On Fri, Mar 04, 2022 at 04:06:19PM +0900, Byungchul Park wrote: > 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/dept1.14_on_v5.17-rc1 > Small feedback unrelated to thread: I'm not sure "Need to expand the ring buffer" is something to call WARN(). Is this stack trace useful for something? ======== Hello Byungchul. These are two warnings of DEPT on system. Both cases look similar. In what case DEPT says (unknown)? I'm not sure we can properly debug this. =================================================== DEPT: Circular dependency has been detected. 5.17.0-rc1+ #3 Tainted: G W --------------------------------------------------- summary --------------------------------------------------- *** AA DEADLOCK *** context A [S] (unknown)(&vfork:0) [W] wait_for_completion_killable(&vfork:0) [E] complete(&vfork:0) [S]: start of the event context [W]: the wait blocked [E]: the event not reachable --------------------------------------------------- context A's detail --------------------------------------------------- context A [S] (unknown)(&vfork:0) [W] wait_for_completion_killable(&vfork:0) [E] complete(&vfork:0) [S] (unknown)(&vfork:0): (N/A) [W] wait_for_completion_killable(&vfork:0): [<ffffffc00802204c>] kernel_clone+0x25c/0x2b8 stacktrace: dept_wait+0x74/0x88 wait_for_completion_killable+0x60/0xa0 kernel_clone+0x25c/0x2b8 __do_sys_clone+0x5c/0x74 __arm64_sys_clone+0x18/0x20 invoke_syscall.constprop.0+0x78/0xc4 do_el0_svc+0x98/0xd0 el0_svc+0x44/0xe4 el0t_64_sync_handler+0xb0/0x12c el0t_64_sync+0x158/0x15c [E] complete(&vfork:0): [<ffffffc00801f49c>] mm_release+0x7c/0x90 stacktrace: dept_event+0xe0/0x100 complete+0x48/0x98 mm_release+0x7c/0x90 exit_mm_release+0xc/0x14 do_exit+0x1b4/0x81c do_group_exit+0x30/0x9c __wake_up_parent+0x0/0x24 invoke_syscall.constprop.0+0x78/0xc4 do_el0_svc+0x98/0xd0 el0_svc+0x44/0xe4 el0t_64_sync_handler+0xb0/0x12c el0t_64_sync+0x158/0x15c --------------------------------------------------- information that might be helpful --------------------------------------------------- CPU: 6 PID: 229 Comm: start-stop-daem Tainted: G W 5.17.0-rc1+ #3 Hardware name: linux,dummy-virt (DT) Call trace: dump_backtrace.part.0+0x9c/0xc4 show_stack+0x14/0x28 dump_stack_lvl+0x9c/0xcc dump_stack+0x14/0x2c print_circle+0x2d4/0x438 cb_check_dl+0x44/0x70 bfs+0x60/0x168 add_dep+0x88/0x11c do_event.constprop.0+0x19c/0x2c0 dept_event+0xe0/0x100 complete+0x48/0x98 mm_release+0x7c/0x90 exit_mm_release+0xc/0x14 do_exit+0x1b4/0x81c do_group_exit+0x30/0x9c __wake_up_parent+0x0/0x24 invoke_syscall.constprop.0+0x78/0xc4 do_el0_svc+0x98/0xd0 el0_svc+0x44/0xe4 el0t_64_sync_handler+0xb0/0x12c el0t_64_sync+0x158/0x15c =================================================== DEPT: Circular dependency has been detected. 5.17.0-rc1+ #3 Tainted: G W --------------------------------------------------- summary --------------------------------------------------- *** AA DEADLOCK *** context A [S] (unknown)(&try_completion:0) [W] wait_for_completion_timeout(&try_completion:0) [E] complete(&try_completion:0) [S]: start of the event context [W]: the wait blocked [E]: the event not reachable --------------------------------------------------- context A's detail --------------------------------------------------- context A [S] (unknown)(&try_completion:0) [W] wait_for_completion_timeout(&try_completion:0) [E] complete(&try_completion:0) [S] (unknown)(&try_completion:0): (N/A) [W] wait_for_completion_timeout(&try_completion:0): [<ffffffc008166bf4>] kunit_try_catch_run+0xb4/0x160 stacktrace: dept_wait+0x74/0x88 wait_for_completion_timeout+0x64/0xa0 kunit_try_catch_run+0xb4/0x160 kunit_test_try_catch_successful_try_no_catch+0x3c/0x98 kunit_try_run_case+0x9c/0xa0 kunit_generic_run_threadfn_adapter+0x1c/0x28 kthread+0xd4/0xe4 ret_from_fork+0x10/0x20 [E] complete(&try_completion:0): [<ffffffc00803dce4>] kthread_complete_and_exit+0x18/0x20 stacktrace: dept_event+0xe0/0x100 complete+0x48/0x98 kthread_complete_and_exit+0x18/0x20 kunit_try_catch_throw+0x0/0x1c kthread+0xd4/0xe4 ret_from_fork+0x10/0x20 --------------------------------------------------- information that might be helpful --------------------------------------------------- CPU: 15 PID: 132 Comm: kunit_try_catch Tainted: G W 5.17.0-rc1+ #3 Hardware name: linux,dummy-virt (DT) Call trace: dump_backtrace.part.0+0x9c/0xc4 show_stack+0x14/0x28 dump_stack_lvl+0x9c/0xcc dump_stack+0x14/0x2c print_circle+0x2d4/0x438 cb_check_dl+0x44/0x70 bfs+0x60/0x168 add_dep+0x88/0x11c do_event.constprop.0+0x19c/0x2c0 dept_event+0xe0/0x100 complete+0x48/0x98 kthread_complete_and_exit+0x18/0x20 kunit_try_catch_throw+0x0/0x1c kthread+0xd4/0xe4 ret_from_fork+0x10/0x20 > 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: [...] > -- > 1.9.1 > -- Thank you, You are awesome! Hyeonggon :-)
