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1d0648767c
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Filipe Manana 1d0648767c Btrfs: fix race between block group removal and block group allocation 
[ Upstream commit 8eaf40c0e2 ]

If a task is removing the block group that currently has the highest start
offset amongst all existing block groups, there is a short time window
where it races with a concurrent block group allocation, resulting in a
transaction abort with an error code of EEXIST.

The following diagram explains the race in detail:

      Task A                                                        Task B

 btrfs_remove_block_group(bg offset X)

   remove_extent_mapping(em offset X)
     -> removes extent map X from the
        tree of extent maps
        (fs_info->mapping_tree), so the
        next call to find_next_chunk()
        will return offset X

                                                   btrfs_alloc_chunk()
                                                     find_next_chunk()
                                                       --> returns offset X

                                                     __btrfs_alloc_chunk(offset X)
                                                       btrfs_make_block_group()
                                                         btrfs_create_block_group_cache()
                                                           --> creates btrfs_block_group_cache
                                                               object with a key corresponding
                                                               to the block group item in the
                                                               extent, the key is:
                                                               (offset X, BTRFS_BLOCK_GROUP_ITEM_KEY, 1G)

                                                         --> adds the btrfs_block_group_cache object
                                                             to the list new_bgs of the transaction
                                                             handle

                                                   btrfs_end_transaction(trans handle)
                                                     __btrfs_end_transaction()
                                                       btrfs_create_pending_block_groups()
                                                         --> sees the new btrfs_block_group_cache
                                                             in the new_bgs list of the transaction
                                                             handle
                                                         --> its call to btrfs_insert_item() fails
                                                             with -EEXIST when attempting to insert
                                                             the block group item key
                                                             (offset X, BTRFS_BLOCK_GROUP_ITEM_KEY, 1G)
                                                             because task A has not removed that key yet
                                                         --> aborts the running transaction with
                                                             error -EEXIST

   btrfs_del_item()
     -> removes the block group's key from
        the extent tree, key is
        (offset X, BTRFS_BLOCK_GROUP_ITEM_KEY, 1G)

A sample transaction abort trace:

  [78912.403537] ------------[ cut here ]------------
  [78912.403811] BTRFS: Transaction aborted (error -17)
  [78912.404082] WARNING: CPU: 2 PID: 20465 at fs/btrfs/extent-tree.c:10551 btrfs_create_pending_block_groups+0x196/0x250 [btrfs]
  (...)
  [78912.405642] CPU: 2 PID: 20465 Comm: btrfs Tainted: G        W         5.0.0-btrfs-next-46 #1
  [78912.405941] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.11.2-0-gf9626ccb91-prebuilt.qemu-project.org 04/01/2014
  [78912.406586] RIP: 0010:btrfs_create_pending_block_groups+0x196/0x250 [btrfs]
  (...)
  [78912.407636] RSP: 0018:ffff9d3d4b7e3b08 EFLAGS: 00010282
  [78912.407997] RAX: 0000000000000000 RBX: ffff90959a3796f0 RCX: 0000000000000006
  [78912.408369] RDX: 0000000000000007 RSI: 0000000000000001 RDI: ffff909636b16860
  [78912.408746] RBP: ffff909626758a58 R08: 0000000000000000 R09: 0000000000000000
  [78912.409144] R10: ffff9095ff462400 R11: 0000000000000000 R12: ffff90959a379588
  [78912.409521] R13: ffff909626758ab0 R14: ffff9095036c0000 R15: ffff9095299e1158
  [78912.409899] FS:  00007f387f16f700(0000) GS:ffff909636b00000(0000) knlGS:0000000000000000
  [78912.410285] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
  [78912.410673] CR2: 00007f429fc87cbc CR3: 000000014440a004 CR4: 00000000003606e0
  [78912.411095] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
  [78912.411496] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
  [78912.411898] Call Trace:
  [78912.412318]  __btrfs_end_transaction+0x5b/0x1c0 [btrfs]
  [78912.412746]  btrfs_inc_block_group_ro+0xcf/0x160 [btrfs]
  [78912.413179]  scrub_enumerate_chunks+0x188/0x5b0 [btrfs]
  [78912.413622]  ? __mutex_unlock_slowpath+0x100/0x2a0
  [78912.414078]  btrfs_scrub_dev+0x2ef/0x720 [btrfs]
  [78912.414535]  ? __sb_start_write+0xd4/0x1c0
  [78912.414963]  ? mnt_want_write_file+0x24/0x50
  [78912.415403]  btrfs_ioctl+0x17fb/0x3120 [btrfs]
  [78912.415832]  ? lock_acquire+0xa6/0x190
  [78912.416256]  ? do_vfs_ioctl+0xa2/0x6f0
  [78912.416685]  ? btrfs_ioctl_get_supported_features+0x30/0x30 [btrfs]
  [78912.417116]  do_vfs_ioctl+0xa2/0x6f0
  [78912.417534]  ? __fget+0x113/0x200
  [78912.417954]  ksys_ioctl+0x70/0x80
  [78912.418369]  __x64_sys_ioctl+0x16/0x20
  [78912.418812]  do_syscall_64+0x60/0x1b0
  [78912.419231]  entry_SYSCALL_64_after_hwframe+0x49/0xbe
  [78912.419644] RIP: 0033:0x7f3880252dd7
  (...)
  [78912.420957] RSP: 002b:00007f387f16ed68 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
  [78912.421426] RAX: ffffffffffffffda RBX: 000055f5becc1df0 RCX: 00007f3880252dd7
  [78912.421889] RDX: 000055f5becc1df0 RSI: 00000000c400941b RDI: 0000000000000003
  [78912.422354] RBP: 0000000000000000 R08: 00007f387f16f700 R09: 0000000000000000
  [78912.422790] R10: 00007f387f16f700 R11: 0000000000000246 R12: 0000000000000000
  [78912.423202] R13: 00007ffda49c266f R14: 0000000000000000 R15: 00007f388145e040
  [78912.425505] ---[ end trace eb9bfe7c426fc4d3 ]---

