Re: [LKP] Re: 28307d938f ("percpu: make pcpu_alloc() aware of current gfp .."): BUG: kernel reboot-without-warning in boot stage
On 6/2/20 8:18 PM, Filipe Manana wrote: On 02/06/20 05:37, Li Zhijian wrote: Hi Filipe, LKP checked blow dmesg as the indicator in this problem [ 0.144174] RAMDISK: [mem 0x7fa2e000-0x7fff] [ 0.144559] ACPI: Early table checksum verification disabled [ 0.144985] ACPI: RSDP 0x000F5850 14 (v00 BOCHS ) [ 0.145424] ACPI: RSDT 0xBFFE15C9 30 (v01 BOCHS BXPCRSDT 0001 BXPC 0001) [ 0.146051] ACPI: FACP 0xBFFE149D 74 (v01 BOCHS BXPCFACP 0001 BXPC 0001) BUG: kernel reboot-without-warning in boot stage And i have reproduced it with script in attachment. this issue is gone when i reverted this commit 28307d938f Please note that - i reproduced it with kernel compiled by gcc-5 - i failed to reproduce it in kernel compiled by gcc-7 so far Odd. Indeed ! i tested gcc-5 gcc-6 gcc-7, only gcc-5 triggered this issue, kernel built with gcc6 and gcc-7 works well lizhijian@shao2-debian:~$ gcc-6 --version gcc-6 (Debian 6.5.0-2) 6.5.0 20181026 Copyright (C) 2017 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. lizhijian@shao2-debian:~$ gcc-5 --version gcc-5 (Debian 5.5.0-12) 5.5.0 20171010 Copyright (C) 2015 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. lizhijian@shao2-debian:~$ gcc-7 --version gcc-7 (Debian 7.5.0-3) 7.5.0 Copyright (C) 2017 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. Thanks Zhijian Here I tested with: $ gcc --version gcc (Debian 6.3.0-18+deb9u1) 6.3.0 20170516 Copyright (C) 2016 Free Software Foundation, Inc.
Re: [LKP] Re: 28307d938f ("percpu: make pcpu_alloc() aware of current gfp .."): BUG: kernel reboot-without-warning in boot stage
On 02/06/20 05:37, Li Zhijian wrote: > Hi Filipe, > > LKP checked blow dmesg as the indicator in this problem > >>> [ 0.144174] RAMDISK: [mem 0x7fa2e000-0x7fff] >>> [ 0.144559] ACPI: Early table checksum verification disabled >>> [ 0.144985] ACPI: RSDP 0x000F5850 14 (v00 BOCHS ) >>> [ 0.145424] ACPI: RSDT 0xBFFE15C9 30 (v01 BOCHS >>> BXPCRSDT 0001 BXPC 0001) >>> [ 0.146051] ACPI: FACP 0xBFFE149D 74 (v01 BOCHS >>> BXPCFACP 0001 BXPC 0001) >>> BUG: kernel reboot-without-warning in boot stage >>> > > And i have reproduced it with script in attachment. this issue is gone > when i reverted this commit 28307d938f > > Please note that > - i reproduced it with kernel compiled by gcc-5 > - i failed to reproduce it in kernel compiled by gcc-7 so far Odd. Here I tested with: $ gcc --version gcc (Debian 6.3.0-18+deb9u1) 6.3.0 20170516 Copyright (C) 2016 Free Software Foundation, Inc. > > :~/1787$ ./reproduce.sh obj/arch/x86/boot/bzImage > qemu-system-x86_64 -enable-kvm -cpu Haswell,+smep,+smap -kernel > obj/arch/x86/boot/bzImage -m 8192 -smp 2 -device e1000,netdev=net0 > -netdev user,id=net0,hostfwd=tcp::32032-:22 -boot order=nc -no-reboot > -watchdog i6300esb -watchdog-action debug -rtc base=localtime -serial > stdio -display none -monitor null -append root=/dev/ram0 > hung_task_panic=1 debug apic=debug sysrq_always_enabled > rcupdate.rcu_cpu_stall_timeout=100 net.ifnames=0 printk.devkmsg=on > panic=-1 softlockup_panic=1 nmi_watchdog=panic oops=panic