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Filipe Manana f833deae2a Btrfs: fix deadlock between fiemap and transaction commits 
[ Upstream commit a6d155d2e3 ]

The fiemap handler locks a file range that can have unflushed delalloc,
and after locking the range, it tries to attach to a running transaction.
If the running transaction started its commit, that is, it is in state
TRANS_STATE_COMMIT_START, and either the filesystem was mounted with the
flushoncommit option or the transaction is creating a snapshot for the
subvolume that contains the file that fiemap is operating on, we end up
deadlocking. This happens because fiemap is blocked on the transaction,
waiting for it to complete, and the transaction is waiting for the flushed
dealloc to complete, which requires locking the file range that the fiemap
task already locked. The following stack traces serve as an example of
when this deadlock happens:

  (...)
  [404571.515510] Workqueue: btrfs-endio-write btrfs_endio_write_helper [btrfs]
  [404571.515956] Call Trace:
  [404571.516360]  ? __schedule+0x3ae/0x7b0
  [404571.516730]  schedule+0x3a/0xb0
  [404571.517104]  lock_extent_bits+0x1ec/0x2a0 [btrfs]
  [404571.517465]  ? remove_wait_queue+0x60/0x60
  [404571.517832]  btrfs_finish_ordered_io+0x292/0x800 [btrfs]
  [404571.518202]  normal_work_helper+0xea/0x530 [btrfs]
  [404571.518566]  process_one_work+0x21e/0x5c0
  [404571.518990]  worker_thread+0x4f/0x3b0
  [404571.519413]  ? process_one_work+0x5c0/0x5c0
  [404571.519829]  kthread+0x103/0x140
  [404571.520191]  ? kthread_create_worker_on_cpu+0x70/0x70
  [404571.520565]  ret_from_fork+0x3a/0x50
  [404571.520915] kworker/u8:6    D    0 31651      2 0x80004000
  [404571.521290] Workqueue: btrfs-flush_delalloc btrfs_flush_delalloc_helper [btrfs]
  (...)
  [404571.537000] fsstress        D    0 13117  13115 0x00004000
  [404571.537263] Call Trace:
  [404571.537524]  ? __schedule+0x3ae/0x7b0
  [404571.537788]  schedule+0x3a/0xb0
  [404571.538066]  wait_current_trans+0xc8/0x100 [btrfs]
  [404571.538349]  ? remove_wait_queue+0x60/0x60
  [404571.538680]  start_transaction+0x33c/0x500 [btrfs]
  [404571.539076]  btrfs_check_shared+0xa3/0x1f0 [btrfs]
  [404571.539513]  ? extent_fiemap+0x2ce/0x650 [btrfs]
  [404571.539866]  extent_fiemap+0x2ce/0x650 [btrfs]
  [404571.540170]  do_vfs_ioctl+0x526/0x6f0
  [404571.540436]  ksys_ioctl+0x70/0x80
  [404571.540734]  __x64_sys_ioctl+0x16/0x20
  [404571.540997]  do_syscall_64+0x60/0x1d0
  [404571.541279]  entry_SYSCALL_64_after_hwframe+0x49/0xbe
  (...)
  [404571.543729] btrfs           D    0 14210  14208 0x00004000
  [404571.544023] Call Trace:
  [404571.544275]  ? __schedule+0x3ae/0x7b0
  [404571.544526]  ? wait_for_completion+0x112/0x1a0
  [404571.544795]  schedule+0x3a/0xb0
  [404571.545064]  schedule_timeout+0x1ff/0x390
  [404571.545351]  ? lock_acquire+0xa6/0x190
  [404571.545638]  ? wait_for_completion+0x49/0x1a0
  [404571.545890]  ? wait_for_completion+0x112/0x1a0
  [404571.546228]  wait_for_completion+0x131/0x1a0
  [404571.546503]  ? wake_up_q+0x70/0x70
  [404571.546775]  btrfs_wait_ordered_extents+0x27c/0x400 [btrfs]
  [404571.547159]  btrfs_commit_transaction+0x3b0/0xae0 [btrfs]
  [404571.547449]  ? btrfs_mksubvol+0x4a4/0x640 [btrfs]
  [404571.547703]  ? remove_wait_queue+0x60/0x60
  [404571.547969]  btrfs_mksubvol+0x605/0x640 [btrfs]
  [404571.548226]  ? __sb_start_write+0xd4/0x1c0
  [404571.548512]  ? mnt_want_write_file+0x24/0x50
  [404571.548789]  btrfs_ioctl_snap_create_transid+0x169/0x1a0 [btrfs]
  [404571.549048]  btrfs_ioctl_snap_create_v2+0x11d/0x170 [btrfs]
  [404571.549307]  btrfs_ioctl+0x133f/0x3150 [btrfs]
  [404571.549549]  ? mem_cgroup_charge_statistics+0x4c/0xd0
  [404571.549792]  ? mem_cgroup_commit_charge+0x84/0x4b0
  [404571.550064]  ? __handle_mm_fault+0xe3e/0x11f0
  [404571.550306]  ? do_raw_spin_unlock+0x49/0xc0
  [404571.550608]  ? _raw_spin_unlock+0x24/0x30
  [404571.550976]  ? __handle_mm_fault+0xedf/0x11f0
  [404571.551319]  ? do_vfs_ioctl+0xa2/0x6f0
  [404571.551659]  ? btrfs_ioctl_get_supported_features+0x30/0x30 [btrfs]
  [404571.552087]  do_vfs_ioctl+0xa2/0x6f0
  [404571.552355]  ksys_ioctl+0x70/0x80
  [404571.552621]  __x64_sys_ioctl+0x16/0x20
  [404571.552864]  do_syscall_64+0x60/0x1d0
  [404571.553104]  entry_SYSCALL_64_after_hwframe+0x49/0xbe
  (...)

