mirror of
https://github.com/hardkernel/linux.git
synced 2026-06-06 10:58:48 +09:00
cb52ee334a
Directory block readahead uses a complex iteration mechanism to map between high-level directory blocks and underlying physical extents. This mechanism attempts to traverse the higher-level dir blocks in a manner that handles multi-fsb directory blocks and simultaneously maintains a reference to the corresponding physical blocks. This logic doesn't handle certain (discontiguous) physical extent layouts correctly with multi-fsb directory blocks. For example, consider the case of a 4k FSB filesystem with a 2 FSB (8k) directory block size and a directory with the following extent layout: EXT: FILE-OFFSET BLOCK-RANGE AG AG-OFFSET TOTAL 0: [0..7]: 88..95 0 (88..95) 8 1: [8..15]: 80..87 0 (80..87) 8 2: [16..39]: 168..191 0 (168..191) 24 3: [40..63]: 5242952..5242975 1 (72..95) 24 Directory block 0 spans physical extents 0 and 1, dirblk 1 lies entirely within extent 2 and dirblk 2 spans extents 2 and 3. Because extent 2 is larger than the directory block size, the readahead code erroneously assumes the block is contiguous and issues a readahead based on the physical mapping of the first fsb of the dirblk. This results in read verifier failure and a spurious corruption or crc failure, depending on the filesystem format. Further, the subsequent readahead code responsible for walking through the physical table doesn't correctly advance the physical block reference for dirblk 2. Instead of advancing two physical filesystem blocks, the first iteration of the loop advances 1 block (correctly), but the subsequent iteration advances 2 more physical blocks because the next physical extent (extent 3, above) happens to cover more than dirblk 2. At this point, the higher-level directory block walking is completely off the rails of the actual physical layout of the directory for the respective mapping table. Update the contiguous dirblock logic to consider the current offset in the physical extent to avoid issuing directory readahead to unrelated blocks. Also, update the mapping table advancing code to consider the current offset within the current dirblock to avoid advancing the mapping reference too far beyond the dirblock. Signed-off-by: Brian Foster <bfoster@redhat.com> Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.