Re: Report 1 in ext4 and journal based on v5.17-rc1

Byungchul Park
2022-02-18T00:41:41Z

On Thu, Feb 17, 2022 at 01:27:42PM +0000, Matthew Wilcox wrote:
> On Thu, Feb 17, 2022 at 08:10:03PM +0900, Byungchul Park wrote:
> > [ 7.009608] ===================================================
> > [ 7.009613] DEPT: Circular dependency has been detected.
> > [ 7.009614] 5.17.0-rc1-00014-g8a599299c0cb-dirty #30 Tainted: G W
> > [ 7.009616] ---------------------------------------------------
> > [ 7.009617] summary
> > [ 7.009618] ---------------------------------------------------
> > [ 7.009618] *** DEADLOCK ***
> > [ 7.009618]
> > [ 7.009619] context A
> > [ 7.009619] [S] (unknown)(&(bit_wait_table + i)->dmap:0)
>
> Why is the context unknown here? I don't see a way to debug this
> without knowing where we acquired the bit wait lock.

ideal view
------------------

context X context A

request event E to context A ...
write REQUESTEVENT if (can see REQUESTEVENT written)
... notice the request from X [S]
wait for the event [W] ...
write barrier
write WAITSTART
actual wait if (can see REQUESTEVENT written)
consider it's on the way to the event
...
...
finally the event [E]

Dept works with the above view wrt. wait and event. [S] point varies
depending on ways to make context A notice the request so that the event
context A can start. Of course, by making more effort on identifying
each way in the kernel, we can figure out the exact point.

Here, we can also check WAITSTART with a read barrier instead of
REQUESTEVENT in context A conservatively. That's how Dept works.

Dept's view
------------------

context X context A

request event E to context A ...
write REQUESTEVENT if (can see REQUESTEVENT written)
... notice the request from X [S]
wait for the event [W] ...
write barrier
write WAITSTART read barrier
actual wait if (can see WAITSTART written)
consider it's on the way to the event
...
...
finally the event [E]
consider all waits in context A so far
that could see WAITSTART written

