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Filipe Manana 8e92821878 Btrfs: fix corruption reading shared and compressed extents after hole punching 
In the past we had data corruption when reading compressed extents that
are shared within the same file and they are consecutive, this got fixed
by commit 005efedf2c ("Btrfs: fix read corruption of compressed and
shared extents") and by commit 808f80b467 ("Btrfs: update fix for read
corruption of compressed and shared extents"). However there was a case
that was missing in those fixes, which is when the shared and compressed
extents are referenced with a non-zero offset. The following shell script
creates a reproducer for this issue:

  #!/bin/bash

  mkfs.btrfs -f /dev/sdc &> /dev/null
  mount -o compress /dev/sdc /mnt/sdc

  # Create a file with 3 consecutive compressed extents, each has an
  # uncompressed size of 128Kb and a compressed size of 4Kb.
  for ((i = 1; i <= 3; i++)); do
      head -c 4096 /dev/zero
      for ((j = 1; j <= 31; j++)); do
          head -c 4096 /dev/zero | tr '\0' "\377"
      done
  done > /mnt/sdc/foobar
  sync

  echo "Digest after file creation:   $(md5sum /mnt/sdc/foobar)"

  # Clone the first extent into offsets 128K and 256K.
  xfs_io -c "reflink /mnt/sdc/foobar 0 128K 128K" /mnt/sdc/foobar
  xfs_io -c "reflink /mnt/sdc/foobar 0 256K 128K" /mnt/sdc/foobar
  sync

  echo "Digest after cloning:         $(md5sum /mnt/sdc/foobar)"

  # Punch holes into the regions that are already full of zeroes.
  xfs_io -c "fpunch 0 4K" /mnt/sdc/foobar
  xfs_io -c "fpunch 128K 4K" /mnt/sdc/foobar
  xfs_io -c "fpunch 256K 4K" /mnt/sdc/foobar
  sync

  echo "Digest after hole punching:   $(md5sum /mnt/sdc/foobar)"

  echo "Dropping page cache..."
  sysctl -q vm.drop_caches=1
  echo "Digest after hole punching:   $(md5sum /mnt/sdc/foobar)"

  umount /dev/sdc

When running the script we get the following output:

  Digest after file creation:   5a0888d80d7ab1fd31c229f83a3bbcc8  /mnt/sdc/foobar
  linked 131072/131072 bytes at offset 131072
  128 KiB, 1 ops; 0.0033 sec (36.960 MiB/sec and 295.6830 ops/sec)
  linked 131072/131072 bytes at offset 262144
  128 KiB, 1 ops; 0.0015 sec (78.567 MiB/sec and 628.5355 ops/sec)
  Digest after cloning:         5a0888d80d7ab1fd31c229f83a3bbcc8  /mnt/sdc/foobar
  Digest after hole punching:   5a0888d80d7ab1fd31c229f83a3bbcc8  /mnt/sdc/foobar
  Dropping page cache...
  Digest after hole punching:   fba694ae8664ed0c2e9ff8937e7f1484  /mnt/sdc/foobar

This happens because after reading all the pages of the extent in the
range from 128K to 256K for example, we read the hole at offset 256K
and then when reading the page at offset 260K we don't submit the
existing bio, which is responsible for filling all the page in the
range 128K to 256K only, therefore adding the pages from range 260K
to 384K to the existing bio and submitting it after iterating over the
entire range. Once the bio completes, the uncompressed data fills only
the pages in the range 128K to 256K because there's no more data read
from disk, leaving the pages in the range 260K to 384K unfilled. It is
just a slightly different variant of what was solved by commit
005efedf2c ("Btrfs: fix read corruption of compressed and shared
extents").

Fix this by forcing a bio submit, during readpages(), whenever we find a
compressed extent map for a page that is different from the extent map
for the previous page or has a different starting offset (in case it's
the same compressed extent), instead of the extent map's original start
offset.

A test case for fstests follows soon.

Reported-by: Zygo Blaxell <ce3g8jdj@umail.furryterror.org>
Fixes: 808f80b467 ("Btrfs: update fix for read corruption of compressed and shared extents")
Fixes: 005efedf2c ("Btrfs: fix read corruption of compressed and shared extents")
Cc: stable@vger.kernel.org # 4.3+
Tested-by: Zygo Blaxell <ce3g8jdj@umail.furryterror.org>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
2019-02-27 12:24:07 +01:00
arch Bug fixes. 2019-02-24 09:47:07 -08:00
block for-linus-20190215 2019-02-15 09:12:28 -08:00
certs kbuild: remove redundant target cleaning on failure 2019-01-06 09:46:51 +09:00
crypto net: crypto set sk to NULL when af_alg_release. 2019-02-18 12:01:24 -08:00
Documentation Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2019-02-24 09:28:26 -08:00
drivers Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2019-02-24 09:28:26 -08:00
firmware kbuild: change filechk to surround the given command with { } 2019-01-06 09:46:51 +09:00
fs Btrfs: fix corruption reading shared and compressed extents after hole punching 2019-02-27 12:24:07 +01:00
include btrfs: qgroup: Move reserved data accounting from btrfs_delayed_ref_head to btrfs_qgroup_extent_record 2019-02-25 14:13:39 +01:00
init revert "initramfs: cleanup incomplete rootfs" 2019-02-21 09:00:59 -08:00
ipc ipc: IPCMNI limit check for semmni 2018-10-31 08:54:14 -07:00
kernel Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2019-02-24 09:28:26 -08:00
lib Merge branch 'fixes-v5.1-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security 2019-02-20 09:09:33 -08:00
LICENSES This is a fairly typical cycle for documentation. There's some welcome 2018-10-24 18:01:11 +01:00
mm mm, memory_hotplug: fix off-by-one in is_pageblock_removable 2019-02-21 09:01:01 -08:00
net Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2019-02-24 09:28:26 -08:00
samples samples: mei: use /dev/mei0 instead of /dev/mei 2019-01-30 15:24:45 +01:00
scripts kallsyms: Handle too long symbols in kallsyms.c 2019-01-28 13:02:09 +09:00
security Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2019-02-24 09:28:26 -08:00
sound sound fixes for 5.0 2019-02-20 09:42:52 -08:00
tools selftests: fib_tests: sleep after changing carrier. again. 2019-02-23 18:34:20 -08:00
usr user/Makefile: Fix typo and capitalization in comment section 2018-12-11 00:18:03 +09:00
virt KVM/ARM fixes for 5.0: 2019-02-13 19:39:24 +01:00
.clang-format clang-format: Update .clang-format with the latest for_each macro list 2019-01-19 19:26:06 +01:00
.cocciconfig
.get_maintainer.ignore
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore kbuild: Add support for DT binding schema checks 2018-12-13 09:41:32 -06:00
.mailmap A few early MIPS fixes for 4.21: 2019-01-05 12:48:25 -08:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS CREDITS/MAINTAINERS: Retire parisc-linux.org email domain 2019-02-21 20:16:10 +01:00
Kbuild kbuild: use assignment instead of define ... endef for filechk_* rules 2019-01-06 10:22:35 +09:00
Kconfig kconfig: move the "Executable file formats" menu to fs/Kconfig.binfmt 2018-08-02 08:06:55 +09:00
MAINTAINERS Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2019-02-24 09:28:26 -08:00
Makefile Linux 5.0-rc8 2019-02-24 16:46:45 -08:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

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.