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Message-Id: <20250513100730.12664-1-byungchul@sk.com>
Date: Tue, 13 May 2025 19:06:47 +0900
From: Byungchul Park <byungchul@...com>
To: linux-kernel@...r.kernel.org
Cc: kernel_team@...ynix.com,
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Subject: [PATCH v15 00/43] DEPT(DEPendency Tracker)
I'm happy to see that dept reported a real problem in practice. See:
https://lore.kernel.org/lkml/6383cde5-cf4b-facf-6e07-1378a485657d@I-love.SAKURA.ne.jp/#t
https://lore.kernel.org/lkml/1674268856-31807-1-git-send-email-byungchul.park@lge.com/
I added a document describing dept, that would help you understand what
dept is and how dept works. You can use dept just with CONFIG_DEPT on
and by checking dmesg in runtime.
There are still false positives here and there and some of those are
already in progress to suppress and the efforts are essencial until it
gets more stable as lockdep experienced.
It's worth noting that EXPERIMENTAL in Kconfig is tagged.
---
Hi Linus and folks,
I've been developing a tool for detecting deadlock possibilities by
tracking wait/event rather than lock acquisition order to try to cover
all synchonization machanisms.
Benefits:
0. Works with all lock primitives.
1. Works with wait_for_completion()/complete().
2. Works with PG_locked.
3. Works with swait/wakeup.
4. Works with waitqueue.
5. Works with wait_bit.
6. Multiple reports are allowed.
7. Deduplication control on multiple reports.
8. Withstand false positives thanks to 7.
9. Easy to tag any wait/event.
Future works:
0. To make it more stable.
1. To separates dept from lockdep.
2. To improves performance in terms of time and space.
3. To use dept as a dependency engine for lockdep.
4. To add any missing tags of wait/event in the kernel.
5. To deduplicate memory space for stack traces.
How to interpret reports:
(See the document in this patchset for more detail.)
[S] the start of the event context
[W] the wait disturbing the event from being triggered
[E] the event that cannot be reachable
Thanks.
Byungchul
---
Changes from v14:
1. Rebase on the current latest, v6.15-rc6.
2. Refactor dept code.
3. With multi event sites for a single wait, even if an event
forms a circular dependency, the event can be recovered by
other event(or wake up) paths. Even though informing the
circular dependency is worthy but it should be suppressed
once informing it, if it doesn't lead an actual deadlock. So
introduce APIs to annotate the relationship between event
site and recover site, that are, event_site() and
dept_recover_event().
4. wait_for_completion() worked with dept map embedded in struct
completion. However, it generates a few false positves since
all the waits using the instance of struct completion, share
the map and key. To avoid the false positves, make it not to
share the map and key but each wait_for_completion() caller
have its own key by default. Of course, external maps also
can be used if needed.
5. Fix a bug about hardirq on/off tracing.
6. Implement basic unit test for dept.
7. Add more supports for dma fence synchronization.
8. Add emergency stop of dept e.g. on panic().
9. Fix false positives by mmu_notifier_invalidate_*().
10. Fix recursive call bug by DEPT_WARN_*() and DEPT_STOP().
11. Fix trivial bugs in DEPT_WARN_*() and DEPT_STOP().
12. Fix a bug that a spin lock, dept_pool_spin, is used in
both contexts of irq disabled and enabled without irq
disabled.
13. Suppress reports with classes, any of that already have
been reported, even though they have different chains but
being barely meaningful.
14. Print stacktrace of the wait that an event is now waking up,
not only stacktrace of the event.
15. Make dept aware of lockdep_cmp_fn() that is used to avoid
false positives in lockdep so that dept can also avoid them.
16. Do do_event() only if there are no ecxts have been
delimited.
17. Fix a bug that was not synchronized for stage_m in struct
dept_task, using a spin lock, dept_task()->stage_lock.
18. Fix a bug that dept didn't handle the case that multiple
ttwus for a single waiter can be called at the same time
e.i. a race issue.
19. Distinguish each kernel context from others, not only by
system call but also by user oriented fault so that dept can
work with more accuracy information about kernel context.
That helps to avoid a few false positives.
