Messages in this thread | | | Date | Tue, 15 Mar 2022 10:48:25 -0400 | Subject | Re: [PATCH] lockdep: Zap lock classes with debug_locks == false again | From | Waiman Long <> |
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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
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