Messages in this thread | | | Date | Wed, 3 Apr 2019 13:44:10 +0100 | From | Will Deacon <> | Subject | Re: [PATCH] locking/lockdep: Zap lock classes even with lock debugging disabled |
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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 <tglx@linutronix.de> > Cc: Will Deacon <will.deacon@arm.com> > Cc: Waiman Long <longman@redhat.com> > Cc: shenghui <shhuiw@foxmail.com> > Reported-by: shenghui <shhuiw@foxmail.com> > Fixes: a0b0fd53e1e6 ("locking/lockdep: Free lock classes that are no longer in use") # v5.1-rc1. > Signed-off-by: Bart Van Assche <bvanassche@acm.org> > --- > 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
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