load_ramdisk=2 > prompt_ramdisk=0 drbd.minor_count=8 systemd.log_level=err > ignore_loglevel console=tty0 earlyprintk=ttyS0,115200 > console=ttyS0,115200 vga=normal rw rcuperf.shutdown=0 watchdog_thresh=60 > early console in setup code > Wrong EFI loader signature. > early console in extract_kernel > input_data: 0x06f752d8 > input_len: 0x0130dd3c > output: 0x0100 > output_len: 0x07200a48 > kernel_total_size: 0x06826000 > needed_size: 0x0740 > trampoline_32bit: 0x0009d000 > > Decompressing Linux... Parsing ELF... done. > Booting the kernel. > [ 0.00] Linux version 5.7.0-rc4-00168-g28307d938fb2 > (lizhijian@shao2-debian) (gcc version 5.5.0 20171010 (Debian 5.5.0-12), > GNU ld (GNU Binutils for Debian) 2.34) #2 SMP PREEMPT Tue Jun 2 11:23:59 > CST 2020 > [ 0.00] Command line: root=/dev/ram0 hung_task_panic=1 debug > apic=debug sysrq_always_enabled rcupdate.rcu_cpu_stall_timeout=100 > net.ifnames=0 printk.devkmsg=on panic=-1 softlockup_panic=1 > nmi_watchdog=panic oops=panic load_ramdisk=2 prompt_ramdisk=0 > drbd.minor_count=8 systemd.log_level=err ignore_loglevel console=tty0 > earlyprintk=ttyS0,115200 console=ttyS0,115200 vga=normal rw > rcuperf.shutdown=0 watchdog_thresh=60 > [ 0.00] x86/fpu: Supporting XSAVE feature 0x001: 'x87 floating > point registers' > [ 0.00] x86/fpu: Supporting XSAVE feature 0x002: 'SSE registers' > [ 0.00] x86/fpu: Supporting XSAVE feature 0x004: 'AVX registers' > [ 0.00] x86/fpu: xstate_offset[2]: 576, xstate_sizes[2]: 256 > [ 0.00] x86/fpu: Enabled xstate features 0x7, context size is 832 > bytes, using 'standard' format. > [ 0.00] BIOS-provided physical RAM map: > [ 0.00] BIOS-e820: [mem 0x-0x0009fbff] > usable > [ 0.00] BIOS-e820: [mem 0x0009fc00-0x0009] > reserved > [ 0.00] BIOS-e820: [mem 0x000f-0x000f] > reserved > [ 0.00] BIOS-e820: [mem 0x0010-0xbffd] > usable > [ 0.00] BIOS-e820: [mem 0xbffe-0xbfff] > reserved > [ 0.00] BIOS-e820: [mem 0xfeffc000-0xfeff] > reserved > [ 0.00] BIOS-e820: [mem 0xfffc-0x] > reserved > [ 0.00] BIOS-e820: [mem 0x0001-0x00023fff] > usable > [ 0.00] printk: debug: ignoring loglevel setting. > [ 0.00] printk: bootconsole [earlyser0] enabled > [ 0.00] NX (Execute Disable) protection: active > [ 0.00] SMBIOS 2.8 present. > [ 0.00] DMI: QEMU Standard PC (i440FX + PIIX, 1996), BIOS > 1.12.0-1 04/01/2014 > [ 0.00] Hypervisor detected: KVM > [ 0.00] kvm-clock: Using msrs 4b564d01 and 4b564d00 > [ 0.02] kvm-clock: cpu 0, msr 7601001, primary cpu clock > [ 0.02] kvm-clock: using sched offset of 2661499940 cycles > [ 0.000603] clocksource: kvm-clock: mask: 0x > max_cycles: 0x1cd42e4dffb, max_idle_ns: 881590591483 ns > [ 0.002261] tsc: Detected 3407.998 MHz processor > [ 0.005351] e820: update [mem 0x-0x0fff] usable ==> reserved > [ 0.005986] e820: remove [mem 0x000a-0x000f] usable > [ 0.006535] last_pfn = 0x24 max_arch_pfn = 0x4 > [ 0.007091] MTRR default type: write-back > [ 0.007477] MTRR fixed ranges enabled: > [ 0.007845] 0-9 write-back
Re: [LKP] Re: 28307d938f ("percpu: make pcpu_alloc() aware of current gfp .."): BUG: kernel reboot-without-warning in boot stage
