[PATCH RFC v6 00/21] DEPT(Dependency Tracker)

Byungchul Park
2022-05-04T08:49:35Z

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. It's done on v5.18-rc3 tag.

https://github.com/lgebyungchulpark/linux-dept/commits/dept1.20_on_v5.18-rc3

Benifit:

0. Works with all lock primitives.
1. Works with wait_for_completion()/complete().
2. Works with 'wait' on PG_locked.
3. Works with 'wait' on PG_writeback.
4. Works with swait/wakeup.
5. Works with waitqueue.
6. Multiple reports are allowed.
7. Deduplication control on multiple reports.
8. Withstand false positives thanks to 6.
9. Easy to tag any wait/event.

Future work:

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 stack trace.

How to interpret reports:

1. E(event) in each context cannot be triggered because of the
W(wait) that cannot be woken.
2. The stack trace helping find the problematic code is located
in each conext's detail.

Thanks,
Byungchul

---

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 (21):
llist: Move llist_{head,node} definition to types.h
dept: Implement Dept(Dependency Tracker)
dept: Apply Dept to spinlock
dept: Apply Dept to mutex families
dept: Apply Dept to rwlock
dept: Apply Dept to wait_for_completion()/complete()
dept: Apply Dept to seqlock
dept: Apply Dept to rwsem
dept: Add proc knobs to show stats and dependency graph
dept: Introduce split map concept and new APIs for them
dept: Apply Dept to wait/event of PG_{locked,writeback}
dept: Apply SDT to swait
dept: Apply SDT to wait(waitqueue)
locking/lockdep, cpu/hotplus: Use a weaker annotation in AP thread
dept: Distinguish each syscall context from another
dept: Distinguish each work from another
dept: Disable Dept within the wait_bit layer by default
dept: Disable Dept on struct crypto_larval's completion for now
dept: Differentiate onstack maps from others of different tasks in
class
dept: Do not add dependencies between events within scheduler and
sleeps
dept: Unstage wait when tagging a normal sleep wait

arch/arm64/kernel/syscall.c | 2 +
arch/x86/entry/common.c | 4 +
crypto/api.c | 7 +-
include/linux/completion.h | 44 +-
include/linux/dept.h | 596 ++++++++
include/linux/dept_page.h | 78 +
include/linux/dept_sdt.h | 67 +
include/linux/hardirq.h | 3 +
include/linux/irqflags.h | 71 +-
include/linux/llist.h | 8 -
include/linux/lockdep.h | 186 ++-
include/linux/lockdep_types.h | 3 +
include/linux/mutex.h | 22 +
include/linux/page-flags.h | 45 +-
include/linux/pagemap.h | 7 +-
include/linux/percpu-rwsem.h | 4 +-
include/linux/rtmutex.h | 1 +
include/linux/rwlock.h | 42 +
include/linux/rwlock_api_smp.h | 8 +-
include/linux/rwlock_types.h | 1 +
include/linux/rwsem.h | 22 +
include/linux/sched.h | 7 +
include/linux/seqlock.h | 60 +-
include/linux/spinlock.h | 21 +
include/linux/spinlock_types_raw.h | 3 +
include/linux/swait.h | 4 +
include/linux/types.h | 8 +
include/linux/wait.h | 6 +-
init/init_task.c | 2 +
init/main.c | 4 +
kernel/Makefile | 1 +
kernel/cpu.c | 2 +-
kernel/dependency/Makefile | 4 +
kernel/dependency/dept.c | 2938 ++++++++++++++++++++++++++++++++++++
kernel/dependency/dept_hash.h | 10 +
kernel/dependency/dept_internal.h | 26 +
kernel/dependency/dept_object.h | 13 +
kernel/dependency/dept_proc.c | 92 ++
kernel/exit.c | 7 +
kernel/fork.c | 2 +
kernel/locking/lockdep.c | 28 +-
kernel/locking/spinlock_rt.c | 24 +-
kernel/module.c | 2 +
kernel/sched/completion.c | 12 +-
kernel/sched/core.c | 10 +
kernel/sched/swait.c | 10 +
kernel/sched/wait.c | 16 +
kernel/sched/wait_bit.c | 5 +-
kernel/workqueue.c | 3 +
lib/Kconfig.debug | 28 +
mm/filemap.c | 68 +
mm/page_ext.c | 5 +
52 files changed, 4558 insertions(+), 84 deletions(-)
create mode 100644 include/linux/dept.h
create mode 100644 include/linux/dept_page.h
create mode 100644 include/linux/dept_sdt.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

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1.9.1