linux-toradex.git/fs/xfs/xfs_dir2_readdir.c, branch v4.4.95

xfs: prevent multi-fsb dir readahead from reading random blocks

2017-06-07T10:06:02+00:00

commit cb52ee334a45ae6c78a3999e4b473c43ddc528f4 upstream.

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 
Reviewed-by: Darrick J. Wong 
Signed-off-by: Darrick J. Wong 
Signed-off-by: Greg Kroah-Hartman

xfs: handle array index overrun in xfs_dir2_leaf_readbuf()

2017-06-07T10:06:02+00:00

commit 023cc840b40fad95c6fe26fff1d380a8c9d45939 upstream.

Carlos had a case where "find" seemed to start spinning
forever and never return.

This was on a filesystem with non-default multi-fsb (8k)
directory blocks, and a fragmented directory with extents
like this:

0:[0,133646,2,0]
1:[2,195888,1,0]
2:[3,195890,1,0]
3:[4,195892,1,0]
4:[5,195894,1,0]
5:[6,195896,1,0]
6:[7,195898,1,0]
7:[8,195900,1,0]
8:[9,195902,1,0]
9:[10,195908,1,0]
10:[11,195910,1,0]
11:[12,195912,1,0]
12:[13,195914,1,0]
...

i.e. the first extent is a contiguous 2-fsb dir block, but
after that it is fragmented into 1 block extents.

At the top of the readdir path, we allocate a mapping array
which (for this filesystem geometry) can hold 10 extents; see
the assignment to map_info->map_size.  During readdir, we are
therefore able to map extents 0 through 9 above into the array
for readahead purposes.  If we count by 2, we see that the last
mapped index (9) is the first block of a 2-fsb directory block.

At the end of xfs_dir2_leaf_readbuf() we have 2 loops to fill
more readahead; the outer loop assumes one full dir block is
processed each loop iteration, and an inner loop that ensures
that this is so by advancing to the next extent until a full
directory block is mapped.

The problem is that this inner loop may step past the last
extent in the mapping array as it tries to reach the end of
the directory block.  This will read garbage for the extent
length, and as a result the loop control variable 'j' may
become corrupted and never fail the loop conditional.

The number of valid mappings we have in our array is stored
in map->map_valid, so stop this inner loop based on that limit.

There is an ASSERT at the top of the outer loop for this
same condition, but we never made it out of the inner loop,
so the ASSERT never fired.

Huge appreciation for Carlos for debugging and isolating
the problem.

Debugged-and-analyzed-by: Carlos Maiolino 
Signed-off-by: Eric Sandeen 
Tested-by: Carlos Maiolino 
Reviewed-by: Carlos Maiolino 
Reviewed-by: Bill O'Donnell 
Reviewed-by: Darrick J. Wong 
Signed-off-by: Darrick J. Wong 
Signed-off-by: Greg Kroah-Hartman

xfs: per-filesystem stats counter implementation

2015-10-12T07:21:22+00:00

This patch modifies the stats counting macros and the callers
to those macros to properly increment, decrement, and add-to
the xfs stats counts. The counts for global and per-fs stats
are correctly advanced, and cleared by writing a "1" to the
corresponding clear file.

global counts: /sys/fs/xfs/stats/stats
per-fs counts: /sys/fs/xfs/sda*/stats/stats

global clear:  /sys/fs/xfs/stats/stats_clear
per-fs clear:  /sys/fs/xfs/sda*/stats/stats_clear

[dchinner: cleaned up macro variables, removed CONFIG_FS_PROC around
 stats structures and macros. ]

Signed-off-by: Bill O'Donnell 
Reviewed-by: Eric Sandeen 
Signed-off-by: Dave Chinner

xfs: stop holding ILOCK over filldir callbacks

2015-08-19T00:33:00+00:00

The recent change to the readdir locking made in 40194ec ("xfs:
reinstate the ilock in xfs_readdir") for CXFS directory sanity was
probably the wrong thing to do. Deep in the readdir code we
can take page faults in the filldir callback, and so taking a page
fault while holding an inode ilock creates a new set of locking
issues that lockdep warns all over the place about.

