From 6134a4bb6b1c411a244edee041ac89266c78d45c Mon Sep 17 00:00:00 2001
From: Filipe Manana
Date: Wed, 22 Mar 2023 09:46:34 +0000
Subject: btrfs: fix deadlock when aborting transaction during relocation with
scrub
commit 2d82a40aa7d6fcae0250ec68b8566cdee7bfd44c upstream.
Before relocating a block group we pause scrub, then do the relocation and
then unpause scrub. The relocation process requires starting and committing
a transaction, and if we have a failure in the critical section of the
transaction commit path (transaction state >= TRANS_STATE_COMMIT_START),
we will deadlock if there is a paused scrub.
That results in stack traces like the following:
[42.479] BTRFS info (device sdc): relocating block group 53876686848 flags metadata|raid6
[42.936] BTRFS warning (device sdc): Skipping commit of aborted transaction.
[42.936] ------------[ cut here ]------------
[42.936] BTRFS: Transaction aborted (error -28)
[42.936] WARNING: CPU: 11 PID: 346822 at fs/btrfs/transaction.c:1977 btrfs_commit_transaction+0xcc8/0xeb0 [btrfs]
[42.936] Modules linked in: dm_flakey dm_mod loop btrfs (...)
[42.936] CPU: 11 PID: 346822 Comm: btrfs Tainted: G W 6.3.0-rc2-btrfs-next-127+ #1
[42.936] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014
[42.936] RIP: 0010:btrfs_commit_transaction+0xcc8/0xeb0 [btrfs]
[42.936] Code: ff ff 45 8b (...)
[42.936] RSP: 0018:ffffb58649633b48 EFLAGS: 00010282
[42.936] RAX: 0000000000000000 RBX: ffff8be6ef4d5bd8 RCX: 0000000000000000
[42.936] RDX: 0000000000000002 RSI: ffffffffb35e7782 RDI: 00000000ffffffff
[42.936] RBP: ffff8be6ef4d5c98 R08: 0000000000000000 R09: ffffb586496339e8
[42.936] R10: 0000000000000001 R11: 0000000000000001 R12: ffff8be6d38c7c00
[42.936] R13: 00000000ffffffe4 R14: ffff8be6c268c000 R15: ffff8be6ef4d5cf0
[42.936] FS: 00007f381a82b340(0000) GS:ffff8beddfcc0000(0000) knlGS:0000000000000000
[42.936] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[42.936] CR2: 00007f1e35fb7638 CR3: 0000000117680006 CR4: 0000000000370ee0
[42.936] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[42.936] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[42.936] Call Trace:
[42.936]
[42.936] ? start_transaction+0xcb/0x610 [btrfs]
[42.936] prepare_to_relocate+0x111/0x1a0 [btrfs]
[42.936] relocate_block_group+0x57/0x5d0 [btrfs]
[42.936] ? btrfs_wait_nocow_writers+0x25/0xb0 [btrfs]
[42.936] btrfs_relocate_block_group+0x248/0x3c0 [btrfs]
[42.936] ? __pfx_autoremove_wake_function+0x10/0x10
[42.936] btrfs_relocate_chunk+0x3b/0x150 [btrfs]
[42.936] btrfs_balance+0x8ff/0x11d0 [btrfs]
[42.936] ? __kmem_cache_alloc_node+0x14a/0x410
[42.936] btrfs_ioctl+0x2334/0x32c0 [btrfs]
[42.937] ? mod_objcg_state+0xd2/0x360
[42.937] ? refill_obj_stock+0xb0/0x160
[42.937] ? seq_release+0x25/0x30
[42.937] ? __rseq_handle_notify_resume+0x3b5/0x4b0
[42.937] ? percpu_counter_add_batch+0x2e/0xa0
[42.937] ? __x64_sys_ioctl+0x88/0xc0
[42.937] __x64_sys_ioctl+0x88/0xc0
[42.937] do_syscall_64+0x38/0x90
[42.937] entry_SYSCALL_64_after_hwframe+0x72/0xdc
[42.937] RIP: 0033:0x7f381a6ffe9b
[42.937] Code: 00 48 89 44 24 (...)
