* [PATCH] lockdep: Zap lock classes with debug_locks == false again
@ 2022-03-15 11:25 Cheng Jui Wang
2022-03-15 14:48 ` Waiman Long
0 siblings, 1 reply; 2+ messages in thread
From: Cheng Jui Wang @ 2022-03-15 11:25 UTC (permalink / raw)
To: linux-kernel, linux-arm-kernel, linux-mediatek
Cc: Peter Zijlstra, Ingo Molnar, Will Deacon, Waiman Long,
Boqun Feng, Matthias Brugger, Bart Van Assche, wsd_upstream,
Eason-YH Lin, Kobe-CP Wu, Jeff-cc Hsu, Cheng Jui Wang
If a lock_class_key has been registered but lockdep_unregister_key() is
called with debug_locks == false. The lockdep_unregister_key() will not
unregister the key and just return without error.
Users may assume lockdep_unregister_key() always succeed and free the
lock_class_key even if it is still remained in lockdep structures.
Which lead to following crash when 'cat /proc/lockdep' after
debug_locks == false:
==================================================================
BUG: KASAN: invalid-access in string+0x50/0x10c
Read at addr f2ffff81ac61c880 by ...
Pointer tag: [f2], memory tag: [fb]
...
Call trace:
dump_backtrace.cfi_jt+0x0/0x8
show_stack+0x1c/0x2c
dump_stack_lvl+0xd8/0x16c
print_address_description+0x90/0x2e8
__kasan_report+0x144/0x224
kasan_report+0x50/0xa0
__do_kernel_fault+0xf4/0x2a8
do_bad_area+0x34/0xf8
do_tag_check_fault+0x24/0x38
do_mem_abort+0x68/0x168
el1_abort+0x4c/0x74
el1_sync_handler+0x4c/0x8c
el1_sync+0x8c/0x140
string+0x50/0x10c
vsnprintf+0x468/0x69c
seq_printf+0x8c/0xd8
print_name+0x64/0xf4
l_show+0x1a8/0x278
seq_read_iter+0x3cc/0x5fc
proc_reg_read_iter+0xdc/0x1d4
vfs_read+0x2e0/0x354
ksys_read+0x7c/0xec
__arm64_sys_read+0x20/0x30
el0_svc_common.llvm.8008154191216078041+0xd8/0x20c
do_el0_svc+0x28/0xa0
el0_svc+0x24/0x38
el0_sync_handler+0x88/0xec
el0_sync+0x1b4/0x1c0
...
==================================================================
Allow lockdep_unregister_key to zap lock classes with
debug_locks == false again.
Remove the WARN_ON_ONCE(!found) and only zap lock classes when the key
can be found.
Fixes: 8b39adbee805 ("locking/lockdep: Make lockdep_unregister_key() honor 'debug_locks' again")
Signed-off-by: Cheng Jui Wang <cheng-jui.wang@mediatek.com>
---
kernel/locking/lockdep.c | 13 ++++++-------
1 file changed, 6 insertions(+), 7 deletions(-)
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index f8a0212189ca..90dadecb2577 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -6305,8 +6305,7 @@ void lockdep_unregister_key(struct lock_class_key *key)
return;
raw_local_irq_save(flags);
- if (!graph_lock())
- goto out_irq;
+ lockdep_lock();
pf = get_pending_free();
hlist_for_each_entry_rcu(k, hash_head, hash_entry) {
@@ -6316,11 +6315,11 @@ void lockdep_unregister_key(struct lock_class_key *key)
break;
}
}
- WARN_ON_ONCE(!found);
- __lockdep_free_key_range(pf, key, 1);
- call_rcu_zapped(pf);
- graph_unlock();
-out_irq:
+ if (found) {
+ __lockdep_free_key_range(pf, key, 1);
+ call_rcu_zapped(pf);
+ }
+ lockdep_unlock();
raw_local_irq_restore(flags);
/* Wait until is_dynamic_key() has finished accessing k->hash_entry. */
--
2.18.0
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] lockdep: Zap lock classes with debug_locks == false again
2022-03-15 11:25 [PATCH] lockdep: Zap lock classes with debug_locks == false again Cheng Jui Wang
@ 2022-03-15 14:48 ` Waiman Long
0 siblings, 0 replies; 2+ messages in thread
From: Waiman Long @ 2022-03-15 14:48 UTC (permalink / raw)
To: Cheng Jui Wang, linux-kernel, linux-arm-kernel, linux-mediatek
Cc: Peter Zijlstra, Ingo Molnar, Will Deacon, Boqun Feng,
Matthias Brugger, Bart Van Assche, wsd_upstream, Eason-YH Lin,
Kobe-CP Wu, Jeff-cc Hsu
On 3/15/22 07:25, Cheng Jui Wang wrote:
> If a lock_class_key has been registered but lockdep_unregister_key() is
> called with debug_locks == false. The lockdep_unregister_key() will not
> unregister the key and just return without error.
