Messages in this thread | | | Subject | Re: [PATCH 1/2] VFS: Make d_materialise_unique() enforce directory uniqueness | From | Trond Myklebust <> | Date | Fri, 20 Oct 2006 00:54:18 -0400 |
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On Thu, 2006-10-19 at 21:40 -0700, Andrew Morton wrote: > On Thu, 19 Oct 2006 17:03:58 -0400 > Trond Myklebust <Trond.Myklebust@netapp.com> wrote: > > > +static struct dentry *__d_unalias(struct dentry *dentry, struct dentry *alias) > > +{ > > + struct mutex *m1 = NULL, *m2 = NULL; > > + struct dentry *ret; > > + > > + /* If alias and dentry share a parent, then no extra locks required */ > > + if (alias->d_parent == dentry->d_parent) > > + goto out_unalias; > > + > > + /* Check for loops */ > > + ret = ERR_PTR(-ELOOP); > > + if (d_isparent(alias, dentry)) > > + goto out_err; > > + > > + /* See lock_rename() */ > > + ret = ERR_PTR(-EBUSY); > > + if (!mutex_trylock(&dentry->d_sb->s_vfs_rename_mutex)) > > + goto out_err; > > + m1 = &dentry->d_sb->s_vfs_rename_mutex; > > + if (!mutex_trylock(&alias->d_parent->d_inode->i_mutex)) > > + goto out_err; > > + m2 = &alias->d_parent->d_inode->i_mutex; > > +out_unalias: > > + d_move_locked(alias, dentry); > > + ret = alias; > > +out_err: > > + spin_unlock(&dcache_lock); > > + if (m2) > > + mutex_unlock(m2); > > + if (m1) > > + mutex_unlock(m1); > > + return ret; > > +} > > The locking in there is, of course, gruesome. There is no way in which it > can be made reliable?
The generic lookup() code will grab the dir->i_mutex for the parent directory before we get anywhere near __d_alias(). That pretty much limits us to using mutex_trylock() since otherwise we break the nesting rules for lock_rename(), and I can't see that we can release the problematic dir->i_mutex without causing worse races.
Cheers, Trond - 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/
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