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    Subject[PATCH 4.19 41/45] locking/lockdep: Add debug_locks check in __lock_downgrade()
    Date
    4.19-stable review patch.  If anyone has any objections, please let me know.

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

    From: Waiman Long <longman@redhat.com>

    commit 71492580571467fb7177aade19c18ce7486267f5 upstream.

    Tetsuo Handa had reported he saw an incorrect "downgrading a read lock"
    warning right after a previous lockdep warning. It is likely that the
    previous warning turned off lock debugging causing the lockdep to have
    inconsistency states leading to the lock downgrade warning.

    Fix that by add a check for debug_locks at the beginning of
    __lock_downgrade().

    Debugged-by: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
    Reported-by: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
    Reported-by: syzbot+53383ae265fb161ef488@syzkaller.appspotmail.com
    Signed-off-by: Waiman Long <longman@redhat.com>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: Will Deacon <will.deacon@arm.com>
    Link: https://lkml.kernel.org/r/1547093005-26085-1-git-send-email-longman@redhat.com
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    kernel/locking/lockdep.c | 3 +++
    1 file changed, 3 insertions(+)

    --- a/kernel/locking/lockdep.c
    +++ b/kernel/locking/lockdep.c
    @@ -3567,6 +3567,9 @@ __lock_set_class(struct lockdep_map *loc
    unsigned int depth;
    int i;

    + if (unlikely(!debug_locks))
    + return 0;
    +
    depth = curr->lockdep_depth;
    /*
    * This function is about (re)setting the class of a held lock,

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