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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E33FAC61D97 for ; Fri, 24 Nov 2023 06:05:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232584AbjKXGF2 (ORCPT ); Fri, 24 Nov 2023 01:05:28 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57108 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231393AbjKXGEU (ORCPT ); Fri, 24 Nov 2023 01:04:20 -0500 Received: from zeniv.linux.org.uk (zeniv.linux.org.uk [IPv6:2a03:a000:7:0:5054:ff:fe1c:15ff]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0974410D3; Thu, 23 Nov 2023 22:04:27 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=linux.org.uk; s=zeniv-20220401; h=Sender:Content-Transfer-Encoding: MIME-Version:References:In-Reply-To:Message-Id:Date:Subject:Cc:To:From: Reply-To:Content-Type:Content-ID:Content-Description; bh=jw2SmoPh0qPYG8JBwFCByN8FOehIviEhno/pqpGWIrg=; b=SOooeC54qTWTsfPph2jbWrQ7fC IZfv8eynAFwpniQ6EVVIcHNhLUtIZmc8H6J6/R+AH7UXWx0DJ/TzCr+kBPQXc0WsbhN4iHA62sEl6 CaPKDJvDjK1nuWbYb/Azzr/muuI2Ra5FDaqmY++7uffeOWjZVPEgpYCRATNSWPydSNtnCsemwTabT ouIYMERGYA82q287yUEz3UBUAxQp8qg1X9yKIs7p3wD75+aOXvwHKcWUtTC4SHQXDjZILGupHzB+c 7r/xNymhRWW9SojOiGdrtd4rD0rJF/HcU6MEJts+OFssmsblcKLvupYUuDy6eOM/w7srYFBs22z9u no52taJA==; Received: from viro by zeniv.linux.org.uk with local (Exim 4.96 #2 (Red Hat Linux)) id 1r6PIf-002Puk-2B; Fri, 24 Nov 2023 06:04:25 +0000 From: Al Viro To: linux-fsdevel@vger.kernel.org Cc: Linus Torvalds , Christian Brauner , linux-kernel@vger.kernel.org Subject: [PATCH v3 13/21] Call retain_dentry() with refcount 0 Date: Fri, 24 Nov 2023 06:04:14 +0000 Message-Id: <20231124060422.576198-13-viro@zeniv.linux.org.uk> X-Mailer: git-send-email 2.40.1 In-Reply-To: <20231124060422.576198-1-viro@zeniv.linux.org.uk> References: <20231124060200.GR38156@ZenIV> <20231124060422.576198-1-viro@zeniv.linux.org.uk> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: Al Viro Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Instead of bumping it from 0 to 1, calling retain_dentry(), then decrementing it back to 0 (with ->d_lock held all the way through), just leave refcount at 0 through all of that. It will have a visible effect for ->d_delete() - now it can be called with refcount 0 instead of 1 and it can no longer play silly buggers with dropping/regaining ->d_lock. Not that any in-tree instances tried to (it's pretty hard to get right). Any out-of-tree ones will have to adjust (assuming they need any changes). Note that we do not need to extend rcu-critical area here - we have verified that refcount is non-negative after having grabbed ->d_lock, so nobody will be able to free dentry until they get into __dentry_kill(), which won't happen until they manage to grab ->d_lock. Reviewed-by: Christian Brauner Signed-off-by: Al Viro --- Documentation/filesystems/porting.rst | 8 ++++++++ fs/dcache.c | 10 ++-------- 2 files changed, 10 insertions(+), 8 deletions(-) diff --git a/Documentation/filesystems/porting.rst b/Documentation/filesystems/porting.rst index 331405f4b29f..3714efcb6f65 100644 --- a/Documentation/filesystems/porting.rst +++ b/Documentation/filesystems/porting.rst @@ -1070,3 +1070,11 @@ The list of children anchored in parent dentry got turned into hlist now. Field names got changed (->d_children/->d_sib instead of ->d_subdirs/->d_child for anchor/entries resp.), so any affected places will be immediately caught by compiler. + +--- + +**mandatory** + + ->d_delete() instances are now called for dentries with ->d_lock held +and refcount equal to 0. They are not permitted to drop/regain ->d_lock. +None of in-tree instances did anything of that sort. Make sure yours do not... diff --git a/fs/dcache.c b/fs/dcache.c index 80992e49561c..8ce0fe70f303 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -888,15 +888,14 @@ void dput(struct dentry *dentry) } /* Slow case: now with the dentry lock held */ - dentry->d_lockref.count = 1; rcu_read_unlock(); if (likely(retain_dentry(dentry))) { - dentry->d_lockref.count--; spin_unlock(&dentry->d_lock); return; } + dentry->d_lockref.count = 1; dentry = dentry_kill(dentry); } } @@ -921,13 +920,8 @@ void dput_to_list(struct dentry *dentry, struct list_head *list) return; } rcu_read_unlock(); - dentry->d_lockref.count = 1; - if (!retain_dentry(dentry)) { - --dentry->d_lockref.count; + if (!retain_dentry(dentry)) to_shrink_list(dentry, list); - } else { - --dentry->d_lockref.count; - } spin_unlock(&dentry->d_lock); } -- 2.39.2