On Mon, Apr 08, 2013 at 05:14:44PM +0400, Glauber Costa wrote:
> On 03/29/2013 01:13 PM, Glauber Costa wrote:
> > + if (dentry->d_flags & DCACHE_REFERENCED) {
> > + dentry->d_flags &= ~DCACHE_REFERENCED;
> > + spin_unlock(&dentry->d_lock);
> > +
> > + /*
> > + * XXX: this list move should be be done under d_lock. Need to
> > + * determine if it is safe just to do it under the lru lock.
> > + */
> > + return 1;
> > + }
>
> I've carefully audited the list manipulations in dcache and determined
> this is safe. I've replaced the fixme string for the following text. Let
> me know if you believe this is not right.
....
> diff --git a/fs/dcache.c b/fs/dcache.c
> index a2fc76e..8e166a4 100644
> --- a/fs/dcache.c
> +++ b/fs/dcache.c
> @@ -855,8 +855,23 @@ dentry_lru_isolate(struct list_head *item, spinlock_t *lru_lock, void *arg)
> spin_unlock(&dentry->d_lock);
>
> /*
> - * XXX: this list move should be be done under d_lock. Need to
> - * determine if it is safe just to do it under the lru lock.
> + * The list move itself will be made by the common LRU code. At
> + * this point, we've dropped the dentry->d_lock but keep the
> + * lru lock. This is safe to do, since every list movement is
> + * protected by the lru lock even if both locks are held.
> + *
> + * This is guaranteed by the fact that all LRU management
> + * functions are intermediated by the LRU API calls like
> + * list_lru_add and list_lru_del. List movement in this file
> + * only ever occur through this functions or through callbacks
> + * like this one, that are called from the LRU API.
> + *
> + * The only exceptions to this are functions like
> + * shrink_dentry_list, and code that first checks for the
> + * DCACHE_SHRINK_LIST flag. Those are guaranteed to be
> + * operating only with stack provided lists after they are
> + * properly isolated from the main list. It is thus, always a
> + * local access.
> */
> return LRU_ROTATE;
It looks correct - I just never got around to doing the audit to
determine it was. Thanks!
Cheers,
Dave.
--
Dave Chinner
david@xxxxxxxxxxxxx
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