On Fri 22 Jan 2021 at 01:07, David Sterba <dsterba@xxxxxxx> wrote:
Adding Davidlohr to CC as it's about reverting his patch.
In d5c8238849e7 ("btrfs: convert data_seqcount to
seqcount_mutex_t")
the seqcount_mutex_t was added as an annotation for lockep so by
revert
we'd lose that again.
On Thu, Jan 21, 2021 at 07:39:10PM +0800, Su Yue wrote:
while running xfstests on 32 bits test box, many tests failed
because of
warnings in dmesg. One of those warnings(btrfs/003):
========================================================================
[ 66.441305] ------------[ cut here ]------------
[ 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
[ 66.441846] ---[ end trace 7a9311b3f90a392e ]---
========================================================================
========================================================================
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 "volumes.c:2994" is btrfs_device_set_bytes_used() with
mutex lock
&fs_info->chunk_mutex hold already.
My bad. btrfs_get/set_device_*() -> btrfs_device_get/set_*()
After adding some debug prints, the cause was found that manyq
__alloc_device() are called with NULL @fs_info. Inside the
function,
btrfs_device_data_ordered_init() is expanded to
seqcount_mutex_init().
In this scenario, its second parameter(&info->chunk_mutex)
passed is
&NULL->chunk_mutex which equals to offsetof(struct
btrfs_fs_info,
chunk_mutex) unexpectly. Thus, seqcount_mutex_init() is called
in wrong
way. And later btrfs_get/set_device_*() helpers triger lockdep
warnings.
Same here.
The complex solution is to delay the call of
btrfs_device_data_ordered_
init() so the lockdep functionality can work well.
It requires that no btrfs_get/set_device_*() is called between
btrfs_alloc_device with NULL @fs_info and the delayed
btrfs_device_data_ordered_init(). Otherwise, total_bytes,
disk_total_
bytes and bytes_uesed of device may be inconsistent in 32 bits
environments.
If the fs_info is not available at all times, would it be
possible to
set it once it is? (And reset when the fs_info is released).
Please correct me if I am wrong. AFAIK,
btrfs_device_data_ordered_init()
can be called correctly but only for the first time.
Looking at include/linux/seqlock.h, seqcount_mutex_t::lock is
touched
only in its initial timing. So when fs_info is released, there is
not api to reset the seqcount_mutex_t::lock. Then warnings are
still
there. Or we can allocate btrfs_device::data_seqcount in runtime.
But is it worth changing struct btrfs_device only for the lockdep
reason on 32 bits machines?
