From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.linuxfoundation.org ([140.211.169.12]:55198 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727690AbeI0P2Q (ORCPT ); Thu, 27 Sep 2018 11:28:16 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, KJ Tsanaktsidis , Andrew Morton , Michal Hocko , Gargi Sharma , Rik van Riel , Oleg Nesterov Subject: [PATCH 4.18 50/88] fork: report pid exhaustion correctly Date: Thu, 27 Sep 2018 11:03:31 +0200 Message-Id: <20180927090306.894709743@linuxfoundation.org> In-Reply-To: <20180927090300.631426620@linuxfoundation.org> References: <20180927090300.631426620@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org List-ID: 4.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: KJ Tsanaktsidis commit f83606f5eb007adc33bc8541ede00590f477bdeb upstream. Make the clone and fork syscalls return EAGAIN when the limit on the number of pids /proc/sys/kernel/pid_max is exceeded. Currently, when the pid_max limit is exceeded, the kernel will return ENOSPC from the fork and clone syscalls. This is contrary to the documented behaviour, which explicitly calls out the pid_max case as one where EAGAIN should be returned. It also leads to really confusing error messages in userspace programs which will complain about a lack of disk space when they fail to create processes/threads for this reason. This error is being returned because alloc_pid() uses the idr api to find a new pid; when there are none available, idr_alloc_cyclic() returns -ENOSPC, and this is being propagated back to userspace. This behaviour has been broken before, and was explicitly fixed in commit 35f71bc0a09a ("fork: report pid reservation failure properly"), so I think -EAGAIN is definitely the right thing to return in this case. The current behaviour change dates from commit 95846ecf9dac ("pid: replace pid bitmap implementation with IDR AIP") and was I believe unintentional. This patch has no impact on the case where allocating a pid fails because the child reaper for the namespace is dead; that case will still return -ENOMEM. Link: http://lkml.kernel.org/r/20180903111016.46461-1-ktsanaktsidis@zendesk.com Fixes: 95846ecf9dac ("pid: replace pid bitmap implementation with IDR AIP") Signed-off-by: KJ Tsanaktsidis Reviewed-by: Andrew Morton Acked-by: Michal Hocko Cc: Gargi Sharma Cc: Rik van Riel Cc: Oleg Nesterov Cc: Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman --- kernel/pid.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/kernel/pid.c +++ b/kernel/pid.c @@ -195,7 +195,7 @@ struct pid *alloc_pid(struct pid_namespa idr_preload_end(); if (nr < 0) { - retval = nr; + retval = (nr == -ENOSPC) ? -EAGAIN : nr; goto out_free; }