20. Limit dept's working to x86_64 and arm64.
Changes from v13:
1. Rebase on the current latest version, v6.9-rc7.
2. Add 'dept' documentation describing dept APIs.
Changes from v12:
1. Refine the whole document for dept.
2. Add 'Interpret dept report' section in the document, using a
deadlock report obtained in practice. Hope this version of
document helps guys understand dept better.
https://lore.kernel.org/lkml/6383cde5-cf4b-facf-6e07-1378a485657d@I-love.SAKURA.ne.jp/#t
https://lore.kernel.org/lkml/1674268856-31807-1-git-send-email-byungchul.park@lge.com/
Changes from v11:
1. Add 'dept' documentation describing the concept of dept.
2. Rewrite the commit messages of the following commits for
using weaker lockdep annotation, for better description.
fs/jbd2: Use a weaker annotation in journal handling
cpu/hotplug: Use a weaker annotation in AP thread
(feedbacked by Thomas Gleixner)
Changes from v10:
1. Fix noinstr warning when building kernel source.
2. dept has been reporting some false positives due to the folio
lock's unfairness. Reflect it and make dept work based on
dept annotaions instead of just wait and wake up primitives.
3. Remove the support for PG_writeback while working on 2. I
will add the support later if needed.
4. dept didn't print stacktrace for [S] if the participant of a
deadlock is not lock mechanism but general wait and event.
However, it made hard to interpret the report in that case.
So add support to print stacktrace of the requestor who asked
the event context to run - usually a waiter of the event does
it just before going to wait state.
5. Give up tracking raw_local_irq_{disable,enable}() since it
totally messed up dept's irq tracking. So make it work in the
same way as lockdep does. I will consider it once any false
positives by those are observed again.
6. Change the manual rwsem_acquire_read(->j_trans_commit_map)
annotation in fs/jbd2/transaction.c to the try version so
that it works as much as it exactly needs.
7. Remove unnecessary 'inline' keyword in dept.c and add
'__maybe_unused' to a needed place.
Changes from v9:
1. Fix a bug. SDT tracking didn't work well because of my big
mistake that I should've used waiter's map to indentify its
class but it had been working with waker's one. FYI,
PG_locked and PG_writeback weren't affected. They still
worked well. (reported by YoungJun)
Changes from v8:
1. Fix build error by adding EXPORT_SYMBOL(PG_locked_map) and
EXPORT_SYMBOL(PG_writeback_map) for kernel module build -
appologize for that. (reported by kernel test robot)
2. Fix build error by removing header file's circular dependency
that was caused by "atomic.h", "kernel.h" and "irqflags.h",
which I introduced - appolgize for that. (reported by kernel
test robot)
Changes from v7:
1. Fix a bug that cannot track rwlock dependency properly,
introduced in v7. (reported by Boqun and lockdep selftest)
2. Track wait/event of PG_{locked,writeback} more aggressively
assuming that when a bit of PG_{locked,writeback} is cleared
there might be waits on the bit. (reported by Linus, Hillf
and syzbot)
3. Fix and clean bad style code e.i. unnecessarily introduced
a randome pattern and so on. (pointed out by Linux)
4. Clean code for applying dept to wait_for_completion().
Changes from v6:
1. Tie to task scheduler code to track sleep and try_to_wake_up()
assuming sleeps cause waits, try_to_wake_up()s would be the
events that those are waiting for, of course with proper dept
annotations, sdt_might_sleep_weak(), sdt_might_sleep_strong()
and so on. For these cases, class is classified at sleep
entrance rather than the synchronization initialization code.
Which would extremely reduce false alarms.
2. Remove the dept associated instance in each page struct for
tracking dependencies by PG_locked and PG_writeback thanks to
the 1. work above.
3. Introduce CONFIG_dept_AGGRESIVE_TIMEOUT_WAIT to suppress
reports that waits with timeout set are involved, for those
who don't like verbose reporting.
4. Add a mechanism to refill the internal memory pools on
running out so that dept could keep working as long as free
memory is available in the system.
5. Re-enable tracking hashed-waitqueue wait. That's going to no
longer generate false positives because class is classified
at sleep entrance rather than the waitqueue initailization.
6. Refactor to make it easier to port onto each new version of
the kernel.
7. Apply dept to dma fence.
8. Do trivial optimizaitions.
Changes from v5:
1. Use just pr_warn_once() rather than WARN_ONCE() on the lack
of internal resources because WARN_*() printing stacktrace is
too much for informing the lack. (feedback from Ted, Hyeonggon)
2. Fix trivial bugs like missing initializing a struct before
using it.
