Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754676Ab2FSScX (ORCPT ); Tue, 19 Jun 2012 14:32:23 -0400 Received: from mail-lb0-f174.google.com ([209.85.217.174]:32985 "EHLO mail-lb0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753101Ab2FSScV (ORCPT ); Tue, 19 Jun 2012 14:32:21 -0400 MIME-Version: 1.0 Date: Wed, 20 Jun 2012 00:02:19 +0530 Message-ID: Subject: [RFC][RT][PATCH] mm: Do not use stop_machine() for __zone_pcp_udpate() for CONFIG_PREEMPT_RT_FULL From: Aaditya Kumar To: Thomas Gleixner Cc: linux-kernel@vger.kernel.org, rostedt@goodmis.org, mingo@kernel.org, C.Emde@osadl.org, jkacur@redhat.com, frank.rowand@am.sony.com, tim.bird@am.sony.com, takuzo.ohara@ap.sony.com, kan.iibuchi@jp.sony.com Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2511 Lines: 70 The code path of __zone_pcp_update() has following locks, which in CONFIG_PREEMPT_RT_FULL=y are rt-mutex. - pa_lock locked by cpu_lock_irqsave() - zone->lock locked by free_pcppages_bulk() Since __zone_pcp_update() is called from stop_machine(), so with CONFIG_PREEMPT_RT_FULL=y we get following backtrace when __zone_pcp_update() is called during memory hot plugging while doing heavy file I/O. I think stop_machine() may not be required for calling __zone_pcp_update() in case of CONFIG_PREEMPT_RT_FULL=y as acquiring pa_lock in __zone_pcp_update() should be sufficient to isolate pcp pages and to setup per cpu pagesets. Can someone please let me know if am missing anything here? The backtrace that this patch fixes: BUG: scheduling while atomic: migration/0/7/0x00000002 Modules linked in: v2p Backtrace: [<800111a0>] (dump_backtrace+0x0/0x10c) from [<802d7b7c>] (dump_stack+0x18/0x1c) r6:80c8fc28 r5:80c8f9a0 r4:00000000 r3:60000013 [<802d7b64>] (dump_stack+0x0/0x1c) from [<8001e81c>] (__schedule_bug+0x64/0x74) [<8001e7b8>] (__schedule_bug+0x0/0x74) from [<802d7fa0>] (__schedule+0x68/0x604) r4:8051bf00 r3:00000000 [<802d7f38>] (__schedule+0x0/0x604) from [<802d8a78>] (schedule+0x98/0xbc) [<802d89e0>] (schedule+0x0/0xbc) from [<802d9e14>] (rt_spin_lock_slowlock+0x168/0x240) r4:805228f4 r3:00000000 [<802d9cac>] (rt_spin_lock_slowlock+0x0/0x240) from [<802da234>] (rt_spin_lock+0x10/0x14) [<802da224>] (rt_spin_lock+0x0/0x14) from [<8008694c>] (__zone_pcp_update+0x58/0xd8) [<800868f4>] (__zone_pcp_update+0x0/0xd8) from [<800603ec>] (stop_machine_cpu_stop+0xb0/0x104) [<8006033c>] (stop_machine_cpu_stop+0x0/0x104) from [<80060200>] (cpu_stopper_thread+0xd4/0x188) Signed-off-by: Aaditya Kumar --- mm/page_alloc.c | 4 4 + 0 - 0 ! 1 file changed, 4 insertions(+) Index: b/mm/page_alloc.c =================================================================== --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -3868,7 +3868,11 @@ static int __zone_pcp_update(void *data) void zone_pcp_update(struct zone *zone) { +#ifndef CONFIG_PREEMPT_RT_FULL stop_machine(__zone_pcp_update, zone, NULL); +#else + __zone_pcp_update(zone); +#endif } static __meminit void zone_pcp_init(struct zone *zone) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/