Fix this by calling remove_extent_mapping(), at btrfs_remove_block_group(),
only at the very end, after removing the block group item key from the
extent tree (and removing the free space tree entry if we are using the
free space tree feature).

Fixes: 04216820fe ("Btrfs: fix race between fs trimming and block group remove/allocation")
CC: stable@vger.kernel.org # 4.4+
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
2019-09-16 08:22:15 +02:00
arch kvm: Check irqchip mode before assign irqfd 2019-09-16 08:22:15 +02:00
block blk-mq: free hw queue's resource in hctx's release handler 2019-09-16 08:22:13 +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 dt-bindings: mmc: Add disable-cqe-dcmd property. 2019-09-16 08:22:12 +02:00
drivers drm/amdgpu/{uvd,vcn}: fetch ring's read_ptr after alloc 2019-09-16 08:22:15 +02:00
firmware kbuild: remove all dummy assignments to obj- 2017-11-18 11:46:06 +09:00
fs Btrfs: fix race between block group removal and block group allocation 2019-09-16 08:22:15 +02:00
include dm mpath: fix missing call of path selector type->end_io 2019-09-16 08:22:12 +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 kernel/module: Fix mem leak in module_add_modinfo_attrs 2019-09-16 08:21:45 +02:00
lib lib: logic_pio: Add logic_pio_unregister_range() 2019-09-06 10:22:19 +02:00
LICENSES LICENSES: Remove CC-BY-SA-4.0 license text 2018-10-18 11:28:50 +02:00
mm mm/zsmalloc.c: fix build when CONFIG_COMPACTION=n 2019-09-06 10:22:08 +02:00
net {nl,mac}80211: fix interface combinations on crypto controlled devices 2019-09-16 08:21:42 +02:00
samples samples, bpf: suppress compiler warning 2019-07-14 08:11:04 +02:00
scripts scripts/decode_stacktrace: match basepath using shell prefix operator, not regex 2019-09-16 08:21:44 +02:00
security selinux: fix memory leak in policydb_init() 2019-08-06 19:06:54 +02:00
sound ALSA: hda/realtek - Fix the problem of two front mics on a ThinkCentre 2019-09-16 08:21:40 +02:00
tools selftests: fib_rule_tests: use pre-defined DEV_ADDR 2019-09-16 08:21:42 +02:00
usr initramfs: move gen_initramfs_list.sh from scripts/ to usr/ 2018-08-22 23:21:44 +09:00
virt kvm: Check irqchip mode before assign irqfd 2019-09-16 08:22:15 +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 4.19.72 2019-09-10 10:33:54 +01:00
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.