Return-Path: Received: from zeniv.linux.org.uk ([195.92.253.2]:50282 "EHLO ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751126AbcFCF47 (ORCPT ); Fri, 3 Jun 2016 01:56:59 -0400 Date: Fri, 3 Jun 2016 06:56:55 +0100 From: Al Viro To: Oleg Drokin Cc: "J. Bruce Fields" , linux-nfs@vger.kernel.org, " Mailing List" , "" Subject: Re: NFS/d_splice_alias breakage Message-ID: <20160603055655.GQ14480@ZenIV.linux.org.uk> References: <20160603033750.GL14480@ZenIV.linux.org.uk> <0C971585-6BFC-4665-832B-9B262F733BFC@linuxhacker.ru> <20160603042648.GN14480@ZenIV.linux.org.uk> <51139F5D-8CC8-4448-B3AB-5EF1B67E2D6C@linuxhacker.ru> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <51139F5D-8CC8-4448-B3AB-5EF1B67E2D6C@linuxhacker.ru> Sender: linux-nfs-owner@vger.kernel.org List-ID: On Fri, Jun 03, 2016 at 12:58:10AM -0400, Oleg Drokin wrote: > This one cures the insta-crash I was having, and I see no other ill-effects so far. OK... I can take it through vfs.git, but I think it'd be better off in NFS tree. Is everyone OK with something like the following? make nfs_atomic_open() call d_drop() on all ->open_context() errors. In "NFSv4: Move dentry instantiation into the NFSv4-specific atomic open code" unconditional d_drop() after the ->open_context() had been removed. It had been correct for success cases (there ->open_context() itself had been doing dcache manipulations), but not for error ones. Only one of those (ENOENT) got a compensatory d_drop() added in that commit, but in fact it should've been done for all errors. As it is, the case of O_CREAT non-exclusive open on a hashed negative dentry racing with e.g. symlink creation from another client ended up with ->open_context() getting an error and proceeding to call nfs_lookup(). On a hashed dentry, which would've instantly triggered BUG_ON() in d_materialise_unique() (or, these days, its equivalent in d_splice_alias()). Cc: stable@vger.kernel.org # v3.10+ Tested-by: Oleg Drokin Signed-off-by: Al Viro --- diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c index aaf7bd0..6e3a6f4 100644 --- a/fs/nfs/dir.c +++ b/fs/nfs/dir.c @@ -1536,9 +1536,9 @@ int nfs_atomic_open(struct inode *dir, struct dentry *dentry, err = PTR_ERR(inode); trace_nfs_atomic_open_exit(dir, ctx, open_flags, err); put_nfs_open_context(ctx); + d_drop(dentry); switch (err) { case -ENOENT: - d_drop(dentry); d_add(dentry, NULL); nfs_set_verifier(dentry, nfs_save_change_attribute(dir)); break;