Messages in this thread | | | From | Neil Brown <> | Date | Fri, 10 Mar 2006 16:09:54 +1100 | Subject | Re: [PATCH] Fix shrink_dcache_parent() against shrink_dcache_memory() race (3rd updated patch)] |
| |
On Thursday March 9, dev@openvz.org wrote: > Andrew, > > Acked-By: Kirill Korotaev <dev@openvz.org>
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 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |