Re: Report 2 in ext4 and journal based on v5.17-rc1

Byungchul Park
2022-02-23T00:35:53Z

On Mon, Feb 21, 2022 at 08:02:04PM +0100, Jan Kara wrote:
> On Thu 17-02-22 20:10:04, Byungchul Park wrote:
> > [ 9.008161] ===================================================
> > [ 9.008163] DEPT: Circular dependency has been detected.
> > [ 9.008164] 5.17.0-rc1-00015-gb94f67143867-dirty #2 Tainted: G W
> > [ 9.008166] ---------------------------------------------------
> > [ 9.008167] summary
> > [ 9.008167] ---------------------------------------------------
> > [ 9.008168] *** DEADLOCK ***
> > [ 9.008168]
> > [ 9.008168] context A
> > [ 9.008169] [S] (unknown)(&(&journal->j_wait_transaction_locked)->dmap:0)
> > [ 9.008171] [W] wait(&(&journal->j_wait_commit)->dmap:0)
> > [ 9.008172] [E] event(&(&journal->j_wait_transaction_locked)->dmap:0)
> > [ 9.008173]
> > [ 9.008173] context B
> > [ 9.008174] [S] down_write(mapping.invalidate_lock:0)
> > [ 9.008175] [W] wait(&(&journal->j_wait_transaction_locked)->dmap:0)
> > [ 9.008176] [E] up_write(mapping.invalidate_lock:0)
> > [ 9.008177]
> > [ 9.008178] context C
> > [ 9.008179] [S] (unknown)(&(&journal->j_wait_commit)->dmap:0)
> > [ 9.008180] [W] down_write(mapping.invalidate_lock:0)
> > [ 9.008181] [E] event(&(&journal->j_wait_commit)->dmap:0)
> > [ 9.008181]
> > [ 9.008182] [S]: start of the event context
> > [ 9.008183] [W]: the wait blocked
> > [ 9.008183] [E]: the event not reachable
>
> So what situation is your tool complaining about here? Can you perhaps show
> it here in more common visualization like:

Sure.

> TASK1 TASK2
> does foo, grabs Z
> does X, grabs lock Y
> blocks on Z
> blocks on Y
>
> or something like that? Because I was not able to decipher this from the
> report even after trying for some time...

KJOURNALD2(kthread) TASK1(ksys_write) TASK2(ksys_write)

wait A
--- stuck
wait B
--- stuck
wait C
--- stuck

wake up B wake up C wake up A

where:
A is a wait_queue, j_wait_commit
B is a wait_queue, j_wait_transaction_locked
C is a rwsem, mapping.invalidate_lock

The above is the simplest form. And it's worth noting that Dept focuses
on wait and event itself rather than grabing and releasing things like
lock. The following is the more descriptive form of it.

KJOURNALD2(kthread) TASK1(ksys_write) TASK2(ksys_write)

wait @j_wait_commit
ext4_truncate_failed_write()
down_write(mapping.invalidate_lock)

ext4_truncate()
...
wait @j_wait_transaction_locked

ext_truncate_failed_write()
down_write(mapping.invalidate_lock)

ext4_should_retry_alloc()
...
__jbd2_log_start_commit()
wake_up(j_wait_commit)
jbd2_journal_commit_transaction()
wake_up(j_wait_transaction_locked)
up_write(mapping.invalidate_lock)

I hope this would help you understand the report.

Yeah... This is what Dept complained. And as Ted said, the kthread would
be woken up by another wakeup. So it's not deadlock deadlock. However,
these three threads and any other tasks waiting for any of the events A,
B, C would be struck for a while until the wakeup eventually wakes up
the kthread, kjournald2.

I guess it's not what ext4 is meant to do. Honestly, ext4 and journal
system look so complicated that I'm not convinced tho...