Hi Filipe, LKP checked blow dmesg as the indicator in this problem [0.144174] RAMDISK: [mem 0x7fa2e000-0x7fff] [0.144559] ACPI: Early table checksum verification disabled [0.144985] ACPI: RSDP 0x000F5850 14 (v00 BOCHS ) [0.145424] ACPI: RSDT 0xBFFE15C9 30 (v01 BOCHS BXPCRSDT 0001 BXPC 0001) [0.146051] ACPI: FACP 0xBFFE149D 74 (v01 BOCHS BXPCFACP 0001 BXPC 0001) BUG: kernel reboot-without-warning in boot stage And i have reproduced it with script in attachment. this issue is gone when i reverted this commit 28307d938f Please note that - i reproduced it with kernel compiled by gcc-5 - i failed to reproduce it in kernel compiled by gcc-7 so far :~/1787$ ./reproduce.sh obj/arch/x86/boot/bzImage qemu-system-x86_64 -enable-kvm -cpu Haswell,+smep,+smap -kernel obj/arch/x86/boot/bzImage -m 8192 -smp 2 -device e1000,netdev=net0 -netdev user,id=net0,hostfwd=tcp::32032-:22 -boot order=nc -no-reboot -watchdog i6300esb -watchdog-action debug -rtc base=localtime -serial stdio -display none -monitor null -append root=/dev/ram0 hung_task_panic=1 debug apic=debug sysrq_always_enabled rcupdate.rcu_cpu_stall_timeout=100 net.ifnames=0 printk.devkmsg=on panic=-1 softlockup_panic=1 nmi_watchdog=panic oops=panic load_ramdisk=2 prompt_ramdisk=0 drbd.minor_count=8 systemd.log_level=err ignore_loglevel console=tty0 earlyprintk=ttyS0,115200 console=ttyS0,115200 vga=normal rw rcuperf.shutdown=0 watchdog_thresh=60 early console in setup code Wrong EFI loader signature. early console in extract_kernel input_data: 0x06f752d8 input_len: 0x0130dd3c output: 0x0100 output_len: 0x07200a48 kernel_total_size: 0x06826000 needed_size: 0x0740 trampoline_32bit: 0x0009d000 Decompressing Linux... Parsing ELF... done. Booting the kernel. [ 0.00] Linux version 5.7.0-rc4-00168-g28307d938fb2 (lizhijian@shao2-debian) (gcc version 5.5.0 20171010 (Debian 5.5.0-12), GNU ld (GNU Binutils for Debian) 2.34) #2 SMP PREEMPT Tue Jun 2 11:23:59 CST 2020 [ 0.00] Command line: root=/dev/ram0 hung_task_panic=1 debug apic=debug sysrq_always_enabled rcupdate.rcu_cpu_stall_timeout=100 net.ifnames=0 printk.devkmsg=on panic=-1 softlockup_panic=1 nmi_watchdog=panic oops=panic load_ramdisk=2 prompt_ramdisk=0 drbd.minor_count=8 systemd.log_level=err ignore_loglevel console=tty0 earlyprintk=ttyS0,115200 console=ttyS0,115200 vga=normal rw rcuperf.shutdown=0 watchdog_thresh=60 [ 0.00] x86/fpu: Supporting XSAVE feature 0x001: 'x87 floating point registers' [ 0.00] x86/fpu: Supporting XSAVE feature 0x002: 'SSE registers' [ 0.00] x86/fpu: Supporting XSAVE feature 0x004: 'AVX registers' [ 0.00] x86/fpu: xstate_offset[2]: 576, xstate_sizes[2]: 256 [ 0.00] x86/fpu: Enabled xstate features 0x7, context size is 832 bytes, using 'standard' format. [ 0.00] BIOS-provided physical RAM map: [ 0.00] BIOS-e820: [mem 0x-0x0009fbff] usable [ 0.00] BIOS-e820: [mem 0x0009fc00-0x0009] reserved [ 0.00] BIOS-e820: [mem 0x000f-0x000f] reserved [ 0.00] BIOS-e820: [mem 0x0010-0xbffd] usable [ 0.00] BIOS-e820: [mem 0xbffe-0xbfff] reserved [ 0.00] BIOS-e820: [mem 0xfeffc000-0xfeff] reserved [ 0.00] BIOS-e820: [mem 0xfffc-0x] reserved [ 0.00] BIOS-e820: [mem 0x0001-0x00023fff] usable [ 0.00] printk: debug: ignoring loglevel setting. [ 0.00] printk: bootconsole [earlyser0] enabled [ 0.00] NX (Execute