Thanks,
Byungchul

> > [ 7.009621] [W] down_write(&ei->i_data_sem:0)
> > [ 7.009623] [E] event(&(bit_wait_table + i)->dmap:0)
> > [ 7.009624]
> > [ 7.009625] context B
> > [ 7.009625] [S] down_read(&ei->i_data_sem:0)
> > [ 7.009626] [W] wait(&(bit_wait_table + i)->dmap:0)
> > [ 7.009627] [E] up_read(&ei->i_data_sem:0)
> > [ 7.009628]
> > [ 7.009629] [S]: start of the event context
> > [ 7.009629] [W]: the wait blocked
> > [ 7.009630] [E]: the event not reachable
> > [ 7.009631] ---------------------------------------------------
> > [ 7.009631] context A's detail
> > [ 7.009632] ---------------------------------------------------
> > [ 7.009632] context A
> > [ 7.009633] [S] (unknown)(&(bit_wait_table + i)->dmap:0)
> > [ 7.009634] [W] down_write(&ei->i_data_sem:0)
> > [ 7.009635] [E] event(&(bit_wait_table + i)->dmap:0)
> > [ 7.009636]
> > [ 7.009636] [S] (unknown)(&(bit_wait_table + i)->dmap:0):
> > [ 7.009638] (N/A)
> > [ 7.009638]
> > [ 7.009639] [W] down_write(&ei->i_data_sem:0):
> > [ 7.009639] ext4_truncate (fs/ext4/inode.c:4187)
> > [ 7.009645] stacktrace:
> > [ 7.009646] down_write (kernel/locking/rwsem.c:1514)
> > [ 7.009648] ext4_truncate (fs/ext4/inode.c:4187)
> > [ 7.009650] ext4_da_write_begin (./include/linux/fs.h:827 fs/ext4/truncate.h:23 fs/ext4/inode.c:2963)
> > [ 7.009652] generic_perform_write (mm/filemap.c:3784)
> > [ 7.009654] ext4_buffered_write_iter (fs/ext4/file.c:269)
> > [ 7.009657] ext4_file_write_iter (fs/ext4/file.c:677)
> > [ 7.009659] new_sync_write (fs/read_write.c:504 (discriminator 1))
> > [ 7.009662] vfs_write (fs/read_write.c:590)
> > [ 7.009663] ksys_write (fs/read_write.c:644)
> > [ 7.009664] do_syscall_64 (arch/x86/entry/common.c:50 arch/x86/entry/common.c:80)
> > [ 7.009667] entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:113)
> > [ 7.009669]
> > [ 7.009670] [E] event(&(bit_wait_table + i)->dmap:0):
> > [ 7.009671] __wake_up_common (kernel/sched/wait.c:108)
> > [ 7.009673] stacktrace:
> > [ 7.009674] dept_event (kernel/dependency/dept.c:2337)
> > [ 7.009677] __wake_up_common (kernel/sched/wait.c:109)
> > [ 7.009678] __wake_up_common_lock (./include/linux/spinlock.h:428 (discriminator 1) kernel/sched/wait.c:141 (discriminator 1))
> > [ 7.009679] __wake_up_bit (kernel/sched/wait_bit.c:127)
> > [ 7.009681] ext4_orphan_del (fs/ext4/orphan.c:282)
> > [ 7.009683] ext4_truncate (fs/ext4/inode.c:4212)
> > [ 7.009685] ext4_da_write_begin (./include/linux/fs.h:827 fs/ext4/truncate.h:23 fs/ext4/inode.c:2963)
> > [ 7.009687] generic_perform_write (mm/filemap.c:3784)
> > [ 7.009688] ext4_buffered_write_iter (fs/ext4/file.c:269)
> > [ 7.009690] ext4_file_write_iter (fs/ext4/file.c:677)
> > [ 7.009692] new_sync_write (fs/read_write.c:504 (discriminator 1))
> > [ 7.009694] vfs_write (fs/read_write.c:590)
> > [ 7.009695] ksys_write (fs/read_write.c:644)
> > [ 7.009696] do_syscall_64 (arch/x86/entry/common.c:50 arch/x86/entry/common.c:80)
> > [ 7.009698] entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:113)
> > [ 7.009700] ---------------------------------------------------
> > [ 7.009700] context B's detail
> > [ 7.009701] ---------------------------------------------------
> > [ 7.009702] context B
> > [ 7.009702] [S] down_read(&ei->i_data_sem:0)
> > [ 7.009703] [W] wait(&(bit_wait_table + i)->dmap:0)
> > [ 7.009704] [E] up_read(&ei->i_data_sem:0)
> > [ 7.009705]
> > [ 7.009706] [S] down_read(&ei->i_data_sem:0):
> > [ 7.009707] ext4_map_blocks (./arch/x86/include/asm/bitops.h:207 ./include/asm-generic/bitops/instrumented-non-atomic.h:135 fs/ext4/ext4.h:1918 fs/ext4/inode.c:562)
> > [ 7.009709] stacktrace:
> > [ 7.009709] down_read (kernel/locking/rwsem.c:1461)
