On Thursday March 9, [email protected] wrote:
> Andrew,
>
> Acked-By: Kirill Korotaev <[email protected]>
I'm afraid that I'm not convinced.
> > +static int wait_on_prunes(struct super_block *sb)
> > +{
> > + DEFINE_WAIT(wait);
> > + int prunes_remaining = 0;
> > +
> > +#ifdef DCACHE_DEBUG
> > + printk(KERN_DEBUG "%s: waiting for %d prunes\n", __FUNCTION__,
> > + sb->s_prunes);
> > +#endif
> > +
> > + spin_lock(&dcache_lock);
> > + for (;;) {
> > + prepare_to_wait(&sb->s_wait_prunes, &wait,
> > + TASK_UNINTERRUPTIBLE);
> > + if (!sb->s_prunes)
> > + break;
> > + spin_unlock(&dcache_lock);
> > + schedule();
> > + prunes_remaining = 1;
> > + spin_lock(&dcache_lock);
> > + }
> > + spin_unlock(&dcache_lock);
> > + finish_wait(&sb->s_wait_prunes, &wait);
> > + return prunes_remaining;
> > +}
I don't think that a return value from wait_on_prunes is meaningful.
All it tells us is whether a prune_one_dentry finished before or after
wait_on_prunes takes the spin_lock. This isn't very useful
information as it has no significance to upper levels.
So:
> > + do {
> > + shrink_dcache_parent(root);
> > + } while(wait_on_prunes(sb));
> > +
Suppose shrink_dcache_parent misses on dentry because the inode was being
iput. This iput completes immediately that
shrink_dcache_parent completes. It decrements ->s_prunes and when
wait_on_prunes takes dcache_lock, ->s_prunes is zero so the loop
terminates, and the remaining dentries - the parents of the dentry
what was undergoing iput - don't get put.
I really think that we need to stop prune_one_dentry from being called
on dentries for a filesystem that is being unmounted. With that code
currently in -git, that means passing a 'struct super_block *' into
prune_dcache so that it ignores any filesystem with ->s_root==NULL
unless that filesystem is the filesystem that was passed.
NeilBrown
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