lockdep: Correct lock_classes index mapping

stable inclusion
from stable-v5.10.102
commit 6062d1267ff3e5570165c974bb0dc2120c9d363c
bugzilla: https://gitee.com/openeuler/kernel/issues/I567K6

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6062d1267ff3e5570165c974bb0dc2120c9d363c

--------------------------------

commit 28df029d upstream.

A kernel exception was hit when trying to dump /proc/lockdep_chains after
lockdep report "BUG: MAX_LOCKDEP_CHAIN_HLOCKS too low!":

Unable to handle kernel paging request at virtual address 00054005450e05c3
...
00054005450e05c3] address between user and kernel address ranges
...
pc : [0xffffffece769b3a8] string+0x50/0x10c
lr : [0xffffffece769ac88] vsnprintf+0x468/0x69c
...
 Call trace:
  string+0x50/0x10c
  vsnprintf+0x468/0x69c
  seq_printf+0x8c/0xd8
  print_name+0x64/0xf4
  lc_show+0xb8/0x128
  seq_read_iter+0x3cc/0x5fc
  proc_reg_read_iter+0xdc/0x1d4

The cause of the problem is the function lock_chain_get_class() will
shift lock_classes index by 1, but the index don't need to be shifted
anymore since commit 01bb6f0a ("locking/lockdep: Change the range
of class_idx in held_lock struct") already change the index to start
from 0.

The lock_classes[-1] located at chain_hlocks array. When printing
lock_classes[-1] after the chain_hlocks entries are modified, the
exception happened.

The output of lockdep_chains are incorrect due to this problem too.

Fixes: f611e8cf ("lockdep: Take read/write status in consideration when generate chainkey")
Signed-off-by: NCheng Jui Wang <cheng-jui.wang@mediatek.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: NBoqun Feng <boqun.feng@gmail.com>
Link: https://lore.kernel.org/r/20220210105011.21712-1-cheng-jui.wang@mediatek.comSigned-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NYu Liao <liaoyu15@huawei.com>
Reviewed-by: NWei Li <liwei391@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

kernel/locking/lockdep.c

@@ -3387,7 +3387,7 @@ struct lock_class *lock_chain_get_class(struct lock_chain *chain, int i)
 	u16 chain_hlock = chain_hlocks[chain->base + i];
 	unsigned int class_idx = chain_hlock_class_idx(chain_hlock);
 
-	return lock_classes + class_idx - 1;
+	return lock_classes + class_idx;
 }
 
 /*
@@ -3455,7 +3455,7 @@ static void print_chain_keys_chain(struct lock_chain *chain)
 		hlock_id = chain_hlocks[chain->base + i];
 		chain_key = print_chain_key_iteration(hlock_id, chain_key);
 
-		print_lock_name(lock_classes + chain_hlock_class_idx(hlock_id) - 1);
+		print_lock_name(lock_classes + chain_hlock_class_idx(hlock_id));
 		printk("\n");
 	}
 }