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Filipe Manana 0388d45afc Btrfs: do not start a transaction during fiemap 
commit 03628cdbc6 upstream.

During fiemap, for regular extents (non inline) we need to check if they
are shared and if they are, set the shared bit. Checking if an extent is
shared requires checking the delayed references of the currently running
transaction, since some reference might have not yet hit the extent tree
and be only in the in-memory delayed references.

However we were using a transaction join for this, which creates a new
transaction when there is no transaction currently running. That means
that two more potential failures can happen: creating the transaction and
committing it. Further, if no write activity is currently happening in the
system, and fiemap calls keep being done, we end up creating and
committing transactions that do nothing.

In some extreme cases this can result in the commit of the transaction
created by fiemap to fail with ENOSPC when updating the root item of a
subvolume tree because a join does not reserve any space, leading to a
trace like the following:

 heisenberg kernel: ------------[ cut here ]------------
 heisenberg kernel: BTRFS: Transaction aborted (error -28)
 heisenberg kernel: WARNING: CPU: 0 PID: 7137 at fs/btrfs/root-tree.c:136 btrfs_update_root+0x22b/0x320 [btrfs]
(...)
 heisenberg kernel: CPU: 0 PID: 7137 Comm: btrfs-transacti Not tainted 4.19.0-4-amd64 #1 Debian 4.19.28-2
 heisenberg kernel: Hardware name: FUJITSU LIFEBOOK U757/FJNB2A5, BIOS Version 1.21 03/19/2018
 heisenberg kernel: RIP: 0010:btrfs_update_root+0x22b/0x320 [btrfs]
(...)
 heisenberg kernel: RSP: 0018:ffffb5448828bd40 EFLAGS: 00010286
 heisenberg kernel: RAX: 0000000000000000 RBX: ffff8ed56bccef50 RCX: 0000000000000006
 heisenberg kernel: RDX: 0000000000000007 RSI: 0000000000000092 RDI: ffff8ed6bda166a0
 heisenberg kernel: RBP: 00000000ffffffe4 R08: 00000000000003df R09: 0000000000000007
 heisenberg kernel: R10: 0000000000000000 R11: 0000000000000001 R12: ffff8ed63396a078
 heisenberg kernel: R13: ffff8ed092d7c800 R14: ffff8ed64f5db028 R15: ffff8ed6bd03d068
 heisenberg kernel: FS:  0000000000000000(0000) GS:ffff8ed6bda00000(0000) knlGS:0000000000000000
 heisenberg kernel: CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
 heisenberg kernel: CR2: 00007f46f75f8000 CR3: 0000000310a0a002 CR4: 00000000003606f0
 heisenberg kernel: DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
 heisenberg kernel: DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
 heisenberg kernel: Call Trace:
 heisenberg kernel:  commit_fs_roots+0x166/0x1d0 [btrfs]
 heisenberg kernel:  ? _cond_resched+0x15/0x30
 heisenberg kernel:  ? btrfs_run_delayed_refs+0xac/0x180 [btrfs]
 heisenberg kernel:  btrfs_commit_transaction+0x2bd/0x870 [btrfs]
 heisenberg kernel:  ? start_transaction+0x9d/0x3f0 [btrfs]
 heisenberg kernel:  transaction_kthread+0x147/0x180 [btrfs]
 heisenberg kernel:  ? btrfs_cleanup_transaction+0x530/0x530 [btrfs]
 heisenberg kernel:  kthread+0x112/0x130
 heisenberg kernel:  ? kthread_bind+0x30/0x30
 heisenberg kernel:  ret_from_fork+0x35/0x40
 heisenberg kernel: ---[ end trace 05de912e30e012d9 ]---

Since fiemap (and btrfs_check_shared()) is a read-only operation, do not do
a transaction join to avoid the overhead of creating a new transaction (if
there is currently no running transaction) and introducing a potential
point of failure when the new transaction gets committed, instead use a
transaction attach to grab a handle for the currently running transaction
if any.

Reported-by: Christoph Anton Mitterer <calestyo@scientia.net>
Link: https://lore.kernel.org/linux-btrfs/b2a668d7124f1d3e410367f587926f622b3f03a4.camel@scientia.net/
Fixes: afce772e87 ("btrfs: fix check_shared for fiemap ioctl")
CC: stable@vger.kernel.org # 4.14+
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2019-05-22 07:37:43 +02:00
arch bpf, arm64: remove prefetch insn in xadd mapping 2019-05-22 07:37:38 +02:00
block bfq: update internal depth state when queue depth changes 2019-05-16 19:41:17 +02:00
certs export.h: remove VMLINUX_SYMBOL() and VMLINUX_SYMBOL_STR() 2018-08-22 23:21:44 +09:00
crypto crypto: gcm - fix incompatibility between "gcm" and "gcm_base" 2019-05-22 07:37:37 +02:00
Documentation x86/speculation/mds: Improve CPU buffer clear documentation 2019-05-22 07:37:35 +02:00
drivers tty/vt: fix write/write race in ioctl(KDSKBSENT) handler 2019-05-22 07:37:41 +02:00
firmware kbuild: remove all dummy assignments to obj- 2017-11-18 11:46:06 +09:00
fs Btrfs: do not start a transaction during fiemap 2019-05-22 07:37:43 +02:00
include mfd: max77620: Fix swapped FPS_PERIOD_MAX_US values 2019-05-22 07:37:41 +02:00
init init: initialize jump labels before command line option parsing 2019-05-16 19:41:23 +02:00
ipc ipc/shm.c: use ERR_CAST() for shm_lock() error return 2018-10-05 16:32:04 -07:00
kernel userfaultfd: use RCU to free the task struct when fork fails 2019-05-22 07:37:41 +02:00
lib ubsan: Fix nasty -Wbuiltin-declaration-mismatch GCC-9 warnings 2019-05-10 17:54:04 +02:00
LICENSES LICENSES: Remove CC-BY-SA-4.0 license text 2018-10-18 11:28:50 +02:00
mm hugetlb: use same fault hash key for shared and private mappings 2019-05-22 07:37:40 +02:00
net tipc: fix hanging clients using poll with EPOLLOUT flag 2019-05-16 19:41:31 +02:00
samples samples: mei: use /dev/mei0 instead of /dev/mei 2019-02-15 08:10:11 +01:00
scripts fs: stream_open - opener for stream-like files so that read and write can run simultaneously without deadlock 2019-05-08 07:21:51 +02:00
security selinux: do not report error on connect(AF_UNSPEC) 2019-05-16 19:41:30 +02:00
sound ASoC: codec: hdac_hdmi add device_link to card device 2019-05-22 07:37:38 +02:00
tools objtool: Fix function fallthrough detection 2019-05-22 07:37:35 +02:00
usr initramfs: move gen_initramfs_list.sh from scripts/ to usr/ 2018-08-22 23:21:44 +09:00
virt KVM: fix spectrev1 gadgets 2019-05-16 19:41:22 +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 4.19.44 2019-05-16 19:41:32 +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.