On Tue, Mar 26, 2019 at 12:59:12PM -0700, Bart Van Assche wrote:
> Commit a0b0fd53e1e6 ("locking/lockdep: Free lock classes that are no longer
> in use") changed the behavior of lockdep_free_key_range() from
> unconditionally zapping lock classes into only zapping lock classes if
> debug_lock == true. Since the new behavior can cause cat /proc/lockdep to
> crash due to a NULL pointer dereference, restore the pre-v5.1 behavior.Can you elaborate on this NULL dereference please, and why this patch fixes it? > Cc: Thomas Gleixner <[email protected]> > Cc: Will Deacon <[email protected]> > Cc: Waiman Long <[email protected]> > Cc: shenghui <[email protected]> > Reported-by: shenghui <[email protected]> > Fixes: a0b0fd53e1e6 ("locking/lockdep: Free lock classes that are no longer > in use") # v5.1-rc1. > Signed-off-by: Bart Van Assche <[email protected]> > --- > kernel/locking/lockdep.c | 23 ++++++----------------- > 1 file changed, 6 insertions(+), 17 deletions(-) > > diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c > index 34cdcbedda49..70480e4f8f5d 100644 > --- a/kernel/locking/lockdep.c > +++ b/kernel/locking/lockdep.c > @@ -4689,8 +4689,7 @@ static void free_zapped_rcu(struct rcu_head *ch) > return; > > raw_local_irq_save(flags); > - if (!graph_lock()) > - goto out_irq; > + arch_spin_lock(&lockdep_lock); This also throws out the recursion counting. Is that ok? Will