If we were joining the transaction instead of attaching to it, we would
not risk a deadlock because a join only blocks if the transaction is in a
state greater then or equals to TRANS_STATE_COMMIT_DOING, and the delalloc
flush performed by a transaction is done before it reaches that state,
when it is in the state TRANS_STATE_COMMIT_START. However a transaction
join is intended for use cases where we do modify the filesystem, and
fiemap only needs to peek at delayed references from the current
transaction in order to determine if extents are shared, and, besides
that, when there is no current transaction or when it blocks to wait for
a current committing transaction to complete, it creates a new transaction
without reserving any space. Such unnecessary transactions, besides doing
unnecessary IO, can cause transaction aborts (-ENOSPC) and unnecessary
rotation of the precious backup roots.

So fix this by adding a new transaction join variant, named join_nostart,
which behaves like the regular join, but it does not create a transaction
when none currently exists or after waiting for a committing transaction
to complete.

Fixes: 03628cdbc6 ("Btrfs: do not start a transaction during fiemap")
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
2019-08-25 10:47:54 +02:00
arch riscv: Make __fstate_clean() work correctly. 2019-08-25 10:47:51 +02:00
block block, scsi: Change the preempt-only flag into a counter 2019-08-04 09:30:57 +02:00
certs export.h: remove VMLINUX_SYMBOL() and VMLINUX_SYMBOL_STR() 2018-08-22 23:21:44 +09:00
crypto crypto: chacha20poly1305 - fix atomic sleep when using async algorithm 2019-07-26 09:14:19 +02:00
Documentation Documentation: Add swapgs description to the Spectre v1 documentation 2019-08-06 19:06:58 +02:00
drivers drm/bridge: lvds-encoder: Fix build error while CONFIG_DRM_KMS_HELPER=m 2019-08-25 10:47:54 +02:00
firmware kbuild: remove all dummy assignments to obj- 2017-11-18 11:46:06 +09:00
fs Btrfs: fix deadlock between fiemap and transaction commits 2019-08-25 10:47:54 +02:00
include KVM: Fix leak vCPU's VMCS value into other pCPU 2019-08-16 10:12:53 +02:00
init initramfs: free initrd memory if opening /initrd.image fails 2019-06-15 11:54:01 +02:00
ipc ipc/mqueue.c: only perform resource calculation if user valid 2019-08-06 19:06:52 +02:00
kernel cpufreq: schedutil: Don't skip freq update when limits change 2019-08-25 10:47:46 +02:00
lib test_firmware: fix a memory leak bug 2019-08-16 10:12:49 +02:00
LICENSES LICENSES: Remove CC-BY-SA-4.0 license text 2018-10-18 11:28:50 +02:00
mm mm/usercopy: use memory range to be accessed for wraparound check 2019-08-25 10:47:44 +02:00
net netfilter: ebtables: also count base chain policies 2019-08-25 10:47:50 +02:00
samples samples, bpf: suppress compiler warning 2019-07-14 08:11:04 +02:00
scripts scripts/sphinx-pre-install: fix script for RHEL/CentOS 2019-08-16 10:12:44 +02:00
security selinux: fix memory leak in policydb_init() 2019-08-06 19:06:54 +02:00
sound ALSA: hda - Let all conexant codec enter D3 when rebooting 2019-08-25 10:47:48 +02:00
tools perf header: Fix use of unitialized value warning 2019-08-25 10:47:53 +02:00
usr initramfs: move gen_initramfs_list.sh from scripts/ to usr/ 2018-08-22 23:21:44 +09:00
virt KVM: Fix leak vCPU's VMCS value into other pCPU 2019-08-16 10:12:53 +02:00
.clang-format clang-format: Set IndentWrappedFunctionNames false 2018-08-01 18:38:51 +02:00
.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 updates for v4.17 (2nd) 2018-04-15 17:21:30 -07:00
.mailmap libnvdimm-for-4.19_misc 2018-08-25 18:13:10 -07:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS 9p: remove Ron Minnich from MAINTAINERS 2018-08-17 16:20:26 -07:00
Kbuild Kbuild updates for v4.15 2017-11-17 17:45:29 -08:00
Kconfig kconfig: move the "Executable file formats" menu to fs/Kconfig.binfmt 2018-08-02 08:06:55 +09:00
MAINTAINERS platform/x86: Add Intel AtomISP2 dummy / power-management driver 2019-04-20 09:16:02 +02:00
Makefile Linux 4.19.67 2019-08-16 10:12:54 +02:00
README Docs: Added a pointer to the formatted docs to README 2018-03-21 09:02:53 -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.
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.