Hello,
I've been seeing a variation of the following splat recently and I have no
earthly idea what it's trying to tell me. I either get this one, or I get one
that tells me the same thing except it's complaining about &cpuctx_mutex instead
of sb_pagefaults. There is no place we take the reloc_mutex and then do the
pagefaults stuff, so I don't know where it's getting these dependencies from.
The stacktraces make no sense because there's perf stuff in here, but it doesn't
show me a path where we would be holding _any_ btrfs locks, so I'm not sure how
we gain those dependencies. Can you tell me where I'm being stupid? Thanks,
======================================================
WARNING: possible circular locking dependency detected
5.2.0-rc7-00100-ga4067edd7814 #671 Not tainted
------------------------------------------------------
python3.6/44461 is trying to acquire lock:
00000000674af011 (&fs_info->reloc_mutex){+.+.}, at: btrfs_record_root_in_trans+0x3c/0x70
but task is already holding lock:
0000000091a6f027 (sb_pagefaults){.+.+}, at: btrfs_page_mkwrite+0x6a/0x4f0
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #10 (sb_pagefaults){.+.+}:
__sb_start_write+0x12f/0x1d0
btrfs_page_mkwrite+0x6a/0x4f0
do_page_mkwrite+0x2b/0x70
__handle_mm_fault+0x6f2/0x10e0
handle_mm_fault+0x179/0x360
__do_page_fault+0x24d/0x4d0
page_fault+0x1e/0x30
-> #9 (&mm->mmap_sem#2){++++}:
__might_fault+0x6b/0x90
_copy_to_user+0x1e/0x70
perf_read+0x1a9/0x2c0
vfs_read+0x9b/0x150
ksys_read+0x5c/0xd0
do_syscall_64+0x4a/0x1b0
entry_SYSCALL_64_after_hwframe+0x49/0xbe
-> #8 (&cpuctx_mutex){+.+.}:
__mutex_lock+0x81/0x8f0
perf_event_init_cpu+0x9c/0x150
perf_event_init+0x1d0/0x1fe
start_kernel+0x365/0x513
secondary_startup_64+0xa4/0xb0
-> #7 (pmus_lock){+.+.}:
__mutex_lock+0x81/0x8f0
perf_event_init_cpu+0x69/0x150
cpuhp_invoke_callback+0xb8/0x950
_cpu_up.constprop.29+0xad/0x140
do_cpu_up+0x92/0xe0
smp_init+0xcf/0xd4
kernel_init_freeable+0x13a/0x290
kernel_init+0xa/0x110
ret_from_fork+0x24/0x30
-> #6 (cpu_hotplug_lock.rw_sem){++++}:
cpus_read_lock+0x43/0x90
kmem_cache_create_usercopy+0x28/0x250
kmem_cache_create+0x18/0x20
bioset_init+0x157/0x2a0
init_bio+0xa1/0xa7
do_one_initcall+0x67/0x2f4
kernel_init_freeable+0x1ec/0x290
kernel_init+0xa/0x110
ret_from_fork+0x24/0x30
-> #5 (bio_slab_lock){+.+.}:
__mutex_lock+0x81/0x8f0
bioset_init+0xb0/0x2a0
blk_alloc_queue_node+0x80/0x2d0
blk_mq_init_queue+0x1b/0x60
0xffffffffa0022131
do_one_initcall+0x67/0x2f4
do_init_module+0x5a/0x22e
load_module+0x1ebc/0x2570
__do_sys_finit_module+0xb2/0xc0
do_syscall_64+0x4a/0x1b0
entry_SYSCALL_64_after_hwframe+0x49/0xbe
-> #4 (loop_ctl_mutex){+.+.}:
__mutex_lock+0x81/0x8f0
__blkdev_get+0xba/0x530
blkdev_get+0x1bd/0x340
do_dentry_open+0x1fb/0x390
path_openat+0x4f7/0xd30
do_filp_open+0x91/0x100
do_sys_open+0x127/0x220
do_syscall_64+0x4a/0x1b0
entry_SYSCALL_64_after_hwframe+0x49/0xbe
-> #3 (&bdev->bd_mutex){+.+.}:
__mutex_lock+0x81/0x8f0
__blkdev_get+0x158/0x530
blkdev_get+0x21f/0x340
blkdev_get_by_path+0x4a/0x80
btrfs_get_bdev_and_sb+0x1b/0xb0
open_fs_devices+0x15d/0x290
btrfs_open_devices+0x75/0xa0
btrfs_mount_root+0x237/0x680
legacy_get_tree+0x2d/0x50
vfs_get_tree+0x1e/0x100
fc_mount+0xe/0x40
vfs_kern_mount+0x7c/0x90
btrfs_mount+0x15b/0x82d
legacy_get_tree+0x2d/0x50
vfs_get_tree+0x1e/0x100
do_mount+0x6ee/0xab0
ksys_mount+0x7e/0xd0
__x64_sys_mount+0x21/0x30
do_syscall_64+0x4a/0x1b0
entry_SYSCALL_64_after_hwframe+0x49/0xbe
-> #2 (&fs_devs->device_list_mutex){+.+.}:
__mutex_lock+0x81/0x8f0
btrfs_run_dev_stats+0x4d/0x3c0