[42.937] RSP: 002b:00007ffd45ecf060 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
[42.937] RAX: ffffffffffffffda RBX: 0000000000000001 RCX: 00007f381a6ffe9b
[42.937] RDX: 00007ffd45ecf150 RSI: 00000000c4009420 RDI: 0000000000000003
[42.937] RBP: 0000000000000003 R08: 0000000000000013 R09: 0000000000000000
[42.937] R10: 00007f381a60c878 R11: 0000000000000246 R12: 00007ffd45ed0423
[42.937] R13: 00007ffd45ecf150 R14: 0000000000000000 R15: 00007ffd45ecf148
[42.937]
[42.937] ---[ end trace 0000000000000000 ]---
[42.937] BTRFS: error (device sdc: state A) in cleanup_transaction:1977: errno=-28 No space left
[59.196] INFO: task btrfs:346772 blocked for more than 120 seconds.
[59.196] Tainted: G W 6.3.0-rc2-btrfs-next-127+ #1
[59.196] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[59.196] task:btrfs state:D stack:0 pid:346772 ppid:1 flags:0x00004002
[59.196] Call Trace:
[59.196]
[59.196] __schedule+0x392/0xa70
[59.196] ? __pv_queued_spin_lock_slowpath+0x165/0x370
[59.196] schedule+0x5d/0xd0
[59.196] __scrub_blocked_if_needed+0x74/0xc0 [btrfs]
[59.197] ? __pfx_autoremove_wake_function+0x10/0x10
[59.197] scrub_pause_off+0x21/0x50 [btrfs]
[59.197] scrub_simple_mirror+0x1c7/0x950 [btrfs]
[59.197] ? scrub_parity_put+0x1a5/0x1d0 [btrfs]
[59.198] ? __pfx_autoremove_wake_function+0x10/0x10
[59.198] scrub_stripe+0x20d/0x740 [btrfs]
[59.198] scrub_chunk+0xc4/0x130 [btrfs]
[59.198] scrub_enumerate_chunks+0x3e4/0x7a0 [btrfs]
[59.198] ? __pfx_autoremove_wake_function+0x10/0x10
[59.198] btrfs_scrub_dev+0x236/0x6a0 [btrfs]
[59.199] ? btrfs_ioctl+0xd97/0x32c0 [btrfs]
[59.199] ? _copy_from_user+0x7b/0x80
[59.199] btrfs_ioctl+0xde1/0x32c0 [btrfs]
[59.199] ? refill_stock+0x33/0x50
[59.199] ? should_failslab+0xa/0x20
[59.199] ? kmem_cache_alloc_node+0x151/0x460
[59.199] ? alloc_io_context+0x1b/0x80
[59.199] ? preempt_count_add+0x70/0xa0
[59.199] ? __x64_sys_ioctl+0x88/0xc0
[59.199] __x64_sys_ioctl+0x88/0xc0
[59.199] do_syscall_64+0x38/0x90
[59.199] entry_SYSCALL_64_after_hwframe+0x72/0xdc
[59.199] RIP: 0033:0x7f82ffaffe9b
[59.199] RSP: 002b:00007f82ff9fcc50 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
[59.199] RAX: ffffffffffffffda RBX: 000055b191e36310 RCX: 00007f82ffaffe9b
[59.199] RDX: 000055b191e36310 RSI: 00000000c400941b RDI: 0000000000000003
[59.199] RBP: 0000000000000000 R08: 00007fff1575016f R09: 0000000000000000
[59.199] R10: 0000000000000000 R11: 0000000000000246 R12: 00007f82ff9fd640
[59.199] R13: 000000000000006b R14: 00007f82ffa87580 R15: 0000000000000000
[59.199]
[59.199] INFO: task btrfs:346773 blocked for more than 120 seconds.