The locking order for regular inodes w.r.t. page faults is io_lock
-> pagefault -> mmap_sem -> ilock. The directory readdir code now
triggers ilock -> page fault -> mmap_sem. While we cannot deadlock
at this point, it inverts all the locking patterns that lockdep
normally sees on XFS inodes, and so triggers lockdep. We worked
around this with commit 93a8614 ("xfs: fix directory inode iolock
lockdep false positive"), but that then just moved the lockdep
warning to deeper in the page fault path and triggered on security
inode locks. Fixing the shmem issue there just moved the lockdep
reports somewhere else, and now we are getting false positives from
filesystem freezing annotations getting confused.

Further, if we enter memory reclaim in a readdir path, we now get
lockdep warning about potential deadlocks because the ilock is held
when we enter reclaim. This, again, is different to a regular file
in that we never allow memory reclaim to run while holding the ilock
for regular files. Hence lockdep now throws
ilock->kmalloc->reclaim->ilock warnings.

Basically, the problem is that the ilock is being used to protect
the directory data and the inode metadata, whereas for a regular
file the iolock protects the data and the ilock protects the
metadata. From the VFS perspective, the i_mutex serialises all
accesses to the directory data, and so not holding the ilock for
readdir doesn't matter. The issue is that CXFS doesn't access
directory data via the VFS, so it has no "data serialisaton"
mechanism. Hence we need to hold the IOLOCK in the correct places to
provide this low level directory data access serialisation.

The ilock can then be used just when the extent list needs to be
read, just like we do for regular files. The directory modification
code can take the iolock exclusive when the ilock is also taken,
and this then ensures that readdir is correct excluded while
modifications are in progress.

Signed-off-by: Dave Chinner 
Reviewed-by: Brian Foster 
Signed-off-by: Dave Chinner

Merge branch 'xfs-misc-fixes-for-3.19-2' into for-next

2014-12-03T22:46:17+00:00

Conflicts:
	fs/xfs/xfs_iops.c

xfs: move ftype conversion functions to libxfs

2014-12-03T22:43:17+00:00

These functions are needed in userspace for repair and mkfs to
do the right thing. Move them to libxfs so they can be easily
shared.

Signed-off-by: Dave Chinner 
Reviewed-by: Christoph Hellwig 
Signed-off-by: Dave Chinner

xfs: move most of xfs_sb.h to xfs_format.h

2014-11-28T03:27:09+00:00

More on-disk format consolidation.

Signed-off-by: Christoph Hellwig 
Reviewed-by: Dave Chinner 
Signed-off-by: Dave Chinner

xfs: merge xfs_ag.h into xfs_format.h

2014-11-28T03:25:04+00:00

More on-disk format consolidation.  A few declarations that weren't on-disk
format related move into better suitable spots.

Signed-off-by: Christoph Hellwig 
Reviewed-by: Dave Chinner 
Signed-off-by: Dave Chinner

xfs: merge xfs_dinode.h into xfs_format.h

2014-11-28T03:24:06+00:00

More consolidatation for the on-disk format defintions.  Note that the
XFS_IS_REALTIME_INODE moves to xfs_linux.h instead as it is not related
to the on disk format, but depends on a CONFIG_ option.

Signed-off-by: Christoph Hellwig 
Reviewed-by: Dave Chinner 
Signed-off-by: Dave Chinner

xfs: global error sign conversion

2014-06-25T04:58:08+00:00

Convert all the errors the core XFs code to negative error signs
like the rest of the kernel and remove all the sign conversion we
do in the interface layers.

Errors for conversion (and comparison) found via searches like:

$ git grep " E" fs/xfs
$ git grep "return E" fs/xfs
$ git grep " E[A-Z].*;$" fs/xfs

Negation points found via searches like:

$ git grep "= -[a-z,A-Z]" fs/xfs
$ git grep "return -[a-z,A-D,F-Z]" fs/xfs
$ git grep " -[a-z].*;" fs/xfs

[ with some bits I missed from Brian Foster ]

Signed-off-by: Dave Chinner 
Reviewed-by: Brian Foster 
Signed-off-by: Dave Chinner