Disable) protection: active [ 0.00] SMBIOS 2.8 present. [ 0.00] DMI: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1 04/01/2014 [ 0.00] Hypervisor detected: KVM [ 0.00] kvm-clock: Using msrs 4b564d01 and 4b564d00 [ 0.02] kvm-clock: cpu 0, msr 7601001, primary cpu clock [ 0.02] kvm-clock: using sched offset of 2661499940 cycles [ 0.000603] clocksource: kvm-clock: mask: 0x max_cycles: 0x1cd42e4dffb, max_idle_ns: 881590591483 ns [ 0.002261] tsc: Detected 3407.998 MHz processor [ 0.005351] e820: update [mem 0x-0x0fff] usable ==> reserved [ 0.005986] e820: remove [mem 0x000a-0x000f] usable [ 0.006535] last_pfn = 0x24 max_arch_pfn = 0x4 [ 0.007091] MTRR default type: write-back [ 0.007477] MTRR fixed ranges enabled: [ 0.007845] 0-9 write-back [ 0.008191] A-B uncachable [ 0.008536] C-F write-protect [ 0.008906] MTRR variable ranges enabled: [ 0.009293] 0 base 00C000 mask FFC000 uncachable [ 0.009818] 1 disabled [ 0.010064] 2 disabled [ 0.010314] 3 disabled [ 0.010561] 4 disabled [ 0.010822] 5 disabled [ 0.011072] 6
Re: 28307d938f ("percpu: make pcpu_alloc() aware of current gfp .."): BUG: kernel reboot-without-warning in boot stage
On Fri, May 29, 2020 at 01:32:28PM +0100, Filipe Manana wrote:
>
>
> On 29/05/20 08:16, kernel test robot wrote:
> > Greetings,
> >
> > 0day kernel testing robot got the below dmesg and the first bad commit is
> >
> > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> >
> > commit 28307d938fb2e4056ed4c982c06d1503d7719813
> > Author: Filipe Manana
> > AuthorDate: Thu May 7 18:36:10 2020 -0700
> > Commit: Linus Torvalds
> > CommitDate: Thu May 7 19:27:21 2020 -0700
> >
> > percpu: make pcpu_alloc() aware of current gfp context
> >
> > Since 5.7-rc1, on btrfs we have a percpu counter initialization for
> > which we always pass a GFP_KERNEL gfp_t argument (this happens since
> > commit 2992df73268f78 ("btrfs: Implement DREW lock")).
> >
> > That is safe in some contextes but not on others where allowing fs
> > reclaim could lead to a deadlock because we are either holding some
> > btrfs lock needed for a transaction commit or holding a btrfs
> > transaction handle open. Because of that we surround the call to the
> > function that initializes the percpu counter with a NOFS context using
> > memalloc_nofs_save() (this is done at btrfs_init_fs_root()).
> >
> > However it turns out that this is not enough to prevent a possible
> > deadlock because percpu_alloc() determines if it is in an atomic context
> > by looking exclusively at the gfp flags passed to it (GFP_KERNEL in this
> > case) and it is not aware that a NOFS context is set.
> >
> > Because percpu_alloc() thinks it is in a non atomic context it locks the
> > pcpu_alloc_mutex. This can result in a btrfs deadlock when
> > pcpu_balance_workfn() is running, has acquired that mutex and is waiting
> > for reclaim, while the btrfs task that called percpu_counter_init() (and
> > therefore percpu_alloc()) is holding either the btrfs commit_root
> > semaphore or a transaction handle (done fs/btrfs/backref.c:
> > iterate_extent_inodes()), which prevents reclaim from finishing as an
> > attempt to commit the current btrfs transaction will deadlock.
