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Su Yue c41ec4529d btrfs: fix lockdep warning due to seqcount_mutex on 32bit arch 
This effectively reverts commit d5c8238849 ("btrfs: convert
data_seqcount to seqcount_mutex_t").

While running fstests on 32 bits test box, many tests failed because of
warnings in dmesg. One of those warnings (btrfs/003):

  [66.441317] WARNING: CPU: 6 PID: 9251 at include/linux/seqlock.h:279 btrfs_remove_chunk+0x58b/0x7b0 [btrfs]
  [66.441446] CPU: 6 PID: 9251 Comm: btrfs Tainted: G           O      5.11.0-rc4-custom+ #5
  [66.441449] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS ArchLinux 1.14.0-1 04/01/2014
  [66.441451] EIP: btrfs_remove_chunk+0x58b/0x7b0 [btrfs]
  [66.441472] EAX: 00000000 EBX: 00000001 ECX: c576070c EDX: c6b15803
  [66.441475] ESI: 10000000 EDI: 00000000 EBP: c56fbcfc ESP: c56fbc70
  [66.441477] DS: 007b ES: 007b FS: 00d8 GS: 00e0 SS: 0068 EFLAGS: 00010246
  [66.441481] CR0: 80050033 CR2: 05c8da20 CR3: 04b20000 CR4: 00350ed0
  [66.441485] Call Trace:
  [66.441510]  btrfs_relocate_chunk+0xb1/0x100 [btrfs]
  [66.441529]  ? btrfs_lookup_block_group+0x17/0x20 [btrfs]
  [66.441562]  btrfs_balance+0x8ed/0x13b0 [btrfs]
  [66.441586]  ? btrfs_ioctl_balance+0x333/0x3c0 [btrfs]
  [66.441619]  ? __this_cpu_preempt_check+0xf/0x11
  [66.441643]  btrfs_ioctl_balance+0x333/0x3c0 [btrfs]
  [66.441664]  ? btrfs_ioctl_get_supported_features+0x30/0x30 [btrfs]
  [66.441683]  btrfs_ioctl+0x414/0x2ae0 [btrfs]
  [66.441700]  ? __lock_acquire+0x35f/0x2650
  [66.441717]  ? lockdep_hardirqs_on+0x87/0x120
  [66.441720]  ? lockdep_hardirqs_on_prepare+0xd0/0x1e0
  [66.441724]  ? call_rcu+0x2d3/0x530
  [66.441731]  ? __might_fault+0x41/0x90
  [66.441736]  ? kvm_sched_clock_read+0x15/0x50
  [66.441740]  ? sched_clock+0x8/0x10
  [66.441745]  ? sched_clock_cpu+0x13/0x180
  [66.441750]  ? btrfs_ioctl_get_supported_features+0x30/0x30 [btrfs]
  [66.441750]  ? btrfs_ioctl_get_supported_features+0x30/0x30 [btrfs]
  [66.441768]  __ia32_sys_ioctl+0x165/0x8a0
  [66.441773]  ? __this_cpu_preempt_check+0xf/0x11
  [66.441785]  ? __might_fault+0x89/0x90
  [66.441791]  __do_fast_syscall_32+0x54/0x80
  [66.441796]  do_fast_syscall_32+0x32/0x70
  [66.441801]  do_SYSENTER_32+0x15/0x20
  [66.441805]  entry_SYSENTER_32+0x9f/0xf2
  [66.441808] EIP: 0xab7b5549
  [66.441814] EAX: ffffffda EBX: 00000003 ECX: c4009420 EDX: bfa91f5c
  [66.441816] ESI: 00000003 EDI: 00000001 EBP: 00000000 ESP: bfa91e98
  [66.441818] DS: 007b ES: 007b FS: 0000 GS: 0033 SS: 007b EFLAGS: 00000292
  [66.441833] irq event stamp: 42579
  [66.441835] hardirqs last  enabled at (42585): [<c60eb065>] console_unlock+0x495/0x590
  [66.441838] hardirqs last disabled at (42590): [<c60eafd5>] console_unlock+0x405/0x590
  [66.441840] softirqs last  enabled at (41698): [<c601b76c>] call_on_stack+0x1c/0x60
  [66.441843] softirqs last disabled at (41681): [<c601b76c>] call_on_stack+0x1c/0x60

  ========================================================================
  btrfs_remove_chunk+0x58b/0x7b0:
  __seqprop_mutex_assert at linux/./include/linux/seqlock.h:279
  (inlined by) btrfs_device_set_bytes_used at linux/fs/btrfs/volumes.h:212
  (inlined by) btrfs_remove_chunk at linux/fs/btrfs/volumes.c:2994
  ========================================================================

The warning is produced by lockdep_assert_held() in
__seqprop_mutex_assert() if CONFIG_LOCKDEP is enabled.
And "olumes.c:2994 is btrfs_device_set_bytes_used() with mutex lock
fs_info->chunk_mutex held already.