3. Assign a different class per task when handling onstack
variables for waitqueue or the like. Which makes dept
distinguish between onstack variables of different tasks so
as to prevent false positives. (reported by Hyeonggon)
4. Make dept aware of even raw_local_irq_*() to prevent false
positives. (reported by Hyeonggon)
5. Don't consider dependencies between the events that might be
triggered within __schedule() and the waits that requires
__schedule(), real ones. (reported by Hyeonggon)
6. Unstage the staged wait that has prepare_to_wait_event()'ed
*and* yet to get to __schedule(), if we encounter __schedule()
in-between for another sleep, which is possible if e.g. a
mutex_lock() exists in 'condition' of ___wait_event().
7. Turn on CONFIG_PROVE_LOCKING when CONFIG_DEPT is on, to rely
on the hardirq and softirq entrance tracing to make dept more
portable for now.
Changes from v4:
1. Fix some bugs that produce false alarms.
2. Distinguish each syscall context from another *for arm64*.
3. Make it not warn it but just print it in case dept ring
buffer gets exhausted. (feedback from Hyeonggon)
4. Explicitely describe "EXPERIMENTAL" and "dept might produce
false positive reports" in Kconfig. (feedback from Ted)
Changes from v3:
1. dept shouldn't create dependencies between different depths
of a class that were indicated by *_lock_nested(). dept
normally doesn't but it does once another lock class comes
in. So fixed it. (feedback from Hyeonggon)
2. dept considered a wait as a real wait once getting to
__schedule() even if it has been set to TASK_RUNNING by wake
up sources in advance. Fixed it so that dept doesn't consider
the case as a real wait. (feedback from Jan Kara)
3. Stop tracking dependencies with a map once the event
associated with the map has been handled. dept will start to
work with the map again, on the next sleep.
Changes from v2:
1. Disable dept on bit_wait_table[] in sched/wait_bit.c
reporting a lot of false positives, which is my fault.
Wait/event for bit_wait_table[] should've been tagged in a
higher layer for better work, which is a future work.
(feedback from Jan Kara)
2. Disable dept on crypto_larval's completion to prevent a false
positive.
Changes from v1:
1. Fix coding style and typo. (feedback from Steven)
2. Distinguish each work context from another in workqueue.
3. Skip checking lock acquisition with nest_lock, which is about
correct lock usage that should be checked by lockdep.
Changes from RFC(v0):
1. Prevent adding a wait tag at prepare_to_wait() but __schedule().
(feedback from Linus and Matthew)
2. Use try version at lockdep_acquire_cpus_lock() annotation.
3. Distinguish each syscall context from another.
Byungchul Park (43):
llist: move llist_{head,node} definition to types.h
dept: implement DEPT(DEPendency Tracker)
dept: add single event dependency tracker APIs
dept: add lock dependency tracker APIs
dept: tie to lockdep and IRQ tracing
dept: add proc knobs to show stats and dependency graph
dept: distinguish each kernel context from another
x86_64, dept: add support CONFIG_ARCH_HAS_DEPT_SUPPORT to x86_64
arm64, dept: add support CONFIG_ARCH_HAS_DEPT_SUPPORT to arm64
dept: distinguish each work from another
dept: add a mechanism to refill the internal memory pools on running
out
dept: record the latest one out of consecutive waits of the same class
dept: apply sdt_might_sleep_{start,end}() to
wait_for_completion()/complete()
dept: apply sdt_might_sleep_{start,end}() to swait
dept: apply sdt_might_sleep_{start,end}() to waitqueue wait
dept: apply sdt_might_sleep_{start,end}() to hashed-waitqueue wait
dept: apply sdt_might_sleep_{start,end}() to dma fence
dept: track timeout waits separately with a new Kconfig
dept: apply timeout consideration to wait_for_completion()/complete()
dept: apply timeout consideration to swait
dept: apply timeout consideration to waitqueue wait
dept: apply timeout consideration to hashed-waitqueue wait
dept: apply timeout consideration to dma fence wait
dept: make dept able to work with an external wgen
dept: track PG_locked with dept
dept: print staged wait's stacktrace on report
