From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.linuxfoundation.org ([140.211.169.12]:59988 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753992AbdGJPZL (ORCPT ); Mon, 10 Jul 2017 11:25:11 -0400 Subject: Patch "sched/numa: Use down_read_trylock() for the mmap_sem" has been added to the 4.12-stable tree To: vbabka@suse.cz, gregkh@linuxfoundation.org, mgorman@techsingularity.net, mingo@kernel.org, peterz@infradead.org, riel@redhat.com, tglx@linutronix.de, torvalds@linux-foundation.org Cc: , From: Date: Mon, 10 Jul 2017 17:24:57 +0200 Message-ID: <1499700297186204@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 sched/numa: Use down_read_trylock() for the mmap_sem to the 4.12-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: sched-numa-use-down_read_trylock-for-the-mmap_sem.patch and it can be found in the queue-4.12 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let know about it. >>From 8655d5497735b288f8a9b458bd22e7d1bf95bb61 Mon Sep 17 00:00:00 2001 From: Vlastimil Babka Date: Mon, 15 May 2017 15:13:16 +0200 Subject: sched/numa: Use down_read_trylock() for the mmap_sem From: Vlastimil Babka commit 8655d5497735b288f8a9b458bd22e7d1bf95bb61 upstream. A customer has reported a soft-lockup when running an intensive memory stress test, where the trace on multiple CPU's looks like this: RIP: 0010:[] [] native_queued_spin_lock_slowpath+0x10e/0x190 ... Call Trace: [] queued_spin_lock_slowpath+0x7/0xa [] change_protection_range+0x3b1/0x930 [] change_prot_numa+0x18/0x30 [] task_numa_work+0x1fe/0x310 [] task_work_run+0x72/0x90 Further investigation showed that the lock contention here is pmd_lock(). The task_numa_work() function makes sure that only one thread is let to perform the work in a single scan period (via cmpxchg), but if there's a thread with mmap_sem locked for writing for several periods, multiple threads in task_numa_work() can build up a convoy waiting for mmap_sem for read and then all get unblocked at once. This patch changes the down_read() to the trylock version, which prevents the build up. For a workload experiencing mmap_sem contention, it's probably better to postpone the NUMA balancing work anyway. This seems to have fixed the soft lockups involving pmd_lock(), which is in line with the convoy theory. Signed-off-by: Vlastimil Babka Signed-off-by: Peter Zijlstra (Intel) Acked-by: Rik van Riel Acked-by: Mel Gorman Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/20170515131316.21909-1-vbabka@suse.cz Signed-off-by: Ingo Molnar Signed-off-by: Mel Gorman Signed-off-by: Greg Kroah-Hartman --- kernel/sched/fair.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -2469,7 +2469,8 @@ void task_numa_work(struct callback_head return; - down_read(&mm->mmap_sem); + if (!down_read_trylock(&mm->mmap_sem)) + return; vma = find_vma(mm, start); if (!vma) { reset_ptenuma_scan(p); Patches currently in stable-queue which might be from vbabka@suse.cz are queue-4.12/sched-numa-use-down_read_trylock-for-the-mmap_sem.patch