Re: [PATCH 1/2] vfs: make real_lookup do dentry revalidation with i_mutex held

[Ian Kent <raven@themaw.net>]

Ian Kent wrote:
> Ian Kent wrote:
>> Sage Weil wrote:
>>> Would it be possible to avoid the upcall in revalidate, and instead fail 
>>> and let the subsequent lookup path do it?  (I'm guessing the upcall 
>>> doesn't happen for _every_ revalidate?)
> 
> snip ...
> 
>> It was more than three years ago when I tried to make everything go
>> through lookup so my memory is pretty unclear now. In the end I think
>> there was one case in real_lookup() where the lookup was skipped,
>> revalidate was called and failed but lookup wasn't then called again and
>> I got an incorrect failure. AFAICR all other code paths that hold the
>> mutex over lookup and revalidate perform the revalidate first and then
>> the lookup if that fails, which avoids this case.
> 
> I've managed to locate the work that I did on this (on an old machine I
> left as it was for posterity).
> 
> I haven't had a chance to look at what I did closely and a lot has
> changed in autofs4 since. The one thing that I'm fairly sure I would
> need to be able to make this work is the order of the calls in
> real_lookup() to be revalidate then lookup. Would that work for
> real_lookup() given that we hold the mutex now?

DOH, which both patches together end up doing.

> 
> In fact this might be an opportunity for me to clean up my sloppy
> DCACHE_AUTOFS_PENDING handling by moving it all under the inode mutex.

Unfortunately not, I still need to use this in the follow_link() method
without the lock.

Ian