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Date: Thu, 5 Sep 2013 16:26:51 +0200 From: Miklos Szeredi <miklos@...redi.hu> To: Al Viro <viro@...IV.linux.org.uk> Cc: Linux-Fsdevel <linux-fsdevel@...r.kernel.org>, Kernel Mailing List <linux-kernel@...r.kernel.org>, "mszeredi@...e.cz" <mszeredi@...e.cz>, David Howells <dhowells@...hat.com>, Steven Whitehouse <swhiteho@...hat.com>, Trond Myklebust <Trond.Myklebust@...app.com>, Greg Kroah-Hartman <gregkh@...uxfoundation.org> Subject: Re: [PATCH 04/11] vfs: check unlinked ancestors before mount On Thu, Sep 05, 2013 at 02:23:25PM +0100, Al Viro wrote: > On Thu, Sep 05, 2013 at 02:39:11PM +0200, Miklos Szeredi wrote: > > +static bool __has_unlinked_ancestor(struct dentry *dentry) > > +{ > > + struct dentry *this; > > + > > + for (this = dentry; !IS_ROOT(this); this = this->d_parent) { > > + int is_unhashed; > > + > > + /* Need exclusion wrt. check_submounts_and_drop() */ > > + spin_lock(&this->d_lock); > > + is_unhashed = d_unhashed(this); > > + spin_unlock(&this->d_lock); > > + > > + if (is_unhashed) > > + return true; > > + } > > + return false; > > +} > > I still don't get it; why do you need to bother with early setting of > DCACHE_MOUNTED? > > You are grabbing rename_lock for write in d_set_mounted(). What kind of races > with check for submounts are you worried about? d_walk() will rescan > everything if something grabs rename_lock for write while it had been running, > so just fold the "have nothing in d_subdir" case of check_submounts_and_drop() > into d_walk() and be done with that... What's the problem with such > variant? AFAICS, all you need to care about is d_set_mounted() not getting > between the scan for submounts and actual __d_drop() and your "finish" > callback is called only after d_walk() having grabbed d_lock *and* rechecked > rename_lock. Okay, I get it. So this should work: int d_set_mounted(struct dentry *dentry) { int ret = -ENOENT; write_seqlock(&rename_lock); if (!__has_unlinked_ancestor(dentry->d_parent)) { spin_lock(&dentry->d_lock); if (!d_unlinked(dentry)) { dentry->d_flags |= DCACHE_MOUNTED; ret = 0; } spin_unlock(&dentry->d_lock); } write_sequnlock(&rename_lock); return ret; } The __has_unlinked_ancestor(dentry->d_parent) will work if dentry is a root, but maybe it would be clearer to add that IS_ROOT explicitly? Thanks, Miklos -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.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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