locking/lockdep: prevent various lockdep assertions when
lockdep_off()'ed
dept: suppress reports with classes that have been already reported
dept: add documentation for dept
cpu/hotplug: use a weaker annotation in AP thread
fs/jbd2: use a weaker annotation in journal handling
dept: assign dept map to mmu notifier invalidation synchronization
dept: assign unique dept_key to each distinct dma fence caller
dept: make dept aware of lockdep_set_lock_cmp_fn() annotation
dept: make dept stop from working on debug_locks_off()
i2c: rename wait_for_completion callback to wait_for_completion_cb
dept: assign unique dept_key to each distinct wait_for_completion()
caller
completion, dept: introduce init_completion_dmap() API
dept: introduce a new type of dependency tracking between multi event
sites
dept: add module support for struct dept_event_site and
dept_event_site_dep
dept: introduce event_site() to disable event tracking if it's
recoverable
dept: implement a basic unit test for dept
dept: call dept_hardirqs_off() in local_irq_*() regardless of irq
state
Documentation/dependency/dept.txt | 735 ++++++
Documentation/dependency/dept_api.txt | 117 +
arch/arm64/Kconfig | 1 +
arch/arm64/kernel/syscall.c | 7 +
arch/arm64/mm/fault.c | 7 +
arch/x86/Kconfig | 1 +
arch/x86/entry/syscall_64.c | 7 +
arch/x86/mm/fault.c | 7 +
drivers/dma-buf/dma-fence.c | 17 +-
drivers/i2c/algos/i2c-algo-pca.c | 2 +-
drivers/i2c/busses/i2c-pca-isa.c | 2 +-
drivers/i2c/busses/i2c-pca-platform.c | 2 +-
fs/jbd2/transaction.c | 2 +-
include/asm-generic/vmlinux.lds.h | 13 +-
include/linux/completion.h | 124 +-
include/linux/dept.h | 625 +++++
include/linux/dept_ldt.h | 77 +
include/linux/dept_sdt.h | 67 +
include/linux/dept_unit_test.h | 67 +
include/linux/dma-fence.h | 74 +-
include/linux/hardirq.h | 3 +
include/linux/i2c-algo-pca.h | 2 +-
include/linux/irqflags.h | 21 +-
include/linux/llist.h | 8 -
include/linux/local_lock_internal.h | 1 +
include/linux/lockdep.h | 105 +-
include/linux/lockdep_types.h | 3 +
include/linux/mm_types.h | 2 +
include/linux/mmu_notifier.h | 26 +
include/linux/module.h | 5 +
include/linux/mutex.h | 1 +
include/linux/page-flags.h | 125 +-
include/linux/pagemap.h | 7 +-
include/linux/percpu-rwsem.h | 2 +-
include/linux/rtmutex.h | 1 +
include/linux/rwlock_types.h | 1 +
include/linux/rwsem.h | 1 +
include/linux/sched.h | 120 +-
include/linux/seqlock.h | 2 +-
include/linux/spinlock_types_raw.h | 3 +
include/linux/srcu.h | 2 +-
include/linux/swait.h | 3 +
include/linux/types.h | 8 +
include/linux/wait.h | 3 +
include/linux/wait_bit.h | 3 +
init/init_task.c | 2 +
init/main.c | 2 +
kernel/Makefile | 1 +
kernel/cpu.c | 2 +-
kernel/dependency/Makefile | 5 +
kernel/dependency/dept.c | 3510 +++++++++++++++++++++++++
kernel/dependency/dept_hash.h | 10 +
kernel/dependency/dept_internal.h | 64 +
kernel/dependency/dept_object.h | 13 +
kernel/dependency/dept_proc.c | 93 +
kernel/dependency/dept_unit_test.c | 173 ++
kernel/exit.c | 1 +
kernel/fork.c | 2 +
kernel/locking/lockdep.c | 33 +
kernel/module/main.c | 19 +
kernel/sched/completion.c | 62 +-
kernel/sched/core.c | 8 +
kernel/workqueue.c | 3 +
lib/Kconfig.debug | 51 +
lib/debug_locks.c | 2 +
lib/locking-selftest.c | 2 +
mm/filemap.c | 26 +
mm/mm_init.c | 2 +
mm/mmu_notifier.c | 31 +-
69 files changed, 6404 insertions(+), 125 deletions(-)
create mode 100644 Documentation/dependency/dept.txt
create mode 100644 Documentation/dependency/dept_api.txt
create mode 100644 include/linux/dept.h
create mode 100644 include/linux/dept_ldt.h
create mode 100644 include/linux/dept_sdt.h
create mode 100644 include/linux/dept_unit_test.h
create mode 100644 kernel/dependency/Makefile
create mode 100644 kernel/dependency/dept.c
create mode 100644 kernel/dependency/dept_hash.h
create mode 100644 kernel/dependency/dept_internal.h
create mode 100644 kernel/dependency/dept_object.h
create mode 100644 kernel/dependency/dept_proc.c
create mode 100644 kernel/dependency/dept_unit_test.c
base-commit: 82f2b0b97b36ee3fcddf0f0780a9a0825d52fec3
--
2.17.1
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