> Users may assume lockdep_unregister_key() always succeed and free the
> lock_class_key even if it is still remained in lockdep structures.
>
> Which lead to following crash when 'cat /proc/lockdep' after
> debug_locks == false:
>
> ==================================================================
> BUG: KASAN: invalid-access in string+0x50/0x10c
> Read at addr f2ffff81ac61c880 by ...
> Pointer tag: [f2], memory tag: [fb]
> ...
> Call trace:
> dump_backtrace.cfi_jt+0x0/0x8
> show_stack+0x1c/0x2c
> dump_stack_lvl+0xd8/0x16c
> print_address_description+0x90/0x2e8
> __kasan_report+0x144/0x224
> kasan_report+0x50/0xa0
> __do_kernel_fault+0xf4/0x2a8
> do_bad_area+0x34/0xf8
> do_tag_check_fault+0x24/0x38
> do_mem_abort+0x68/0x168
> el1_abort+0x4c/0x74
> el1_sync_handler+0x4c/0x8c
> el1_sync+0x8c/0x140
> string+0x50/0x10c
> vsnprintf+0x468/0x69c
> seq_printf+0x8c/0xd8
> print_name+0x64/0xf4
> l_show+0x1a8/0x278
> seq_read_iter+0x3cc/0x5fc
> proc_reg_read_iter+0xdc/0x1d4
> vfs_read+0x2e0/0x354
> ksys_read+0x7c/0xec
> __arm64_sys_read+0x20/0x30
> el0_svc_common.llvm.8008154191216078041+0xd8/0x20c
> do_el0_svc+0x28/0xa0
> el0_svc+0x24/0x38
> el0_sync_handler+0x88/0xec
> el0_sync+0x1b4/0x1c0
>
> ...
> ==================================================================
>
> Allow lockdep_unregister_key to zap lock classes with
> debug_locks == false again.
> Remove the WARN_ON_ONCE(!found) and only zap lock classes when the key
> can be found.
>
> Fixes: 8b39adbee805 ("locking/lockdep: Make lockdep_unregister_key() honor 'debug_locks' again")
> Signed-off-by: Cheng Jui Wang <cheng-jui.wang@mediatek.com>
> ---
> kernel/locking/lockdep.c | 13 ++++++-------
> 1 file changed, 6 insertions(+), 7 deletions(-)
>
> diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
> index f8a0212189ca..90dadecb2577 100644
> --- a/kernel/locking/lockdep.c
> +++ b/kernel/locking/lockdep.c
> @@ -6305,8 +6305,7 @@ void lockdep_unregister_key(struct lock_class_key *key)
> return;
>
> raw_local_irq_save(flags);
> - if (!graph_lock())
> - goto out_irq;
> + lockdep_lock();
>
> pf = get_pending_free();
> hlist_for_each_entry_rcu(k, hash_head, hash_entry) {
> @@ -6316,11 +6315,11 @@ void lockdep_unregister_key(struct lock_class_key *key)
> break;
> }
> }
> - WARN_ON_ONCE(!found);
> - __lockdep_free_key_range(pf, key, 1);
> - call_rcu_zapped(pf);
> - graph_unlock();
> -out_irq:
> + if (found) {
> + __lockdep_free_key_range(pf, key, 1);
> + call_rcu_zapped(pf);
> + }
> + lockdep_unlock();
> raw_local_irq_restore(flags);
>
> /* Wait until is_dynamic_key() has finished accessing k->hash_entry. */
Thanks for the patch.
However, this is a known problem and had been fixed by commit
61cc4534b655 ("locking/lockdep: Avoid potential access of invalid memory
in lock_class") in the tip tree. It will get merged into v5.18 kernel.
Cheers,
Longman
^ permalink raw reply [flat|nested] 2+ messages in thread
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2022-03-15 14:48 ` Waiman Long
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