On 07/20/2017 11:08 AM, Miklos Szeredi wrote:
> On Thu, Jul 20, 2017 at 4:21 PM, Waiman Long <longman@xxxxxxxxxx> wrote:
>> On 07/20/2017 03:20 AM, Miklos Szeredi wrote:
>>> On Wed, Jul 19, 2017 at 10:42 PM, Waiman Long <longman@xxxxxxxxxx> wrote:
>>>>>> @@ -603,7 +698,13 @@ static struct dentry *dentry_kill(struct dentry *dentry)
>>>>>>
>>>>>> if (!IS_ROOT(dentry)) {
>>>>>> parent = dentry->d_parent;
>>>>>> - if (unlikely(!spin_trylock(&parent->d_lock))) {
>>>>>> + /*
>>>>>> + * Force the killing of this negative dentry when
>>>>>> + * DCACHE_KILL_NEGATIVE flag is set.
>>>>>> + */
>>>>>> + if (unlikely(dentry->d_flags & DCACHE_KILL_NEGATIVE)) {
>>>>>> + spin_lock(&parent->d_lock);
>>>>> This looks like d_lock ordering problem (should be parent first, child
>>>>> second). Why is this needed, anyway?
>>>>>
>>>> Yes, that is a bug. I should have used lock_parent() instead.
>>> lock_parent() can release dentry->d_lock, which means it's perfectly
>>> useless for this.
>> As the reference count is kept at 1 in dentry_kill(), the dentry won't
>> go away even if the dentry lock is temporarily released.
> It won't go away, but anything else might happen to it (ref grabbed by
> somebody else, instantiated, etc). Don't see how it's going to be
> better than the existing trylock.
>
> Thanks,
> Miklos
In the unlikely event that the reference count or the d_flags changes,
we can abort the killing.
Cheers,
Longman
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