Thanks,
Byungchul

>
> Honza
>
>
>
> > [ 9.008184] ---------------------------------------------------
> > [ 9.008184] context A's detail
> > [ 9.008185] ---------------------------------------------------
> > [ 9.008186] context A
> > [ 9.008186] [S] (unknown)(&(&journal->j_wait_transaction_locked)->dmap:0)
> > [ 9.008187] [W] wait(&(&journal->j_wait_commit)->dmap:0)
> > [ 9.008188] [E] event(&(&journal->j_wait_transaction_locked)->dmap:0)
> > [ 9.008189]
> > [ 9.008190] [S] (unknown)(&(&journal->j_wait_transaction_locked)->dmap:0):
> > [ 9.008191] (N/A)
> > [ 9.008191]
> > [ 9.008192] [W] wait(&(&journal->j_wait_commit)->dmap:0):
> > [ 9.008193] prepare_to_wait (kernel/sched/wait.c:275)
> > [ 9.008197] stacktrace:
> > [ 9.008198] __schedule (kernel/sched/sched.h:1318 kernel/sched/sched.h:1616 kernel/sched/core.c:6213)
> > [ 9.008200] schedule (kernel/sched/core.c:6373 (discriminator 1))
> > [ 9.008201] kjournald2 (fs/jbd2/journal.c:250)
> > [ 9.008203] kthread (kernel/kthread.c:377)
> > [ 9.008206] ret_from_fork (arch/x86/entry/entry_64.S:301)
> > [ 9.008209]
> > [ 9.008209] [E] event(&(&journal->j_wait_transaction_locked)->dmap:0):
> > [ 9.008210] __wake_up_common (kernel/sched/wait.c:108)
> > [ 9.008212] stacktrace:
> > [ 9.008213] dept_event (kernel/dependency/dept.c:2337)
> > [ 9.008215] __wake_up_common (kernel/sched/wait.c:109)
> > [ 9.008217] __wake_up_common_lock (./include/linux/spinlock.h:428 (discriminator 1) kernel/sched/wait.c:141 (discriminator 1))
> > [ 9.008218] jbd2_journal_commit_transaction (fs/jbd2/commit.c:583)
> > [ 9.008221] kjournald2 (fs/jbd2/journal.c:214 (discriminator 3))
> > [ 9.008223] kthread (kernel/kthread.c:377)
> > [ 9.008224] ret_from_fork (arch/x86/entry/entry_64.S:301)
> > [ 9.008226] ---------------------------------------------------
> > [ 9.008226] context B's detail
> > [ 9.008227] ---------------------------------------------------
> > [ 9.008228] context B
> > [ 9.008228] [S] down_write(mapping.invalidate_lock:0)
> > [ 9.008229] [W] wait(&(&journal->j_wait_transaction_locked)->dmap:0)
> > [ 9.008230] [E] up_write(mapping.invalidate_lock:0)
> > [ 9.008231]
> > [ 9.008232] [S] down_write(mapping.invalidate_lock:0):
> > [ 9.008233] ext4_da_write_begin (fs/ext4/truncate.h:21 fs/ext4/inode.c:2963)
> > [ 9.008237] stacktrace:
> > [ 9.008237] down_write (kernel/locking/rwsem.c:1514)
> > [ 9.008239] ext4_da_write_begin (fs/ext4/truncate.h:21 fs/ext4/inode.c:2963)
> > [ 9.008241] generic_perform_write (mm/filemap.c:3784)
> > [ 9.008243] ext4_buffered_write_iter (fs/ext4/file.c:269)
> > [ 9.008245] ext4_file_write_iter (fs/ext4/file.c:677)
> > [ 9.008247] new_sync_write (fs/read_write.c:504 (discriminator 1))
> > [ 9.008250] vfs_write (fs/read_write.c:590)
> > [ 9.008251] ksys_write (fs/read_write.c:644)
> > [ 9.008253] do_syscall_64 (arch/x86/entry/common.c:50 arch/x86/entry/common.c:80)
> > [ 9.008255] entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:113)
> > [ 9.008258]
> > [ 9.008258] [W] wait(&(&journal->j_wait_transaction_locked)->dmap:0):
> > [ 9.008259] prepare_to_wait (kernel/sched/wait.c:275)
