signed-off-by: Eryu Guan Signed-off-by: Theodore Ts'o Reviewed-by: Jan Kara --- diff --git a/fs/ext4/file.c b/fs/ext4/file.c index 2b00bf84c05b..02ce7e7bbdf5 100644 --- a/fs/ext4/file.c +++ b/fs/ext4/file.c @@ -481,7 +481,7 @@ static int ext4_find_unwritten_pgoff(struct inode *inode, int i, num; unsigned long nr_pages; - num = min_t(pgoff_t, end - index, PAGEVEC_SIZE); + num = min_t(pgoff_t, end - index, PAGEVEC_SIZE - 1) + 1; nr_pages = pagevec_lookup(&pvec, inode->i_mapping, index, (pgoff_t)num); if (nr_pages == 0)