> >
> > Lockdep reports this issue with the following trace:
> >
> > ==
> > WARNING: possible circular locking dependency detected
> > 5.6.0-rc7-btrfs-next-77 #1 Not tainted
> > --
> > kswapd0/91 is trying to acquire lock:
> > 8938a3b3fdc8 (_node->mutex){+.+.}, at:
> > __btrfs_release_delayed_node.part.0+0x3f/0x320 [btrfs]
> >
> > but task is already holding lock:
> > b4f0dbc0 (fs_reclaim){+.+.}, at: __fs_reclaim_acquire+0x5/0x30
> >
> > which lock already depends on the new lock.
> >
> > the existing dependency chain (in reverse order) is:
> >
> > -> #4 (fs_reclaim){+.+.}:
> > fs_reclaim_acquire.part.0+0x25/0x30
> > __kmalloc+0x5f/0x3a0
> > pcpu_create_chunk+0x19/0x230
> > pcpu_balance_workfn+0x56a/0x680
> > process_one_work+0x235/0x5f0
> > worker_thread+0x50/0x3b0
> > kthread+0x120/0x140
> > ret_from_fork+0x3a/0x50
> >
> > -> #3 (pcpu_alloc_mutex){+.+.}:
> > __mutex_lock+0xa9/0xaf0
> > pcpu_alloc+0x480/0x7c0
> > __percpu_counter_init+0x50/0xd0
> > btrfs_drew_lock_init+0x22/0x70 [btrfs]
> > btrfs_get_fs_root+0x29c/0x5c0 [btrfs]
> > resolve_indirect_refs+0x120/0xa30 [btrfs]
> > find_parent_nodes+0x50b/0xf30 [btrfs]
> > btrfs_find_all_leafs+0x60/0xb0 [btrfs]
> > iterate_extent_inodes+0x139/0x2f0 [btrfs]
> > iterate_inodes_from_logical+0xa1/0xe0 [btrfs]
> > btrfs_ioctl_logical_to_ino+0xb4/0x190 [btrfs]
> > btrfs_ioctl+0x165a/0x3130 [btrfs]
> > ksys_ioctl+0x87/0xc0
> > __x64_sys_ioctl+0x16/0x20
> > do_syscall_64+0x5c/0x260
> > entry_SYSCALL_64_after_hwframe+0x49/0xbe
> >
> > -> #2 (_info->commit_root_sem){}:
> > down_write+0x38/0x70
> > btrfs_cache_block_group+0x2ec/0x500 [btrfs]
> > find_free_extent+0xc6a/0x1600 [btrfs]
> > btrfs_reserve_extent+0x9b/0x180 [btrfs]
> > btrfs_alloc_tree_block+0xc1/0x350 [btrfs]
> > alloc_tree_block_no_bg_flush+0x4a/0x60 [btrfs]
> > __btrfs_cow_block+0x122/0x5a0 [btrfs]
> > btrfs_cow_block+0x106/0x240 [btrfs]
> > commit_cowonly_roots+0x55/0x310 [btrfs]
> > btrfs_commit_transaction+0x509/0xb20 [btrfs]
> > sync_filesystem+0x74/0x90
> > generic_shutdown_super+0x22/0x100
> > kill_anon_super+0x14/0x30
> >
Re: 28307d938f ("percpu: make pcpu_alloc() aware of current gfp .."): BUG: kernel reboot-without-warning in boot stage
On 29/05/20 08:16, kernel test robot wrote:
> Greetings,
>
> 0day kernel testing robot got the below dmesg and the first bad commit is
>
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
>
> commit 28307d938fb2e4056ed4c982c06d1503d7719813
> Author: Filipe Manana
> AuthorDate: Thu May 7 18:36:10 2020 -0700
> Commit: Linus Torvalds
> CommitDate: Thu May 7 19:27:21 2020 -0700
>
> percpu: make pcpu_alloc() aware of current gfp context
>
> Since 5.7-rc1, on btrfs we have a percpu counter initialization for
> which we always pass a GFP_KERNEL gfp_t argument (this happens since
> commit 2992df73268f78 ("btrfs: Implement DREW lock")).
>
> That is safe in some contextes but not on others where allowing fs
> reclaim could lead to a deadlock because we are either holding some
> btrfs lock needed for a transaction commit or holding a btrfs
> transaction handle open. Because of that we surround the call to the
> function that initializes the percpu counter with a NOFS context using
> memalloc_nofs_save() (this is done at btrfs_init_fs_root()).