[59.200] Tainted: G W 6.3.0-rc2-btrfs-next-127+ #1
[59.200] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[59.201] task:btrfs state:D stack:0 pid:346773 ppid:1 flags:0x00004002
[59.201] Call Trace:
[59.201]
[59.201] __schedule+0x392/0xa70
[59.201] ? __pv_queued_spin_lock_slowpath+0x165/0x370
[59.201] schedule+0x5d/0xd0
[59.201] __scrub_blocked_if_needed+0x74/0xc0 [btrfs]
[59.201] ? __pfx_autoremove_wake_function+0x10/0x10
[59.201] scrub_pause_off+0x21/0x50 [btrfs]
[59.202] scrub_simple_mirror+0x1c7/0x950 [btrfs]
[59.202] ? scrub_parity_put+0x1a5/0x1d0 [btrfs]
[59.202] ? __pfx_autoremove_wake_function+0x10/0x10
[59.202] scrub_stripe+0x20d/0x740 [btrfs]
[59.202] scrub_chunk+0xc4/0x130 [btrfs]
[59.203] scrub_enumerate_chunks+0x3e4/0x7a0 [btrfs]
[59.203] ? __pfx_autoremove_wake_function+0x10/0x10
[59.203] btrfs_scrub_dev+0x236/0x6a0 [btrfs]
[59.203] ? btrfs_ioctl+0xd97/0x32c0 [btrfs]
[59.203] ? _copy_from_user+0x7b/0x80
[59.203] btrfs_ioctl+0xde1/0x32c0 [btrfs]
[59.204] ? should_failslab+0xa/0x20
[59.204] ? kmem_cache_alloc_node+0x151/0x460
[59.204] ? alloc_io_context+0x1b/0x80
[59.204] ? preempt_count_add+0x70/0xa0
[59.204] ? __x64_sys_ioctl+0x88/0xc0
[59.204] __x64_sys_ioctl+0x88/0xc0
[59.204] do_syscall_64+0x38/0x90
[59.204] entry_SYSCALL_64_after_hwframe+0x72/0xdc
[59.204] RIP: 0033:0x7f82ffaffe9b
[59.204] RSP: 002b:00007f82ff1fbc50 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
[59.204] RAX: ffffffffffffffda RBX: 000055b191e36790 RCX: 00007f82ffaffe9b
[59.204] RDX: 000055b191e36790 RSI: 00000000c400941b RDI: 0000000000000003
[59.204] RBP: 0000000000000000 R08: 00007fff1575016f R09: 0000000000000000
[59.204] R10: 0000000000000000 R11: 0000000000000246 R12: 00007f82ff1fc640
[59.204] R13: 000000000000006b R14: 00007f82ffa87580 R15: 0000000000000000
[59.204]
[59.204] INFO: task btrfs:346774 blocked for more than 120 seconds.
[59.205] Tainted: G W 6.3.0-rc2-btrfs-next-127+ #1
[59.205] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[59.206] task:btrfs state:D stack:0 pid:346774 ppid:1 flags:0x00004002
[59.206] Call Trace:
[59.206]
[59.206] __schedule+0x392/0xa70
[59.206] schedule+0x5d/0xd0
[59.206] __scrub_blocked_if_needed+0x74/0xc0 [btrfs]
[59.206] ? __pfx_autoremove_wake_function+0x10/0x10
[59.206] scrub_pause_off+0x21/0x50 [btrfs]
[59.207] scrub_simple_mirror+0x1c7/0x950 [btrfs]
[59.207] ? scrub_parity_put+0x1a5/0x1d0 [btrfs]
[59.207] ? __pfx_autoremove_wake_function+0x10/0x10
[59.207] scrub_stripe+0x20d/0x740 [btrfs]
[59.208] scrub_chunk+0xc4/0x130 [btrfs]
[59.208] scrub_enumerate_chunks+0x3e4/0x7a0 [btrfs]
[59.208] ? __mutex_unlock_slowpath.isra.0+0x9a/0x120
[59.208] btrfs_scrub_dev+0x236/0x6a0 [btrfs]
[59.208] ? btrfs_ioctl+0xd97/0x32c0 [btrfs]
[59.209] ? _copy_from_user+0x7b/0x80
[59.209] btrfs_ioctl+0xde1/0x32c0 [btrfs]
[59.209] ? should_failslab+0xa/0x20
[59.209] ? kmem_cache_alloc_node+0x151/0x460
[59.209] ? alloc_io_context+0x1b/0x80
[59.209] ? preempt_count_add+0x70/0xa0
[59.209] ? __x64_sys_ioctl+0x88/0xc0
[59.209] __x64_sys_ioctl+0x88/0xc0
[59.209] do_syscall_64+0x38/0x90
[59.209] entry_SYSCALL_64_after_hwframe+0x72/0xdc
[59.209] RIP: 0033:0x7f82ffaffe9b
[59.209] RSP: 002b:00007f82fe9fac50 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
[59.209] RAX: ffffffffffffffda RBX: 000055b191e36c10 RCX: 00007f82ffaffe9b
[59.209] RDX: 000055b191e36c10 RSI: 00000000c400941b RDI: 0000000000000003
[59.209] RBP: 0000000000000000 R08: 00007fff1575016f R09: 0000000000000000
[59.209] R10: 0000000000000000 R11: 0000000000000246 R12: 00007f82fe9fb640
[59.209] R13: 000000000000006b R14: 00007f82ffa87580 R15: 0000000000000000
[59.209]
[59.209] INFO: task btrfs:346775 blocked for more than 120 seconds.