After adding some debug prints, the cause was found that many
__alloc_device() are called with NULL @fs_info (during scanning ioctl).
Inside the function, btrfs_device_data_ordered_init() is expanded to
seqcount_mutex_init().  In this scenario, its second
parameter info->chunk_mutex  is &NULL->chunk_mutex which equals
to offsetof(struct btrfs_fs_info, chunk_mutex) unexpectedly. Thus,
seqcount_mutex_init() is called in wrong way. And later
btrfs_device_get/set helpers trigger lockdep warnings.

The device and filesystem object lifetimes are different and we'd have
to synchronize initialization of the btrfs_device::data_seqcount with
the fs_info, possibly using some additional synchronization. It would
still not prevent concurrent access to the seqcount lock when it's used
for read and initialization.

Commit d5c8238849 ("btrfs: convert data_seqcount to seqcount_mutex_t")
does not mention a particular problem being fixed so revert should not
cause any harm and we'll get the lockdep warning fixed.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=210139
Reported-by: Erhard F <erhard_f@mailbox.org>
Fixes: d5c8238849 ("btrfs: convert data_seqcount to seqcount_mutex_t")
CC: stable@vger.kernel.org # 5.10
CC: Davidlohr Bueso <dbueso@suse.de>
Signed-off-by: Su Yue <l@damenly.su>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
2021-01-25 18:44:50 +01:00
arch USB fixes for 5.10-rc7 2020-12-06 11:38:36 -08:00
block block-5.10-2020-12-05 2020-12-05 14:45:30 -08:00
certs .gitignore: add SPDX License Identifier 2020-03-25 11:50:48 +01:00
crypto drivers-5.10-2020-10-12 2020-10-13 13:04:41 -07:00
Documentation Networking fixes for 5.10-rc7, including fixes from bpf, netfilter, 2020-12-03 13:10:11 -08:00
drivers Char/Misc driver fixes for 5.10-rc7 2020-12-06 11:48:17 -08:00
fs btrfs: fix lockdep warning due to seqcount_mutex on 32bit arch 2021-01-25 18:44:50 +01:00
include btrfs: calculate inline extent buffer page size based on page size 2020-12-09 19:16:10 +01:00
init Kbuild fixes for v5.10 (2nd) 2020-12-06 10:31:39 -08:00
ipc ipc: adjust proc_ipc_sem_dointvec definition to match prototype 2020-09-05 12:14:29 -07:00
kernel A set of updates for the interrupt subsystem: 2020-12-06 11:15:55 -08:00
lib zlib: export S390 symbols for zlib modules 2020-12-06 10:19:07 -08:00
LICENSES LICENSES/deprecated: add Zlib license text 2020-09-16 14:33:49 +02:00
mm mm/mmap.c: fix mmap return value when vma is merged after call_mmap() 2020-12-06 10:19:07 -08:00
net net/sched: act_mpls: ensure LSE is pullable before reading it 2020-12-03 11:13:37 -08:00
samples Tracing fixes for 5.10-rc6 2020-12-01 15:30:18 -08:00
scripts Kbuild fixes for v5.10 (2nd) 2020-12-06 10:31:39 -08:00
security selinux/stable-5.10 PR 20201113 2020-11-14 12:04:02 -08:00
sound ALSA: hda/realtek: Add mute LED quirk to yet another HP x360 model 2020-11-28 10:00:51 +01:00
tools A set of fixes for x86: 2020-12-06 11:22:39 -08:00
usr Merge branch 'work.fdpic' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2020-08-07 13:29:39 -07:00
virt kvm: x86/mmu: Support dirty logging for the TDP MMU 2020-10-23 03:42:13 -04:00
.clang-format RDMA 5.10 pull request 2020-10-17 11:18:18 -07:00
.cocciconfig
.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: docs: ignore sphinx_*/ directories 2020-09-10 10:44:31 -06:00
.mailmap mailmap: add two more addresses of Uwe Kleine-König 2020-12-06 10:19:07 -08:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Move Jason Cooper to CREDITS 2020-11-30 10:20:34 +01:00
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 A set of updates for the interrupt subsystem: 2020-12-06 11:15:55 -08:00
Makefile Linux 5.10-rc7 2020-12-06 14:25:12 -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.