> > [ 9.008261] stacktrace:
> > [ 9.008261] __schedule (kernel/sched/sched.h:1318 kernel/sched/sched.h:1616 kernel/sched/core.c:6213)
> > [ 9.008263] schedule (kernel/sched/core.c:6373 (discriminator 1))
> > [ 9.008264] wait_transaction_locked (fs/jbd2/transaction.c:184)
> > [ 9.008266] add_transaction_credits (fs/jbd2/transaction.c:248 (discriminator 3))
> > [ 9.008267] start_this_handle (fs/jbd2/transaction.c:427)
> > [ 9.008269] jbd2__journal_start (fs/jbd2/transaction.c:526)
> > [ 9.008271] __ext4_journal_start_sb (fs/ext4/ext4_jbd2.c:105)
> > [ 9.008273] ext4_truncate (fs/ext4/inode.c:4164)
> > [ 9.008274] ext4_da_write_begin (./include/linux/fs.h:827 fs/ext4/truncate.h:23 fs/ext4/inode.c:2963)
> > [ 9.008276] generic_perform_write (mm/filemap.c:3784)
> > [ 9.008277] ext4_buffered_write_iter (fs/ext4/file.c:269)
> > [ 9.008279] ext4_file_write_iter (fs/ext4/file.c:677)
> > [ 9.008281] new_sync_write (fs/read_write.c:504 (discriminator 1))
> > [ 9.008283] vfs_write (fs/read_write.c:590)
> > [ 9.008284] ksys_write (fs/read_write.c:644)
> > [ 9.008285] do_syscall_64 (arch/x86/entry/common.c:50 arch/x86/entry/common.c:80)
> > [ 9.008287]
> > [ 9.008288] [E] up_write(mapping.invalidate_lock:0):
> > [ 9.008288] ext4_da_get_block_prep (fs/ext4/inode.c:1795 fs/ext4/inode.c:1829)
> > [ 9.008291] ---------------------------------------------------
> > [ 9.008291] context C's detail
> > [ 9.008292] ---------------------------------------------------
> > [ 9.008292] context C
> > [ 9.008293] [S] (unknown)(&(&journal->j_wait_commit)->dmap:0)
> > [ 9.008294] [W] down_write(mapping.invalidate_lock:0)
> > [ 9.008295] [E] event(&(&journal->j_wait_commit)->dmap:0)
> > [ 9.008296]
> > [ 9.008297] [S] (unknown)(&(&journal->j_wait_commit)->dmap:0):
> > [ 9.008298] (N/A)
> > [ 9.008298]
> > [ 9.008299] [W] down_write(mapping.invalidate_lock:0):
> > [ 9.008299] ext4_da_write_begin (fs/ext4/truncate.h:21 fs/ext4/inode.c:2963)
> > [ 9.008302] stacktrace:
> > [ 9.008302] down_write (kernel/locking/rwsem.c:1514)
> > [ 9.008304] ext4_da_write_begin (fs/ext4/truncate.h:21 fs/ext4/inode.c:2963)
> > [ 9.008305] generic_perform_write (mm/filemap.c:3784)
> > [ 9.008307] ext4_buffered_write_iter (fs/ext4/file.c:269)
> > [ 9.008309] ext4_file_write_iter (fs/ext4/file.c:677)
> > [ 9.008311] new_sync_write (fs/read_write.c:504 (discriminator 1))
> > [ 9.008312] vfs_write (fs/read_write.c:590)
> > [ 9.008314] ksys_write (fs/read_write.c:644)
> > [ 9.008315] do_syscall_64 (arch/x86/entry/common.c:50 arch/x86/entry/common.c:80)
> > [ 9.008316] entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:113)
> > [ 9.008318]
> > [ 9.008319] [E] event(&(&journal->j_wait_commit)->dmap:0):
> > [ 9.008320] __wake_up_common (kernel/sched/wait.c:108)
> > [ 9.008321] stacktrace:
> > [ 9.008322] __wake_up_common (kernel/sched/wait.c:109)
> > [ 9.008323] __wake_up_common_lock (./include/linux/spinlock.h:428 (discriminator 1) kernel/sched/wait.c:141 (discriminator 1))
> > [ 9.008324] __jbd2_log_start_commit (fs/jbd2/journal.c:508)
> > [ 9.008326] jbd2_log_start_commit (fs/jbd2/journal.c:527)