[59.210] Tainted: G W 6.3.0-rc2-btrfs-next-127+ #1
[59.210] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[59.211] task:btrfs state:D stack:0 pid:346775 ppid:1 flags:0x00004002
[59.211] Call Trace:
[59.211]
[59.211] __schedule+0x392/0xa70
[59.211] schedule+0x5d/0xd0
[59.211] __scrub_blocked_if_needed+0x74/0xc0 [btrfs]
[59.211] ? __pfx_autoremove_wake_function+0x10/0x10
[59.211] scrub_pause_off+0x21/0x50 [btrfs]
[59.212] scrub_simple_mirror+0x1c7/0x950 [btrfs]
[59.212] ? scrub_parity_put+0x1a5/0x1d0 [btrfs]
[59.212] ? __pfx_autoremove_wake_function+0x10/0x10
[59.212] scrub_stripe+0x20d/0x740 [btrfs]
[59.213] scrub_chunk+0xc4/0x130 [btrfs]
[59.213] scrub_enumerate_chunks+0x3e4/0x7a0 [btrfs]
[59.213] ? __mutex_unlock_slowpath.isra.0+0x9a/0x120
[59.213] btrfs_scrub_dev+0x236/0x6a0 [btrfs]
[59.213] ? btrfs_ioctl+0xd97/0x32c0 [btrfs]
[59.214] ? _copy_from_user+0x7b/0x80
[59.214] btrfs_ioctl+0xde1/0x32c0 [btrfs]
[59.214] ? should_failslab+0xa/0x20
[59.214] ? kmem_cache_alloc_node+0x151/0x460
[59.214] ? alloc_io_context+0x1b/0x80
[59.214] ? preempt_count_add+0x70/0xa0
[59.214] ? __x64_sys_ioctl+0x88/0xc0
[59.214] __x64_sys_ioctl+0x88/0xc0
[59.214] do_syscall_64+0x38/0x90
[59.214] entry_SYSCALL_64_after_hwframe+0x72/0xdc
[59.214] RIP: 0033:0x7f82ffaffe9b
[59.214] RSP: 002b:00007f82fe1f9c50 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
[59.214] RAX: ffffffffffffffda RBX: 000055b191e37090 RCX: 00007f82ffaffe9b
[59.214] RDX: 000055b191e37090 RSI: 00000000c400941b RDI: 0000000000000003
[59.214] RBP: 0000000000000000 R08: 00007fff1575016f R09: 0000000000000000
[59.214] R10: 0000000000000000 R11: 0000000000000246 R12: 00007f82fe1fa640
[59.214] R13: 000000000000006b R14: 00007f82ffa87580 R15: 0000000000000000
[59.214]
[59.214] INFO: task btrfs:346776 blocked for more than 120 seconds.
