From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.0 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,T_DKIMWL_WL_HIGH,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 76716C282DD for ; Thu, 23 May 2019 19:21:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 43F922184E for ; Thu, 23 May 2019 19:21:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1558639309; bh=HDV0V+3q18n4NciByt+kY8RlDLe68ZzcqfT7OotFAPw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=pVyhwkbtiePVlLJaki3yWNp3UxQdBR4jo8oO6eW+k9sjNlBLgt0sZ/fmOaTQgKdXD TDu29dnDfS+L+YYuEuAFE0tvezQj1lDA9o43WhpVYmOt907NDdIYXjjtWrco72vhqP OnfqHL1OAV3lfmrHXujUQLnGoQJ2H0yawOzX2YlM= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390347AbfEWTVr (ORCPT ); Thu, 23 May 2019 15:21:47 -0400 Received: from mail.kernel.org ([198.145.29.99]:59166 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2390323AbfEWTVm (ORCPT ); Thu, 23 May 2019 15:21:42 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 3496C20863; Thu, 23 May 2019 19:21:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1558639301; bh=HDV0V+3q18n4NciByt+kY8RlDLe68ZzcqfT7OotFAPw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=LwyW313Vdw60mLYQiglxriBGrRUl0IHbhvkuY0wfx893ZY1RbABVFTv9haBNAaaIS NOuuJw1bbpXegIE9sD9hV8AElirB0NwIfsZwwsGLmA6thGfWD9FWylHa9BAHSKrVi6 LYhbZG2IVnBNJarJHN5QzOeBn0pGphyT7rxjGLnw= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Al Viro Subject: [PATCH 5.0 037/139] dcache: sort the freeing-without-RCU-delay mess for good. Date: Thu, 23 May 2019 21:05:25 +0200 Message-Id: <20190523181725.598384602@linuxfoundation.org> X-Mailer: git-send-email 2.21.0 In-Reply-To: <20190523181720.120897565@linuxfoundation.org> References: <20190523181720.120897565@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Al Viro commit 5467a68cbf6884c9a9d91e2a89140afb1839c835 upstream. For lockless accesses to dentries we don't have pinned we rely (among other things) upon having an RCU delay between dropping the last reference and actually freeing the memory. On the other hand, for things like pipes and sockets we neither do that kind of lockless access, nor want to deal with the overhead of an RCU delay every time a socket gets closed. So delay was made optional - setting DCACHE_RCUACCESS in ->d_flags made sure it would happen. We tried to avoid setting it unless we knew we need it. Unfortunately, that had led to recurring class of bugs, in which we missed the need to set it. We only really need it for dentries that are created by d_alloc_pseudo(), so let's not bother with trying to be smart - just make having an RCU delay the default. The ones that do *not* get it set the replacement flag (DCACHE_NORCU) and we'd better use that sparingly. d_alloc_pseudo() is the only such user right now. FWIW, the race that finally prompted that switch had been between __lock_parent() of immediate subdirectory of what's currently the root of a disconnected tree (e.g. from open-by-handle in progress) racing with d_splice_alias() elsewhere picking another alias for the same inode, either on outright corrupted fs image, or (in case of open-by-handle on NFS) that subdirectory having been just moved on server. It's not easy to hit, so the sky is not falling, but that's not the first race on similar missed cases and the logics for settinf DCACHE_RCUACCESS has gotten ridiculously convoluted. Cc: stable@vger.kernel.org Signed-off-by: Al Viro Signed-off-by: Greg Kroah-Hartman --- Documentation/filesystems/porting | 5 +++++ fs/dcache.c | 24 +++++++++++++----------- fs/nsfs.c | 3 +-- include/linux/dcache.h | 2 +- 4 files changed, 20 insertions(+), 14 deletions(-) --- a/Documentation/filesystems/porting +++ b/Documentation/filesystems/porting @@ -638,3 +638,8 @@ in your dentry operations instead. inode to d_splice_alias() will also do the right thing (equivalent of d_add(dentry, NULL); return NULL;), so that kind of special cases also doesn't need a separate treatment. +-- +[mandatory] + DCACHE_RCUACCESS is gone; having an RCU delay on dentry freeing is the + default. DCACHE_NORCU opts out, and only d_alloc_pseudo() has any + business doing so. --- a/fs/dcache.c +++ b/fs/dcache.c @@ -344,7 +344,7 @@ static void dentry_free(struct dentry *d } } /* if dentry was never visible to RCU, immediate free is OK */ - if (!(dentry->d_flags & DCACHE_RCUACCESS)) + if (dentry->d_flags & DCACHE_NORCU) __d_free(&dentry->d_u.d_rcu); else call_rcu(&dentry->d_u.d_rcu, __d_free); @@ -1701,7 +1701,6 @@ struct dentry *d_alloc(struct dentry * p struct dentry *dentry = __d_alloc(parent->d_sb, name); if (!dentry) return NULL; - dentry->d_flags |= DCACHE_RCUACCESS; spin_lock(&parent->d_lock); /* * don't need child lock because it is not subject @@ -1726,7 +1725,7 @@ struct dentry *d_alloc_cursor(struct den { struct dentry *dentry = d_alloc_anon(parent->d_sb); if (dentry) { - dentry->d_flags |= DCACHE_RCUACCESS | DCACHE_DENTRY_CURSOR; + dentry->d_flags |= DCACHE_DENTRY_CURSOR; dentry->d_parent = dget(parent); } return dentry; @@ -1739,10 +1738,17 @@ struct dentry *d_alloc_cursor(struct den * * For a filesystem that just pins its dentries in memory and never * performs lookups at all, return an unhashed IS_ROOT dentry. + * This is used for pipes, sockets et.al. - the stuff that should + * never be anyone's children or parents. Unlike all other + * dentries, these will not have RCU delay between dropping the + * last reference and freeing them. */ struct dentry *d_alloc_pseudo(struct super_block *sb, const struct qstr *name) { - return __d_alloc(sb, name); + struct dentry *dentry = __d_alloc(sb, name); + if (likely(dentry)) + dentry->d_flags |= DCACHE_NORCU; + return dentry; } EXPORT_SYMBOL(d_alloc_pseudo); @@ -1911,12 +1917,10 @@ struct dentry *d_make_root(struct inode if (root_inode) { res = d_alloc_anon(root_inode->i_sb); - if (res) { - res->d_flags |= DCACHE_RCUACCESS; + if (res) d_instantiate(res, root_inode); - } else { + else iput(root_inode); - } } return res; } @@ -2781,9 +2785,7 @@ static void __d_move(struct dentry *dent copy_name(dentry, target); target->d_hash.pprev = NULL; dentry->d_parent->d_lockref.count++; - if (dentry == old_parent) - dentry->d_flags |= DCACHE_RCUACCESS; - else + if (dentry != old_parent) /* wasn't IS_ROOT */ WARN_ON(!--old_parent->d_lockref.count); } else { target->d_parent = old_parent; --- a/fs/nsfs.c +++ b/fs/nsfs.c @@ -85,13 +85,12 @@ slow: inode->i_fop = &ns_file_operations; inode->i_private = ns; - dentry = d_alloc_pseudo(mnt->mnt_sb, &empty_name); + dentry = d_alloc_anon(mnt->mnt_sb); if (!dentry) { iput(inode); return ERR_PTR(-ENOMEM); } d_instantiate(dentry, inode); - dentry->d_flags |= DCACHE_RCUACCESS; dentry->d_fsdata = (void *)ns->ops; d = atomic_long_cmpxchg(&ns->stashed, 0, (unsigned long)dentry); if (d) { --- a/include/linux/dcache.h +++ b/include/linux/dcache.h @@ -176,7 +176,6 @@ struct dentry_operations { * typically using d_splice_alias. */ #define DCACHE_REFERENCED 0x00000040 /* Recently used, don't discard. */ -#define DCACHE_RCUACCESS 0x00000080 /* Entry has ever been RCU-visible */ #define DCACHE_CANT_MOUNT 0x00000100 #define DCACHE_GENOCIDE 0x00000200 @@ -217,6 +216,7 @@ struct dentry_operations { #define DCACHE_PAR_LOOKUP 0x10000000 /* being looked up (with parent locked shared) */ #define DCACHE_DENTRY_CURSOR 0x20000000 +#define DCACHE_NORCU 0x40000000 /* No RCU delay for freeing */ extern seqlock_t rename_lock;