> > [ 9.008327] __jbd2_journal_force_commit (fs/jbd2/journal.c:560)
> > [ 9.008329] jbd2_journal_force_commit_nested (fs/jbd2/journal.c:583)
> > [ 9.008331] ext4_should_retry_alloc (fs/ext4/balloc.c:670 (discriminator 3))
> > [ 9.008332] ext4_da_write_begin (fs/ext4/inode.c:2965 (discriminator 1))
> > [ 9.008334] generic_perform_write (mm/filemap.c:3784)
> > [ 9.008335] ext4_buffered_write_iter (fs/ext4/file.c:269)
> > [ 9.008337] ext4_file_write_iter (fs/ext4/file.c:677)
> > [ 9.008339] new_sync_write (fs/read_write.c:504 (discriminator 1))
> > [ 9.008341] vfs_write (fs/read_write.c:590)
> > [ 9.008342] ksys_write (fs/read_write.c:644)
> > [ 9.008343] do_syscall_64 (arch/x86/entry/common.c:50 arch/x86/entry/common.c:80)
> > [ 9.008345] entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:113)
> > [ 9.008347] ---------------------------------------------------
> > [ 9.008348] information that might be helpful
> > [ 9.008348] ---------------------------------------------------
> > [ 9.008349] CPU: 0 PID: 89 Comm: jbd2/sda1-8 Tainted: G W 5.17.0-rc1-00015-gb94f67143867-dirty #2
> > [ 9.008352] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
> > [ 9.008353] Call Trace:
> > [ 9.008354] <TASK>
> > [ 9.008355] dump_stack_lvl (lib/dump_stack.c:107)
> > [ 9.008358] 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)
> > [ 9.008360] ? print_circle (kernel/dependency/dept.c:1086)
> > [ 9.008362] cb_check_dl (kernel/dependency/dept.c:1104)
> > [ 9.008364] bfs (kernel/dependency/dept.c:860)
> > [ 9.008366] add_dep (kernel/dependency/dept.c:1423)
> > [ 9.008368] do_event.isra.25 (kernel/dependency/dept.c:1651)
> > [ 9.008370] ? __wake_up_common (kernel/sched/wait.c:108)
> > [ 9.008372] dept_event (kernel/dependency/dept.c:2337)
> > [ 9.008374] __wake_up_common (kernel/sched/wait.c:109)
> > [ 9.008376] __wake_up_common_lock (./include/linux/spinlock.h:428 (discriminator 1) kernel/sched/wait.c:141 (discriminator 1))
> > [ 9.008379] jbd2_journal_commit_transaction (fs/jbd2/commit.c:583)
> > [ 9.008381] ? arch_stack_walk (arch/x86/kernel/stacktrace.c:24)
> > [ 9.008385] ? ret_from_fork (arch/x86/entry/entry_64.S:301)
> > [ 9.008387] ? dept_enable_hardirq (./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:1843)
> > [ 9.008389] ? _raw_spin_unlock_irqrestore (./arch/x86/include/asm/irqflags.h:45 ./arch/x86/include/asm/irqflags.h:80 ./arch/x86/include/asm/irqflags.h:138 ./include/linux/spinlock_api_smp.h:151 kernel/locking/spinlock.c:194)
> > [ 9.008392] ? _raw_spin_unlock_irqrestore (./arch/x86/include/asm/preempt.h:103 ./include/linux/spinlock_api_smp.h:152 kernel/locking/spinlock.c:194)
> > [ 9.008394] ? try_to_del_timer_sync (kernel/time/timer.c:1239)
> > [ 9.008396] kjournald2 (fs/jbd2/journal.c:214 (discriminator 3))
> > [ 9.008398] ? prepare_to_wait_exclusive (kernel/sched/wait.c:431)
> > [ 9.008400] ? commit_timeout (fs/jbd2/journal.c:173)
> > [ 9.008402] kthread (kernel/kthread.c:377)
> > [ 9.008404] ? kthread_complete_and_exit (kernel/kthread.c:332)
> > [ 9.008407] ret_from_fork (arch/x86/entry/entry_64.S:301)
> > [ 9.008410] </TASK>
> --
> Jan Kara <jack@suse.com>
> SUSE Labs, CR