[59.215] Tainted: G W 6.3.0-rc2-btrfs-next-127+ #1
[59.216] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[59.217] task:btrfs state:D stack:0 pid:346776 ppid:1 flags:0x00004002
[59.217] Call Trace:
[59.217]
[59.217] __schedule+0x392/0xa70
[59.217] ? __pv_queued_spin_lock_slowpath+0x165/0x370
[59.217] schedule+0x5d/0xd0
[59.217] __scrub_blocked_if_needed+0x74/0xc0 [btrfs]
[59.217] ? __pfx_autoremove_wake_function+0x10/0x10
[59.217] scrub_pause_off+0x21/0x50 [btrfs]
[59.217] scrub_simple_mirror+0x1c7/0x950 [btrfs]
[59.217] ? scrub_parity_put+0x1a5/0x1d0 [btrfs]
[59.218] ? __pfx_autoremove_wake_function+0x10/0x10
[59.218] scrub_stripe+0x20d/0x740 [btrfs]
[59.218] scrub_chunk+0xc4/0x130 [btrfs]
[59.218] scrub_enumerate_chunks+0x3e4/0x7a0 [btrfs]
[59.219] ? __pfx_autoremove_wake_function+0x10/0x10
[59.219] btrfs_scrub_dev+0x236/0x6a0 [btrfs]
[59.219] ? btrfs_ioctl+0xd97/0x32c0 [btrfs]
[59.219] ? _copy_from_user+0x7b/0x80
[59.219] btrfs_ioctl+0xde1/0x32c0 [btrfs]
[59.219] ? should_failslab+0xa/0x20
[59.219] ? kmem_cache_alloc_node+0x151/0x460
[59.219] ? alloc_io_context+0x1b/0x80
[59.219] ? preempt_count_add+0x70/0xa0
[59.219] ? __x64_sys_ioctl+0x88/0xc0
[59.219] __x64_sys_ioctl+0x88/0xc0
[59.219] do_syscall_64+0x38/0x90
[59.219] entry_SYSCALL_64_after_hwframe+0x72/0xdc
[59.219] RIP: 0033:0x7f82ffaffe9b
[59.219] RSP: 002b:00007f82fd9f8c50 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
[59.219] RAX: ffffffffffffffda RBX: 000055b191e37510 RCX: 00007f82ffaffe9b
[59.219] RDX: 000055b191e37510 RSI: 00000000c400941b RDI: 0000000000000003
[59.219] RBP: 0000000000000000 R08: 00007fff1575016f R09: 0000000000000000
[59.219] R10: 0000000000000000 R11: 0000000000000246 R12: 00007f82fd9f9640
[59.219] R13: 000000000000006b R14: 00007f82ffa87580 R15: 0000000000000000
[59.219]
[59.219] INFO: task btrfs:346822 blocked for more than 120 seconds.
[59.220] Tainted: G W 6.3.0-rc2-btrfs-next-127+ #1
[59.221] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[59.222] task:btrfs state:D stack:0 pid:346822 ppid:1 flags:0x00004002
[59.222] Call Trace:
[59.222]
[59.222] __schedule+0x392/0xa70
[59.222] schedule+0x5d/0xd0
[59.222] btrfs_scrub_cancel+0x91/0x100 [btrfs]
[59.222] ? __pfx_autoremove_wake_function+0x10/0x10
[59.222] btrfs_commit_transaction+0x572/0xeb0 [btrfs]
[59.223] ? start_transaction+0xcb/0x610 [btrfs]
[59.223] prepare_to_relocate+0x111/0x1a0 [btrfs]
[59.223] relocate_block_group+0x57/0x5d0 [btrfs]
[59.223] ? btrfs_wait_nocow_writers+0x25/0xb0 [btrfs]
[59.223] btrfs_relocate_block_group+0x248/0x3c0 [btrfs]
[59.224] ? __pfx_autoremove_wake_function+0x10/0x10
[59.224] btrfs_relocate_chunk+0x3b/0x150 [btrfs]
[59.224] btrfs_balance+0x8ff/0x11d0 [btrfs]
[59.224] ? __kmem_cache_alloc_node+0x14a/0x410
[59.224] btrfs_ioctl+0x2334/0x32c0 [btrfs]
[59.225] ? mod_objcg_state+0xd2/0x360
[59.225] ? refill_obj_stock+0xb0/0x160
[59.225] ? seq_release+0x25/0x30
[59.225] ? __rseq_handle_notify_resume+0x3b5/0x4b0
[59.225] ? percpu_counter_add_batch+0x2e/0xa0
[59.225] ? __x64_sys_ioctl+0x88/0xc0
[59.225] __x64_sys_ioctl+0x88/0xc0
[59.225] do_syscall_64+0x38/0x90
[59.225] entry_SYSCALL_64_after_hwframe+0x72/0xdc
[59.225] RIP: 0033:0x7f381a6ffe9b
[59.225] RSP: 002b:00007ffd45ecf060 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
[59.225] RAX: ffffffffffffffda RBX: 0000000000000001 RCX: 00007f381a6ffe9b
[59.225] RDX: 00007ffd45ecf150 RSI: 00000000c4009420 RDI: 0000000000000003
[59.225] RBP: 0000000000000003 R08: 0000000000000013 R09: 0000000000000000
[59.225] R10: 00007f381a60c878 R11: 0000000000000246 R12: 00007ffd45ed0423
