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=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=unavailable 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 CE0A6C43381 for ; Fri, 22 Mar 2019 13:01:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9D90C2075E for ; Fri, 22 Mar 2019 13:01:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1553259666; bh=ItaD8kDeaVxFGMcQUrCQHFrofUl3jtpJvFiM69Dqang=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=JazpZRKJSTEx2hFTsKql4VK8nYJaym0bxLYRy3/L+luecpSZj6481z8zpLugv0x0Y VWiKmviGaZ3vR3sGjpY2OkJQU9ozxJXi9cgqHKMVyDJL8TVMH2TjhNUgkIlJYnWDKY ZA4WCtnmZzAiM21McXmEmN2+2qBXy5sCRzZoWPkw= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731228AbfCVNBA (ORCPT ); Fri, 22 Mar 2019 09:01:00 -0400 Received: from mail.kernel.org ([198.145.29.99]:46380 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731299AbfCVLnh (ORCPT ); Fri, 22 Mar 2019 07:43:37 -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 540A921916; Fri, 22 Mar 2019 11:43:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1553255016; bh=ItaD8kDeaVxFGMcQUrCQHFrofUl3jtpJvFiM69Dqang=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Gk7UngINHf80Lcrqg0zniNYHXVVU9+Sq/Qvntz6z17cMBmYcGW+uH9McBb7NIWPNY toyC6dne71y4UXqK0M+FFHm286adALjFstPMZasQx7//u+hKgQpM52/EccasXNVU4/ ThPQc53EgfqmRJii2RQeCAGJm3nH7eubPt74ManU= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Varad Gautam , Zheng Wang , Brandon Schwartz , David Woodhouse , Maximilian Heyne , Stefan Nuernberger , Amit Shah , Linus Torvalds , Al Viro , Christian Brauner , "Eric W. Biederman" , Matthew Wilcox , Eric Biggers , Al Viro , Nicolas Pernas Maradei Subject: [PATCH 4.9 063/118] fs/devpts: always delete dcache dentry-s in dput() Date: Fri, 22 Mar 2019 12:15:35 +0100 Message-Id: <20190322111221.116818757@linuxfoundation.org> X-Mailer: git-send-email 2.21.0 In-Reply-To: <20190322111215.873964544@linuxfoundation.org> References: <20190322111215.873964544@linuxfoundation.org> User-Agent: quilt/0.65 X-stable: review X-Patchwork-Hint: ignore MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org 4.9-stable review patch. If anyone has any objections, please let me know. ------------------ From: Varad Gautam commit 73052b0daee0b750b39af18460dfec683e4f5887 upstream. d_delete only unhashes an entry if it is reached with dentry->d_lockref.count != 1. Prior to commit 8ead9dd54716 ("devpts: more pty driver interface cleanups"), d_delete was called on a dentry from devpts_pty_kill with two references held, which would trigger the unhashing, and the subsequent dputs would release it. Commit 8ead9dd54716 reworked devpts_pty_kill to stop acquiring the second reference from d_find_alias, and the d_delete call left the dentries still on the hashed list without actually ever being dropped from dcache before explicit cleanup. This causes the number of negative dentries for devpts to pile up, and an `ls /dev/pts` invocation can take seconds to return. Provide always_delete_dentry() from simple_dentry_operations as .d_delete for devpts, to make the dentry be dropped from dcache. Without this cleanup, the number of dentries in /dev/pts/ can be grown arbitrarily as: `python -c 'import pty; pty.spawn(["ls", "/dev/pts"])'` A systemtap probe on dcache_readdir to count d_subdirs shows this count to increase with each pty spawn invocation above: probe kernel.function("dcache_readdir") { subdirs = &@cast($file->f_path->dentry, "dentry")->d_subdirs; p = subdirs; p = @cast(p, "list_head")->next; i = 0 while (p != subdirs) { p = @cast(p, "list_head")->next; i = i+1; } printf("number of dentries: %d\n", i); } Fixes: 8ead9dd54716 ("devpts: more pty driver interface cleanups") Signed-off-by: Varad Gautam Reported-by: Zheng Wang Reported-by: Brandon Schwartz Root-caused-by: Maximilian Heyne Root-caused-by: Nicolas Pernas Maradei CC: David Woodhouse CC: Maximilian Heyne CC: Stefan Nuernberger CC: Amit Shah CC: Linus Torvalds CC: Greg Kroah-Hartman CC: Al Viro CC: Christian Brauner CC: Eric W. Biederman CC: Matthew Wilcox CC: Eric Biggers CC: # 4.9+ Signed-off-by: Al Viro Signed-off-by: Greg Kroah-Hartman --- fs/devpts/inode.c | 1 + 1 file changed, 1 insertion(+) --- a/fs/devpts/inode.c +++ b/fs/devpts/inode.c @@ -396,6 +396,7 @@ devpts_fill_super(struct super_block *s, s->s_blocksize_bits = 10; s->s_magic = DEVPTS_SUPER_MAGIC; s->s_op = &devpts_sops; + s->s_d_op = &simple_dentry_operations; s->s_time_gran = 1; error = -ENOMEM;