> > [ 7.009711] ext4_map_blocks (./arch/x86/include/asm/bitops.h:207 ./include/asm-generic/bitops/instrumented-non-atomic.h:135 fs/ext4/ext4.h:1918 fs/ext4/inode.c:562)
> > [ 7.009712] ext4_getblk (fs/ext4/inode.c:851)
> > [ 7.009714] ext4_bread (fs/ext4/inode.c:903)
> > [ 7.009715] __ext4_read_dirblock (fs/ext4/namei.c:117)
> > [ 7.009718] dx_probe (fs/ext4/namei.c:789)
> > [ 7.009720] ext4_dx_find_entry (fs/ext4/namei.c:1721)
> > [ 7.009722] __ext4_find_entry (fs/ext4/namei.c:1571)
> > [ 7.009723] ext4_lookup (fs/ext4/namei.c:1770)
> > [ 7.009725] lookup_open (./include/linux/dcache.h:361 fs/namei.c:3310)
> > [ 7.009727] path_openat (fs/namei.c:3401 fs/namei.c:3605)
> > [ 7.009729] do_filp_open (fs/namei.c:3637)
> > [ 7.009731] do_sys_openat2 (fs/open.c:1215)
> > [ 7.009732] do_sys_open (fs/open.c:1231)
> > [ 7.009734] do_syscall_64 (arch/x86/entry/common.c:50 arch/x86/entry/common.c:80)
> > [ 7.009736] entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:113)
> > [ 7.009738]
> > [ 7.009738] [W] wait(&(bit_wait_table + i)->dmap:0):
> > [ 7.009739] prepare_to_wait (kernel/sched/wait.c:275)
> > [ 7.009741] stacktrace:
> > [ 7.009741] __schedule (kernel/sched/sched.h:1318 kernel/sched/sched.h:1616 kernel/sched/core.c:6213)
> > [ 7.009743] schedule (kernel/sched/core.c:6373 (discriminator 1))
> > [ 7.009744] io_schedule (./arch/x86/include/asm/current.h:15 kernel/sched/core.c:8392 kernel/sched/core.c:8418)
> > [ 7.009745] bit_wait_io (./arch/x86/include/asm/current.h:15 kernel/sched/wait_bit.c:210)
> > [ 7.009746] __wait_on_bit (kernel/sched/wait_bit.c:49)
> > [ 7.009748] out_of_line_wait_on_bit (kernel/sched/wait_bit.c:65)
> > [ 7.009749] ext4_read_bh (./arch/x86/include/asm/bitops.h:207 ./include/asm-generic/bitops/instrumented-non-atomic.h:135 ./include/linux/buffer_head.h:120 fs/ext4/super.c:201)
> > [ 7.009752] __read_extent_tree_block (fs/ext4/extents.c:545)
> > [ 7.009754] ext4_find_extent (fs/ext4/extents.c:928)
> > [ 7.009756] ext4_ext_map_blocks (fs/ext4/extents.c:4099)
> > [ 7.009757] ext4_map_blocks (fs/ext4/inode.c:563)
> > [ 7.009759] ext4_getblk (fs/ext4/inode.c:851)
> > [ 7.009760] ext4_bread (fs/ext4/inode.c:903)
> > [ 7.009762] __ext4_read_dirblock (fs/ext4/namei.c:117)
> > [ 7.009764] dx_probe (fs/ext4/namei.c:789)
> > [ 7.009765] ext4_dx_find_entry (fs/ext4/namei.c:1721)
> > [ 7.009767]
> > [ 7.009768] [E] up_read(&ei->i_data_sem:0):
> > [ 7.009769] ext4_map_blocks (fs/ext4/inode.c:593)
> > [ 7.009771] stacktrace:
> > [ 7.009771] up_read (kernel/locking/rwsem.c:1556)
> > [ 7.009774] ext4_map_blocks (fs/ext4/inode.c:593)
> > [ 7.009775] ext4_getblk (fs/ext4/inode.c:851)
> > [ 7.009777] ext4_bread (fs/ext4/inode.c:903)
> > [ 7.009778] __ext4_read_dirblock (fs/ext4/namei.c:117)
> > [ 7.009780] dx_probe (fs/ext4/namei.c:789)
> > [ 7.009782] ext4_dx_find_entry (fs/ext4/namei.c:1721)
> > [ 7.009784] __ext4_find_entry (fs/ext4/namei.c:1571)
> > [ 7.009786] ext4_lookup (fs/ext4/namei.c:1770)
> > [ 7.009788] lookup_open (./include/linux/dcache.h:361 fs/namei.c:3310)
> > [ 7.009789] path_openat (fs/namei.c:3401 fs/namei.c:3605)
> > [ 7.009791] do_filp_open (fs/namei.c:3637)
> > [ 7.009792] do_sys_openat2 (fs/open.c:1215)
> > [ 7.009794] do_sys_open (fs/open.c:1231)
> > [ 7.009795] do_syscall_64 (arch/x86/entry/common.c:50 arch/x86/entry/common.c:80)
> > [ 7.009797] entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:113)
> > [ 7.009799] ---------------------------------------------------
> > [ 7.009800] information that might be helpful
> > [ 7.009800] ---------------------------------------------------
> > [ 7.009801] CPU: 0 PID: 611 Comm: rs:main Q:Reg Tainted: G W 5.17.0-rc1-00014-g8a599299c0cb-dirty #30
> > [ 7.009804] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
