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 v5.17-rc1 tag.
https://github.com/lgebyungchulpark/linux-dept/commits/dept1.12_on_v5.17-rc1
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.
I've got several reports from the tool. Some of them look like false alarms and some others look like real deadlock possibility. Because of my unfamiliarity of the domain, it's hard to confirm if it's a real one. Let me add the reports on this email thread.
How to interpret the report is:
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.
Changes from RFC:
1. Prevent adding a wait tag at prepare_to_wait() but __schedule(). 2. Use try version at lockdep_acquire_cpus_lock() annotation. 3. Distinguish each syscall context from another.
Thanks, Byungchul
Byungchul Park (16): llist: Move llist_{head,node} definition to types.h dept: Implement Dept(Dependency Tracker) dept: Embed Dept data in Lockdep 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
include/linux/completion.h | 42 +- include/linux/dept.h | 523 +++++++ include/linux/dept_page.h | 78 ++ include/linux/dept_sdt.h | 62 + include/linux/hardirq.h | 3 + include/linux/irqflags.h | 33 +- include/linux/llist.h | 8 - include/linux/lockdep.h | 156 ++- include/linux/lockdep_types.h | 3 + include/linux/mutex.h | 31 + include/linux/page-flags.h | 45 +- include/linux/pagemap.h | 7 +- include/linux/percpu-rwsem.h | 10 +- include/linux/rtmutex.h | 7 + include/linux/rwlock.h | 48 + include/linux/rwlock_api_smp.h | 8 +- include/linux/rwlock_types.h | 7 + include/linux/rwsem.h | 31 + include/linux/sched.h | 7 + include/linux/seqlock.h | 59 +- include/linux/spinlock.h | 24 + include/linux/spinlock_types_raw.h | 13 + 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 | 5 + kernel/dependency/dept.c | 2702 ++++++++++++++++++++++++++++++++++++ kernel/dependency/dept_hash.h | 10 + kernel/dependency/dept_internal.h | 26 + kernel/dependency/dept_object.h | 13 + kernel/dependency/dept_proc.c | 93 ++ kernel/entry/common.c | 3 + kernel/exit.c | 1 + kernel/fork.c | 2 + kernel/locking/lockdep.c | 12 +- kernel/module.c | 2 + kernel/sched/completion.c | 12 +- kernel/sched/core.c | 3 + kernel/sched/swait.c | 10 + kernel/sched/wait.c | 16 + kernel/softirq.c | 6 +- kernel/trace/trace_preemptirq.c | 19 +- lib/Kconfig.debug | 21 + mm/filemap.c | 68 + mm/page_ext.c | 5 + 49 files changed, 4204 insertions(+), 57 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