On Thu, Mar 03, 2022 at 09:18:13AM +0900, Byungchul Park wrote: > On Wed, Mar 02, 2022 at 04:53:41AM +0000, Hyeonggon Yoo wrote: > > On Wed, Mar 02, 2022 at 04:36:38AM +0000, Hyeonggon Yoo wrote: > > > On Mon, Feb 28, 2022 at 06:56:39PM +0900, Byungchul Park wrote: > > > > I didn't want to bother you so I was planning to send the next spin > > > > after making more progress. However, PATCH v2 reports too many false > > > > positives because Dept tracked the bit_wait_table[] wrong way - I > > > > apologize for that. So I decided to send PATCH v3 first before going > > > > further for those who want to run Dept for now. > > > > > > > > There might still be some false positives but not overwhelming. > > > > > > > > > > Hello Byungchul, I'm running DEPT v3 on my system > > > and I see report below. > > > > > > Looking at the kmemleak code and comment, I think > > > kmemleak tried to avoid lockdep recursive warning > > > but detected by DEPT? > > > > > > > Forgot to include another warning caused by DEPT. > > > > And comment below might be useful for debugging: > > > > in kmemleak.c: > > 43 * Locks and mutexes are acquired/nested in the following order: > > 44 * > > 45 * scan_mutex [-> object->lock] -> kmemleak_lock -> other_object->lock (SINGLE_DEPTH_NESTING) > > 46 * > > 47 * No kmemleak_lock and object->lock nesting is allowed outside scan_mutex > > 48 * regions. > > > > =================================================== > > DEPT: Circular dependency has been detected. > > 5.17.0-rc1+ #1 Tainted: G W > > --------------------------------------------------- > > summary > > --------------------------------------------------- > > *** DEADLOCK *** > > > > context A > > [S] __raw_spin_lock_irqsave(&object->lock:0) > > [W] __raw_spin_lock_irqsave(kmemleak_lock:0) > > [E] spin_unlock(&object->lock:0) > > > > context B > > [S] __raw_spin_lock_irqsave(kmemleak_lock:0) > > [W] _raw_spin_lock_nested(&object->lock:0) > > [E] spin_unlock(kmemleak_lock:0) > > > > [S]: start of the event context > > [W]: the wait blocked > > [E]: the event not reachable > > Hi Hyeonggon, > > Dept also allows the following scenario when an user guarantees that > each lock instance is different from another at a different depth: > > lock A0 with depth > lock A1 with depth + 1 > lock A2 with depth + 2 > lock A3 with depth + 3 > (and so on) > .. > unlock A3 > unlock A2 > unlock A1 > unlock A0 > > However, Dept does not allow the following scenario where another lock > class cuts in the dependency chain: > > lock A0 with depth > lock B > lock A1 with depth + 1 > lock A2 with depth + 2 > lock A3 with depth + 3 > (and so on) > .. > unlock A3 > unlock A2 > unlock A1 > unlock B > unlock A0 > > This scenario is clearly problematic. What do you think is going to > happen with another context running the following? > First of all, I want to say I'm not expert at locking primitives. I may be wrong. > > 45 * scan_mutex [-> object->lock] -> kmemleak_lock -> other_object->lock (SINGLE_DEPTH_NESTING) > > 46 * > > 47 * No kmemleak_lock and object->lock nesting is allowed outside scan_mutex > > 48 * regions. lock order in kmemleak is described above. and DEPT detects two cases as deadlock: 1) object->lock -> other_object->lock 2) object->lock -> kmemleak_lock, kmemleak_lock -> other_object->lock And in kmemleak case, 1) and 2) is not possible because it must hold scan_mutex first. I think the author of kmemleak intended lockdep to treat object->lock and other_object->lock as different class, using raw_spin_lock_nested(). Am I missing something? Thanks. > lock A1 with depth > lock B > lock A2 with depth + 1 > lock A3 with depth + 2 > (and so on) > .. > unlock A3 > unlock A2 > unlock B > unlock A1 > > It's a deadlock. That's why Dept reports this case as a problem. Or am I > missing something? > > Thanks, > Byungchul > > > --------------------------------------------------- > > context A's detail > > --------------------------------------------------- > > context A > > [S] __raw_spin_lock_irqsave(&object->lock:0) > > [W] __raw_spin_lock_irqsave(kmemleak_lock:0) > > [E] spin_unlock(&object->lock:0) > > > > [S] __raw_spin_lock_irqsave(&object->lock:0): > > [<ffffffc00810302c>] scan_gray_list+0x84/0x13c > > stacktrace: > > dept_ecxt_enter+0x88/0xf4 > > _raw_spin_lock_irqsave+0xf0/0x1c4 > > scan_gray_list+0x84/0x13c > > kmemleak_scan+0x2d8/0x54c > > kmemleak_scan_thread+0xac/0xd4 > > kthread+0xd4/0xe4 > > ret_from_fork+0x10/0x20 > > > > [W] __raw_spin_lock_irqsave(kmemleak_lock:0): > > [<ffffffc008102ebc>] scan_block+0x3c/0x128 > > stacktrace: > > __dept_wait+0x8c/0xa4 > > dept_wait+0x6c/0x88 > > _raw_spin_lock_irqsave+0xb8/0x1c4 > > scan_block+0x3c/0x128 > > scan_gray_list+0xc4/0x13c > > kmemleak_scan+0x2d8/0x54c > > kmemleak_scan_thread+0xac/0xd4 > > kthread+0xd4/0xe4 > > ret_from_fork+0x10/0x20 > > > > [E] spin_unlock(&object->lock:0): > > [<ffffffc008102ee0>] scan_block+0x60/0x128 > > > > --------------------------------------------------- > > context B's detail > > --------------------------------------------------- > > context B > > [S] __raw_spin_lock_irqsave(kmemleak_lock:0) > > [W] _raw_spin_lock_nested(&object->lock:0) > > [E] spin_unlock(kmemleak_lock:0) > > > > [S] __raw_spin_lock_irqsave(kmemleak_lock:0): > > [<ffffffc008102ebc>] scan_block+0x3c/0x128 > > stacktrace: > > dept_ecxt_enter+0x88/0xf4 > > _raw_spin_lock_irqsave+0xf0/0x1c4 > > scan_block+0x3c/0x128 > > kmemleak_scan+0x19c/0x54c > > kmemleak_scan_thread+0xac/0xd4 > > kthread+0xd4/0xe4 > > ret_from_fork+0x10/0x20 > > > > [W] _raw_spin_lock_nested(&object->lock:0): > > [<ffffffc008102f34>] scan_block+0xb4/0x128 > > stacktrace: > > dept_wait+0x74/0x88 > > _raw_spin_lock_nested+0xa8/0x1b0 > > scan_block+0xb4/0x128 > > kmemleak_scan+0x19c/0x54c > > kmemleak_scan_thread+0xac/0xd4 > > kthread+0xd4/0xe4 > > ret_from_fork+0x10/0x20 > > [E] spin_unlock(kmemleak_lock:0): > > [<ffffffc008102ee0>] scan_block+0x60/0x128 > > stacktrace: > > dept_event+0x7c/0xfc > > _raw_spin_unlock_irqrestore+0x8c/0x120 > > scan_block+0x60/0x128 > > kmemleak_scan+0x19c/0x54c > > kmemleak_scan_thread+0xac/0xd4 > > kthread+0xd4/0xe4 > > ret_from_fork+0x10/0x20 > > --------------------------------------------------- > > information that might be helpful > > --------------------------------------------------- > > CPU: 1 PID: 38 Comm: kmemleak Tainted: G W 5.17.0-rc1+ #1 > > 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+0x6c/0x70 > > bfs+0xc0/0x168 > > add_dep+0x88/0x11c > > add_wait+0x2d0/0x2dc > > __dept_wait+0x8c/0xa4 > > dept_wait+0x6c/0x88 > > _raw_spin_lock_irqsave+0xb8/0x1c4 > > scan_block+0x3c/0x128 > > scan_gray_list+0xc4/0x13c > > kmemleak_scan+0x2d8/0x54c > > kmemleak_scan_thread+0xac/0xd4 > > kthread+0xd4/0xe4 > > ret_from_fork+0x10/0x20 > > > > > =================================================== > > > DEPT: Circular dependency has been detected. > > > 5.17.0-rc1+ #1 Tainted: G W > > > --------------------------------------------------- > > > summary > > > --------------------------------------------------- > > > *** AA DEADLOCK *** > > > > > > context A > > > [S] __raw_spin_lock_irqsave(&object->lock:0) > > > [W] _raw_spin_lock_nested(&object->lock:0) > > > [E] spin_unlock(&object->lock:0) > > > > > > [S]: start of the event context > > > [W]: the wait blocked > > > [E]: the event not reachable > > > --------------------------------------------------- > > > context A's detail > > > --------------------------------------------------- > > > context A > > > [S] __raw_spin_lock_irqsave(&object->lock:0) > > > [W] _raw_spin_lock_nested(&object->lock:0) > > > [E] spin_unlock(&object->lock:0) > > > > > > [S] __raw_spin_lock_irqsave(&object->lock:0): > > > [<ffffffc00810302c>] scan_gray_list+0x84/0x13c > > > stacktrace: > > > dept_ecxt_enter+0x88/0xf4 > > > _raw_spin_lock_irqsave+0xf0/0x1c4 > > > scan_gray_list+0x84/0x13c > > > kmemleak_scan+0x2d8/0x54c > > > kmemleak_scan_thread+0xac/0xd4 > > > kthread+0xd4/0xe4 > > > ret_from_fork+0x10/0x20 > > > > > > [E] spin_unlock(&object->lock:0): > > > [<ffffffc008102ee0>] scan_block+0x60/0x128 > > > --------------------------------------------------- > > > information that might be helpful > > > --------------------------------------------------- > > > CPU: 1 PID: 38 Comm: kmemleak Tainted: G W 5.17.0-rc1+ #1 > > > 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 > > > add_wait+0x2d0/0x2dc > > > __dept_wait+0x8c/0xa4 > > > dept_wait+0x6c/0x88 > > > _raw_spin_lock_nested+0xa8/0x1b0 > > > scan_block+0xb4/0x128 > > > scan_gray_list+0xc4/0x13c > > > kmemleak_scan+0x2d8/0x54c > > > kmemleak_scan_thread+0xac/0xd4 > > > kthread+0xd4/0xe4 > > > ret_from_fork+0x10/0x20 > > > > > [...] > > > > -- > > Thank you, You are awesome! > > Hyeonggon :-) -- Thank you, You are awesome! Hyeonggon :-)
