lockdep: Correct lock_classes index mapping

BugLink: https://bugs.launchpad.net/bugs/1963890
commit 28df029d53a2fd80c1b8674d47895648ad26dcfb 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 01bb6f0af992 ("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: f611e8cf98ec ("lockdep: Take read/write status in consideration when generate chainkey")
Signed-off-by: Cheng Jui Wang <cheng-jui.wang@mediatek.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Boqun Feng <boqun.feng@gmail.com>
Link: https://lore.kernel.org/r/20220210105011.21712-1-cheng-jui.wang@mediatek.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 0627584f7872ad32961b071815e3f21e225f23ca..7d5b4e78bb5c7ebf80a1302d35b7c7021bdc4f29 100644 (file)
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -3452,7 +3452,7 @@ 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;
 }
 
 /*
@@ -3520,7 +3520,7 @@ 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");
        }
 }