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Filipe Manana 9acc8103ab btrfs: fix unpersisted i_size on fsync after expanding truncate
If we have an inode that does not have the full sync flag set, was changed
in the current transaction, then it is logged while logging some other
inode (like its parent directory for example), its i_size is increased by
a truncate operation, the log is synced through an fsync of some other
inode and then finally we explicitly call fsync on our inode, the new
i_size is not persisted.

The following example shows how to trigger it, with comments explaining
how and why the issue happens:

  $ mkfs.btrfs -f /dev/sdc
  $ mount /dev/sdc /mnt

  $ touch /mnt/foo
  $ xfs_io -f -c "pwrite -S 0xab 0 1M" /mnt/bar

  $ sync

  # Fsync bar, this will be a noop since the file has not yet been
  # modified in the current transaction. The goal here is to clear
  # BTRFS_INODE_NEEDS_FULL_SYNC from the inode's runtime flags.
  $ xfs_io -c "fsync" /mnt/bar

  # Now rename both files, without changing their parent directory.
  $ mv /mnt/bar /mnt/bar2
  $ mv /mnt/foo /mnt/foo2

  # Increase the size of bar2 with a truncate operation.
  $ xfs_io -c "truncate 2M" /mnt/bar2

  # Now fsync foo2, this results in logging its parent inode (the root
  # directory), and logging the parent results in logging the inode of
  # file bar2 (its inode item and the new name). The inode of file bar2
  # is logged with an i_size of 0 bytes since it's logged in
  # LOG_INODE_EXISTS mode, meaning we are only logging its names (and
  # xattrs if it had any) and the i_size of the inode will not be changed
  # when the log is replayed.
  $ xfs_io -c "fsync" /mnt/foo2

  # Now explicitly fsync bar2. This resulted in doing nothing, not
  # logging the inode with the new i_size of 2M and the hole from file
  # offset 1M to 2M. Because the inode did not have the flag
  # BTRFS_INODE_NEEDS_FULL_SYNC set, when it was logged through the
  # fsync of file foo2, its last_log_commit field was updated,
  # resulting in this explicit of file bar2 not doing anything.
  $ xfs_io -c "fsync" /mnt/bar2

  # File bar2 content and size before a power failure.
  $ od -A d -t x1 /mnt/bar2
  0000000 ab ab ab ab ab ab ab ab ab ab ab ab ab ab ab ab
  *
  1048576 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  *
  2097152

  <power failure>

  # Mount the filesystem to replay the log.
  $ mount /dev/sdc /mnt

  # Read the file again, should have the same content and size as before
  # the power failure happened, but it doesn't, i_size is still at 1M.
  $ od -A d -t x1 /mnt/bar2
  0000000 ab ab ab ab ab ab ab ab ab ab ab ab ab ab ab ab
  *
  1048576

This started to happen after commit 209ecbb858 ("btrfs: remove stale
comment and logic from btrfs_inode_in_log()"), since btrfs_inode_in_log()
no longer checks if the inode's list of modified extents is not empty.
However, checking that list is not the right way to address this case
and the check was added long time ago in commit 125c4cf9f3
("Btrfs: set inode's logged_trans/last_log_commit after ranged fsync")
for a different purpose, to address consecutive ranged fsyncs.

The reason that checking for the list emptiness makes this test pass is
because during an expanding truncate we create an extent map to represent
a hole from the old i_size to the new i_size, and add that extent map to
the list of modified extents in the inode. However if we are low on
available memory and we can not allocate a new extent map, then we don't
treat it as an error and just set the full sync flag on the inode, so that
the next fsync does not rely on the list of modified extents - so checking
for the emptiness of the list to decide if the inode needs to be logged is
not reliable, and results in not logging the inode if it was not possible
to allocate the extent map for the hole.

Fix this by ensuring that if we are only logging that an inode exists
(inode item, names/references and xattrs), we don't update the inode's
last_log_commit even if it does not have the full sync runtime flag set.

A test case for fstests follows soon.

CC: stable@vger.kernel.org # 5.13+
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
2021-07-22 15:49:42 +02:00
arch A first set of urgent fixes to the FPU/XSTATE handling mess^W code. 2021-06-20 09:09:58 -07:00
block block-5.13-2021-05-22 2021-05-22 07:40:34 -10:00
certs Kbuild updates for v5.13 (2nd) 2021-05-08 10:00:11 -07:00
crypto async_xor: check src_offs is not NULL before updating it 2021-06-10 19:40:14 -07:00
Documentation RISC-V Fixes for 5.13-rc7 2021-06-19 08:45:34 -07:00
drivers A single fix for GICv3 to not take an interrupt in an NMI context. 2021-06-20 09:38:14 -07:00
fs btrfs: fix unpersisted i_size on fsync after expanding truncate 2021-07-22 15:49:42 +02:00
include btrfs: rip out may_commit_transaction 2021-06-22 14:50:45 +02:00
init pid: take a reference when initializing cad_pid 2021-06-05 08:58:11 -07:00
ipc ipc/mqueue, msg, sem: avoid relying on a stack reference past its expiry 2021-05-22 15:09:07 -10:00
kernel - A single fix to restore fairness between control groups with equal priority 2021-06-20 09:44:52 -07:00
lib lib: crc64: fix kernel-doc warning 2021-06-05 08:58:12 -07:00
LICENSES LICENSES: Add the CC-BY-4.0 license 2020-12-08 10:33:27 -07:00
mm mm/sparse: fix check_usemap_section_nr warnings 2021-06-16 09:24:43 -07:00
net Networking fixes for 5.13-rc7, including fixes from wireless, bpf, 2021-06-18 18:55:29 -07:00
samples VFIO fixes for v5.13-rc5 2021-06-03 11:52:24 -07:00
scripts recordmcount: Correct st_shndx handling 2021-06-18 09:09:17 -04:00
security trusted-keys: match tpm_get_ops on all return paths 2021-05-12 22:36:37 +03:00
sound sound fixes for 5.13-rc6 2021-06-11 10:47:10 -07:00
tools tools headers UAPI: Sync linux/in.h copy with the kernel sources 2021-06-19 10:15:22 -03:00
usr .gitignore: prefix local generated files with a slash 2021-05-02 00:43:35 +09:00
virt KVM: VMX: update vcpu posted-interrupt descriptor when assigning device 2021-05-27 07:58:23 -04:00
.clang-format clang-format: Update with the latest for_each macro list 2021-05-12 23:32:39 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore .gitignore: ignore only top-level modules.builtin 2021-05-02 00:43:35 +09:00
.mailmap mailmap: use private address for Michel Lespinasse 2021-06-05 08:58:12 -07:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: move Murali Karicheri to credits 2021-04-29 15:47:30 -07:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS Networking fixes for 5.13-rc7, including fixes from wireless, bpf, 2021-06-18 18:55:29 -07:00
Makefile Linux 5.13-rc7 2021-06-20 15:03:15 -07:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

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.