commit_cowonly_roots+0xb2/0x2a0
btrfs_commit_transaction+0x524/0xa80
btrfs_recover_log_trees+0x366/0x470
open_ctree+0x20a1/0x22dd
btrfs_mount_root+0x51e/0x680
legacy_get_tree+0x2d/0x50
vfs_get_tree+0x1e/0x100
fc_mount+0xe/0x40
vfs_kern_mount+0x7c/0x90
btrfs_mount+0x15b/0x82d
legacy_get_tree+0x2d/0x50
vfs_get_tree+0x1e/0x100
do_mount+0x6ee/0xab0
ksys_mount+0x7e/0xd0
__x64_sys_mount+0x21/0x30
do_syscall_64+0x4a/0x1b0
entry_SYSCALL_64_after_hwframe+0x49/0xbe
-> #1 (&fs_info->tree_log_mutex){+.+.}:
__mutex_lock+0x81/0x8f0
btrfs_commit_transaction+0x4c9/0xa80
btrfs_recover_log_trees+0x366/0x470
open_ctree+0x20a1/0x22dd
btrfs_mount_root+0x51e/0x680
legacy_get_tree+0x2d/0x50
vfs_get_tree+0x1e/0x100
fc_mount+0xe/0x40
vfs_kern_mount+0x7c/0x90
btrfs_mount+0x15b/0x82d
legacy_get_tree+0x2d/0x50
vfs_get_tree+0x1e/0x100
do_mount+0x6ee/0xab0
ksys_mount+0x7e/0xd0
__x64_sys_mount+0x21/0x30
do_syscall_64+0x4a/0x1b0
entry_SYSCALL_64_after_hwframe+0x49/0xbe
-> #0 (&fs_info->reloc_mutex){+.+.}:
lock_acquire+0xb0/0x1a0
__mutex_lock+0x81/0x8f0
btrfs_record_root_in_trans+0x3c/0x70
start_transaction+0xaa/0x510
btrfs_dirty_inode+0x49/0xe0
file_update_time+0xc7/0x110
btrfs_page_mkwrite+0x152/0x4f0
do_page_mkwrite+0x2b/0x70
do_wp_page+0x4b1/0x5e0
__handle_mm_fault+0x6b8/0x10e0
handle_mm_fault+0x179/0x360
__do_page_fault+0x24d/0x4d0
page_fault+0x1e/0x30
other info that might help us debug this:
Chain exists of:
&fs_info->reloc_mutex --> &mm->mmap_sem#2 --> sb_pagefaults
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(sb_pagefaults);
lock(&mm->mmap_sem#2);
lock(sb_pagefaults);
lock(&fs_info->reloc_mutex);
*** DEADLOCK ***
3 locks held by python3.6/44461:
#0: 000000005a6ec7ac (&mm->mmap_sem#2){++++}, at: __do_page_fault+0x13d/0x4d0
#1: 0000000091a6f027 (sb_pagefaults){.+.+}, at: btrfs_page_mkwrite+0x6a/0x4f0
#2: 00000000a7f74f74 (sb_internal){.+.+}, at: start_transaction+0x36b/0x510
stack backtrace:
CPU: 10 PID: 44461 Comm: python3.6 Kdump: loaded Not tainted 5.2.0-rc7-00100-ga4067edd7814 #671
Hardware name: Quanta Leopard ORv2-DDR4/Leopard ORv2-DDR4, BIOS F06_3B17 03/16/2018
Call Trace:
dump_stack+0x5e/0x8b
print_circular_bug+0x1f1/0x1fe
__lock_acquire+0x1724/0x1970
? find_held_lock+0x31/0xa0
lock_acquire+0xb0/0x1a0
? btrfs_record_root_in_trans+0x3c/0x70
? btrfs_record_root_in_trans+0x3c/0x70
__mutex_lock+0x81/0x8f0
? btrfs_record_root_in_trans+0x3c/0x70
? find_held_lock+0x31/0xa0
? btrfs_record_root_in_trans+0x3c/0x70
? join_transaction+0x39f/0x3f0
btrfs_record_root_in_trans+0x3c/0x70
start_transaction+0xaa/0x510
btrfs_dirty_inode+0x49/0xe0
? current_time+0x46/0x80
file_update_time+0xc7/0x110
btrfs_page_mkwrite+0x152/0x4f0
? find_held_lock+0x31/0xa0
? do_wp_page+0x4a9/0x5e0
do_page_mkwrite+0x2b/0x70
do_wp_page+0x4b1/0x5e0
__handle_mm_fault+0x6b8/0x10e0
handle_mm_fault+0x179/0x360
? handle_mm_fault+0x46/0x360
__do_page_fault+0x24d/0x4d0
? page_fault+0x8/0x30
page_fault+0x1e/0x30
RIP: 0033:0x7fe888361860
Code: 00 48 89 df e8 e1 2b ff ff 48 89 c3 48 83 f8 ff 74 2b 4c 89 e1 45 0f b7 45 00 0f b7 c0 48 c1 f9 10 75 4b 48 8b 05 18 d7 20 00 <66> 41 89 5d 00 48 ff 00 48 83 c4 08 5b 41 5c 41 5d 5d c3 e8 a8 2c
RSP: 002b:00007fff4ab2ea70 EFLAGS: 00010246
RAX: 00007fe8b101c110 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 00007fe8b1538708 RSI: 00007fe8b1014040 RDI: 00007fe8b1066d00
RBP: 00007fff4ab2ea90 R08: 0000000000000000 R09: 0000000000000000
R10: 00007fe8885843e0 R11: 00007fe8b1026540 R12: 0000000000000002
R13: 00007fe8b138e000 R14: 00007fe886ace730 R15: 00007fe8b1066d00