> > [ 7.009805] Call Trace:
> > [ 7.009806] <TASK>
> > [ 7.009807] dump_stack_lvl (lib/dump_stack.c:107)
> > [ 7.009809] print_circle (./arch/x86/include/asm/atomic.h:108 ./include/linux/atomic/atomic-instrumented.h:258 kernel/dependency/dept.c:157 kernel/dependency/dept.c:762)
> > [ 7.009812] ? print_circle (kernel/dependency/dept.c:1086)
> > [ 7.009814] cb_check_dl (kernel/dependency/dept.c:1104)
> > [ 7.009815] bfs (kernel/dependency/dept.c:860)
> > [ 7.009818] add_dep (kernel/dependency/dept.c:1423)
> > [ 7.009820] do_event.isra.25 (kernel/dependency/dept.c:1650)
> > [ 7.009822] ? __wake_up_common (kernel/sched/wait.c:108)
> > [ 7.009824] dept_event (kernel/dependency/dept.c:2337)
> > [ 7.009826] __wake_up_common (kernel/sched/wait.c:109)
> > [ 7.009828] __wake_up_common_lock (./include/linux/spinlock.h:428 (discriminator 1) kernel/sched/wait.c:141 (discriminator 1))
> > [ 7.009830] __wake_up_bit (kernel/sched/wait_bit.c:127)
> > [ 7.009832] ext4_orphan_del (fs/ext4/orphan.c:282)
> > [ 7.009835] ? dept_ecxt_exit (./arch/x86/include/asm/current.h:15 kernel/dependency/dept.c:241 kernel/dependency/dept.c:999 kernel/dependency/dept.c:1043 kernel/dependency/dept.c:2478)
> > [ 7.009837] ext4_truncate (fs/ext4/inode.c:4212)
> > [ 7.009839] ext4_da_write_begin (./include/linux/fs.h:827 fs/ext4/truncate.h:23 fs/ext4/inode.c:2963)
> > [ 7.009842] generic_perform_write (mm/filemap.c:3784)
> > [ 7.009845] ext4_buffered_write_iter (fs/ext4/file.c:269)
> > [ 7.009848] ext4_file_write_iter (fs/ext4/file.c:677)
> > [ 7.009851] new_sync_write (fs/read_write.c:504 (discriminator 1))
> > [ 7.009854] vfs_write (fs/read_write.c:590)
> > [ 7.009856] ksys_write (fs/read_write.c:644)
> > [ 7.009857] ? trace_hardirqs_on (kernel/trace/trace_preemptirq.c:65)
> > [ 7.009860] do_syscall_64 (arch/x86/entry/common.c:50 arch/x86/entry/common.c:80)
> > [ 7.009862] entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:113)
> > [ 7.009865] RIP: 0033:0x7f3b160b335d
> > [ 7.009867] Code: e1 20 00 00 75 10 b8 01 00 00 00 0f 05 48 3d 01 f0 ff ff 73 31 c3 48 83 ec 08 e8 ce fa ff ff 48 89 04 24 b8 01 00 00 00 0f 05 <48> 8b 3c 24 48 89 c2 e8 17 fb ff ff 48 89 d0 48 83 c4 08 48 3d 01
> > All code
> > ========
> > 0: e1 20 loope 0x22
> > 2: 00 00 add %al,(%rax)
> > 4: 75 10 jne 0x16
> > 6: b8 01 00 00 00 mov $0x1,%eax
> > b: 0f 05 syscall
> > d: 48 3d 01 f0 ff ff cmp $0xfffffffffffff001,%rax
> > 13: 73 31 jae 0x46
> > 15: c3 retq
> > 16: 48 83 ec 08 sub $0x8,%rsp
> > 1a: e8 ce fa ff ff callq 0xfffffffffffffaed
> > 1f: 48 89 04 24 mov %rax,(%rsp)
> > 23: b8 01 00 00 00 mov $0x1,%eax
> > 28: 0f 05 syscall
> > 2a:* 48 8b 3c 24 mov (%rsp),%rdi <-- trapping instruction
> > 2e: 48 89 c2 mov %rax,%rdx
> > 31: e8 17 fb ff ff callq 0xfffffffffffffb4d
> > 36: 48 89 d0 mov %rdx,%rax
> > 39: 48 83 c4 08 add $0x8,%rsp
> > 3d: 48 rex.W
> > 3e: 3d .byte 0x3d
> > 3f: 01 .byte 0x1
> >
> > Code starting with the faulting instruction
> > ===========================================
> > 0: 48 8b 3c 24 mov (%rsp),%rdi
> > 4: 48 89 c2 mov %rax,%rdx
> > 7: e8 17 fb ff ff callq 0xfffffffffffffb23
> > c: 48 89 d0 mov %rdx,%rax
> > f: 48 83 c4 08 add $0x8,%rsp
> > 13: 48 rex.W
> > 14: 3d .byte 0x3d
> > 15: 01 .byte 0x1
> > [ 7.009869] RSP: 002b:00007f3b1340f180 EFLAGS: 00000293 ORIG_RAX: 0000000000000001
> > [ 7.009871] RAX: ffffffffffffffda RBX: 00007f3b040010a0 RCX: 00007f3b160b335d
> > [ 7.009873] RDX: 0000000000000300 RSI: 00007f3b040010a0 RDI: 0000000000000001
> > [ 7.009874] RBP: 0000000000000000 R08: fffffffffffffa15 R09: fffffffffffffa05
> > [ 7.009875] R10: 0000000000000000 R11: 0000000000000293 R12: 00007f3b04000df0
> > [ 7.009876] R13: 00007f3b1340f1a0 R14: 0000000000000220 R15: 0000000000000300
> > [ 7.009879] </TASK>