From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.linuxfoundation.org ([140.211.169.12]:59963 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756454AbbGPRnY (ORCPT ); Thu, 16 Jul 2015 13:43:24 -0400 Subject: Patch "rcu: Correctly handle non-empty Tiny RCU callback list with none ready" has been added to the 4.1-stable tree To: paulmck@linux.vnet.ibm.com, gregkh@linuxfoundation.org, josh@joshtriplett.org Cc: , From: Date: Thu, 16 Jul 2015 10:43:02 -0700 Message-ID: <1437068582695@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=ANSI_X3.4-1968 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org List-ID: This is a note to let you know that I've just added the patch titled rcu: Correctly handle non-empty Tiny RCU callback list with none ready to the 4.1-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: rcu-correctly-handle-non-empty-tiny-rcu-callback-list-with-none-ready.patch and it can be found in the queue-4.1 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let know about it. >>From 6e91f8cb138625be96070b778d9ba71ce520ea7e Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Mon, 11 May 2015 11:13:05 -0700 Subject: rcu: Correctly handle non-empty Tiny RCU callback list with none ready From: "Paul E. McKenney" commit 6e91f8cb138625be96070b778d9ba71ce520ea7e upstream. If, at the time __rcu_process_callbacks() is invoked, there are callbacks in Tiny RCU's callback list, but none of them are ready to be invoked, the current list-management code will knit the non-ready callbacks out of the list. This can result in hangs and possibly worse. This commit therefore inserts a check for there being no callbacks that can be invoked immediately. This bug is unlikely to occur -- you have to get a new callback between the time rcu_sched_qs() or rcu_bh_qs() was called, but before we get to __rcu_process_callbacks(). It was detected by the addition of RCU-bh testing to rcutorture, which in turn was instigated by Iftekhar Ahmed's mutation testing. Although this bug was made much more likely by 915e8a4fe45e (rcu: Remove fastpath from __rcu_process_callbacks()), this did not cause the bug, but rather made it much more probable. That said, it takes more than 40 hours of rcutorture testing, on average, for this bug to appear, so this fix cannot be considered an emergency. Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett Signed-off-by: Greg Kroah-Hartman --- kernel/rcu/tiny.c | 5 +++++ 1 file changed, 5 insertions(+) --- a/kernel/rcu/tiny.c +++ b/kernel/rcu/tiny.c @@ -170,6 +170,11 @@ static void __rcu_process_callbacks(stru /* Move the ready-to-invoke callbacks to a local list. */ local_irq_save(flags); + if (rcp->donetail == &rcp->rcucblist) { + /* No callbacks ready, so just leave. */ + local_irq_restore(flags); + return; + } RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, rcp->qlen, -1)); list = rcp->rcucblist; rcp->rcucblist = *rcp->donetail; Patches currently in stable-queue which might be from paulmck@linux.vnet.ibm.com are queue-4.1/rcu-correctly-handle-non-empty-tiny-rcu-callback-list-with-none-ready.patch