[59.225] R13: 00007ffd45ecf150 R14: 0000000000000000 R15: 00007ffd45ecf148
[59.225]
What happens is the following:
1) A scrub is running, so fs_info->scrubs_running is 1;
2) Task A starts block group relocation, and at btrfs_relocate_chunk() it
pauses scrub by calling btrfs_scrub_pause(). That increments
fs_info->scrub_pause_req from 0 to 1 and waits for the scrub task to
pause (for fs_info->scrubs_paused to be == to fs_info->scrubs_running);
3) The scrub task pauses at scrub_pause_off(), waiting for
fs_info->scrub_pause_req to decrease to 0;
4) Task A then enters btrfs_relocate_block_group(), and down that call
chain we start a transaction and then attempt to commit it;
5) When task A calls btrfs_commit_transaction(), it either will do the
commit itself or wait for some other task that already started the
commit of the transaction - it doesn't matter which case;
6) The transaction commit enters state TRANS_STATE_COMMIT_START;
7) An error happens during the transaction commit, like -ENOSPC when
running delayed refs or delayed items for example;
8) This results in calling transaction.c:cleanup_transaction(), where
we call btrfs_scrub_cancel(), incrementing fs_info->scrub_cancel_req
from 0 to 1, and blocking this task waiting for fs_info->scrubs_running
to decrease to 0;
9) From this point on, both the transaction commit and the scrub task
hang forever:
1) The transaction commit is waiting for fs_info->scrubs_running to
be decreased to 0;
2) The scrub task is at scrub_pause_off() waiting for
fs_info->scrub_pause_req to decrease to 0 - so it can not proceed
to stop the scrub and decrement fs_info->scrubs_running from 0 to 1.
Therefore resulting in a deadlock.
Fix this by having cleanup_transaction(), called if a transaction commit
fails, not call btrfs_scrub_cancel() if relocation is in progress, and
having btrfs_relocate_block_group() call btrfs_scrub_cancel() instead if
the relocation failed and a transaction abort happened.
This was triggered with btrfs/061 from fstests.
Fixes: 55e3a601c81c ("btrfs: Fix data checksum error cause by replace with io-load.")
CC: stable@vger.kernel.org # 4.14+
Reviewed-by: Josef Bacik
Signed-off-by: Filipe Manana
Signed-off-by: David Sterba
Signed-off-by: Greg Kroah-Hartman
---
fs/btrfs/transaction.c | 15 ++++++++++++++-
1 file changed, 14 insertions(+), 1 deletion(-)
(limited to 'fs/btrfs/transaction.c')
diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index d1f1da6820fb..682b463a7633 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -2009,7 +2009,20 @@ static void cleanup_transaction(struct btrfs_trans_handle *trans, int err)
if (current->journal_info == trans)
current->journal_info = NULL;
- btrfs_scrub_cancel(fs_info);
+
+ /*
+ * If relocation is running, we can't cancel scrub because that will
+ * result in a deadlock. Before relocating a block group, relocation
+ * pauses scrub, then starts and commits a transaction before unpausing
+ * scrub. If the transaction commit is being done by the relocation
+ * task or triggered by another task and the relocation task is waiting
+ * for the commit, and we end up here due to an error in the commit
+ * path, then calling btrfs_scrub_cancel() will deadlock, as we are
+ * asking for scrub to stop while having it asked to be paused higher
+ * above in relocation code.
+ */
+ if (!test_bit(BTRFS_FS_RELOC_RUNNING, &fs_info->flags))
+ btrfs_scrub_cancel(fs_info);
kmem_cache_free(btrfs_trans_handle_cachep, trans);
}
--
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