>
> However it turns out that this is not enough to prevent a possible
> deadlock because percpu_alloc() determines if it is in an atomic context
> by looking exclusively at the gfp flags passed to it (GFP_KERNEL in this
> case) and it is not aware that a NOFS context is set.
>
> Because percpu_alloc() thinks it is in a non atomic context it locks the
> pcpu_alloc_mutex. This can result in a btrfs deadlock when
> pcpu_balance_workfn() is running, has acquired that mutex and is waiting
> for reclaim, while the btrfs task that called percpu_counter_init() (and
> therefore percpu_alloc()) is holding either the btrfs commit_root
> semaphore or a transaction handle (done fs/btrfs/backref.c:
> iterate_extent_inodes()), which prevents reclaim from finishing as an
> attempt to commit the current btrfs transaction will deadlock.
>
> Lockdep reports this issue with the following trace:
>
> ==
> WARNING: possible circular locking dependency detected
> 5.6.0-rc7-btrfs-next-77 #1 Not tainted
> --
> kswapd0/91 is trying to acquire lock:
> 8938a3b3fdc8 (_node->mutex){+.+.}, at:
> __btrfs_release_delayed_node.part.0+0x3f/0x320 [btrfs]
>
> but task is already holding lock:
> b4f0dbc0 (fs_reclaim){+.+.}, at: __fs_reclaim_acquire+0x5/0x30
>
> which lock already depends on the new lock.
>
> the existing dependency chain (in reverse order) is:
>
> -> #4 (fs_reclaim){+.+.}:
> fs_reclaim_acquire.part.0+0x25/0x30
> __kmalloc+0x5f/0x3a0
> pcpu_create_chunk+0x19/0x230
> pcpu_balance_workfn+0x56a/0x680
> process_one_work+0x235/0x5f0
> worker_thread+0x50/0x3b0
> kthread+0x120/0x140
> ret_from_fork+0x3a/0x50
>
> -> #3 (pcpu_alloc_mutex){+.+.}:
> __mutex_lock+0xa9/0xaf0
> pcpu_alloc+0x480/0x7c0
> __percpu_counter_init+0x50/0xd0
> btrfs_drew_lock_init+0x22/0x70 [btrfs]
> btrfs_get_fs_root+0x29c/0x5c0 [btrfs]
> resolve_indirect_refs+0x120/0xa30 [btrfs]
> find_parent_nodes+0x50b/0xf30 [btrfs]
> btrfs_find_all_leafs+0x60/0xb0 [btrfs]
> iterate_extent_inodes+0x139/0x2f0 [btrfs]
> iterate_inodes_from_logical+0xa1/0xe0 [btrfs]
> btrfs_ioctl_logical_to_ino+0xb4/0x190 [btrfs]
> btrfs_ioctl+0x165a/0x3130 [btrfs]
> ksys_ioctl+0x87/0xc0
> __x64_sys_ioctl+0x16/0x20
> do_syscall_64+0x5c/0x260
> entry_SYSCALL_64_after_hwframe+0x49/0xbe
>
> -> #2 (_info->commit_root_sem){}:
> down_write+0x38/0x70
> btrfs_cache_block_group+0x2ec/0x500 [btrfs]
> find_free_extent+0xc6a/0x1600 [btrfs]
> btrfs_reserve_extent+0x9b/0x180 [btrfs]
> btrfs_alloc_tree_block+0xc1/0x350 [btrfs]
> alloc_tree_block_no_bg_flush+0x4a/0x60 [btrfs]
> __btrfs_cow_block+0x122/0x5a0 [btrfs]
> btrfs_cow_block+0x106/0x240 [btrfs]
> commit_cowonly_roots+0x55/0x310 [btrfs]
> btrfs_commit_transaction+0x509/0xb20 [btrfs]
> sync_filesystem+0x74/0x90
> generic_shutdown_super+0x22/0x100
> kill_anon_super+0x14/0x30
> btrfs_kill_super+0x12/0x20 [btrfs]
> deactivate_locked_super+0x31/0x70
> cleanup_mnt+0x100/0x160
> task_work_run+0x93/0xc0
> exit_to_usermode_loop+0xf9/0x100
> do_syscall_64+0x20d/0x260
>
