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x-ptr=pass x-ptr-helo=vger.kernel.org x-ptr-lookup=vger.kernel.org; x-return-mx=pass smtp.domain=vger.kernel.org smtp.result=pass smtp_org.domain=kernel.org smtp_org.result=pass smtp_is_org_domain=no header.domain=microsoft.com header.result=pass header_is_org_domain=yes Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S966031AbeCSRXT (ORCPT ); Mon, 19 Mar 2018 13:23:19 -0400 Received: from mail-by2nam01on0094.outbound.protection.outlook.com ([104.47.34.94]:45505 "EHLO NAM01-BY2-obe.outbound.protection.outlook.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S966379AbeCSQI7 (ORCPT ); Mon, 19 Mar 2018 12:08:59 -0400 From: Sasha Levin To: "linux-kernel@vger.kernel.org" , "stable@vger.kernel.org" CC: Vlastimil Babka , Peter Zijlstra , Linus Torvalds , Thomas Gleixner , Ingo Molnar , Sasha Levin Subject: [PATCH AUTOSEL for 4.4 063/167] sched/numa: Use down_read_trylock() for the mmap_sem Thread-Topic: [PATCH AUTOSEL for 4.4 063/167] sched/numa: Use down_read_trylock() for the mmap_sem Thread-Index: AQHTv5xDLpnoj7RWs0y+Tn4wFyDLtA== Date: Mon, 19 Mar 2018 16:06:40 +0000 Message-ID: <20180319160513.16384-63-alexander.levin@microsoft.com> References: <20180319160513.16384-1-alexander.levin@microsoft.com> In-Reply-To: <20180319160513.16384-1-alexander.levin@microsoft.com> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [52.168.54.252] x-ms-publictraffictype: Email x-microsoft-exchange-diagnostics: 1;DM5PR2101MB0965;7:mWu3cwwj91IcMWfv/mQQ6YBSCqIikiHYJbODy39GgbVj/Ut1NDvwC/BPBsN6Pa3WWCmzTTgZUihfGUMKniQshq6Ac97nwXbpkdCbXtp2QlYua52jSHMeTZr/WG5MT/vCa5Ox7HAeAmASSsfEfE87jwWXnmA8eDnObiuQq8KeqmhJQIE/Sr2OwB2SBPNxN3Ai9MyZjohrwVY8GWhKcxty/cXBYJIBGHvBnRpenO3fC4TkMdAwFWeNWA6uwrzLZKQ8;20:EQGfbfaAiiNfSieVFGqCc2rGB0J8USXxuxIXwGKCl40HgvoH0SNPOhHvfiCgHtPCzZxvOBRMaLVwcl+eFZrxTsho/v1YRd0kxWg7mkTrqkn9nbtpQm1VkjRDXvNKIRXVg/KM7LhoRAxMIf4efsXdkUvf1WsEc3T/Vi4k1D8Z/pk= x-ms-office365-filtering-ht: Tenant x-ms-office365-filtering-correlation-id: 61609005-fabf-4cf5-db6f-08d58db3b71f x-microsoft-antispam: UriScan:;BCL:0;PCL:0;RULEID:(7020095)(4652020)(48565401081)(5600026)(4604075)(3008032)(4534165)(4627221)(201703031133081)(201702281549075)(2017052603328)(7193020);SRVR:DM5PR2101MB0965; 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x-microsoft-antispam-message-info: LU/eJ6doMP7S3BKxuiN7I+5gfxlGf/GrI5TWpKLJxUcP95j7x9paLXCxRx1RRqH8mHfZBZjTqe8PRB1xKMZFgDuM8xcH/tAm6M0WNlaaQ3LxUlpk0o8yaDROv7n3ZxiiBK9Hsko5AawaFdrr9SdjVNuD0/tKmhDf/JWCks3a3fe70W/5bFNzjytkUlJX06AfZTaDnBHObDJYs/3Mng8mucqAhe4JSY3lKjkwTnIitJ0y1b76JFqgcwB1vCOeYQ/6NjXqcoUzlYBhWu4j+jZLuBl+1o+rbxWhMCL0pQmNKC3VeGbxaSMA3yTFgaHnEoTRqiMqVC3hzp1OtqmpYgkMWA== spamdiagnosticoutput: 1:99 spamdiagnosticmetadata: NSPM Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: microsoft.com X-MS-Exchange-CrossTenant-Network-Message-Id: 61609005-fabf-4cf5-db6f-08d58db3b71f X-MS-Exchange-CrossTenant-originalarrivaltime: 19 Mar 2018 16:06:40.0755 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 72f988bf-86f1-41af-91ab-2d7cd011db47 X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM5PR2101MB0965 Sender: stable-owner@vger.kernel.org X-Mailing-List: stable@vger.kernel.org X-getmail-retrieved-from-mailbox: INBOX X-Mailing-List: linux-kernel@vger.kernel.org List-ID: From: Vlastimil Babka [ Upstream commit 8655d5497735b288f8a9b458bd22e7d1bf95bb61 ] 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 per= form the work in a single scan period (via cmpxchg), but if there's a thread wit= h 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 th= en all get unblocked at once. This patch changes the down_read() to the trylock version, which prevents t= he build up. For a workload experiencing mmap_sem contention, it's probably be= tter to postpone the NUMA balancing work anyway. This seems to have fixed the so= ft 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: Sasha Levin --- kernel/sched/fair.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 812069b66f47..3b136fb4422c 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -2223,7 +2223,8 @@ void task_numa_work(struct callback_head *work) return; =20 =20 - down_read(&mm->mmap_sem); + if (!down_read_trylock(&mm->mmap_sem)) + return; vma =3D find_vma(mm, start); if (!vma) { reset_ptenuma_scan(p); --=20 2.14.1