From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tejun Heo Subject: [PATCH 1/5] writeback: laptop_mode_timer_fn() needs rcu_read_lock() around bdi_writeback iteration Date: Tue, 29 Sep 2015 12:47:50 -0400 Message-ID: <1443545274-18787-2-git-send-email-tj@kernel.org> References: <1443545274-18787-1-git-send-email-tj@kernel.org> Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=sender:from:to:cc:subject:date:message-id:in-reply-to:references; bh=5RHNjeLDcITapkDlrzRPwA7GXnid9j15um2y5TwD97c=; b=OArxD9z8olAi9dBxKHYN8/JzJxPykQq8KLhkfOmuRN4CXR4xdEkuR1kbts/J0PEPer chEGV/8KGiWStXzqTAdjDXkib23ZnGslQz98/I0EomtzFQQI5Nhg9maJNucwtUUjvHgX WYV3lDAPLk1AgaaTTwrEGDKaMewe1ADc9ahJgR1h9HIKKgAvUGdFVqk1FbRmUFQYK3Iy aGDWjjgUm8CeIKNbwbqRsFf/054aEt9EF+xBj5XCQd4HNpXlqhPvnmmUllxpU+UI4tE+ 5fJUMCgNXLgSoCuD73zSdYC/BSlFYquiYo2dOOfYc6QyNQKeAy3FVHyDD+Q3MC6xPA9m +5TQ== In-Reply-To: <1443545274-18787-1-git-send-email-tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org> Sender: cgroups-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: axboe-tSWWG44O7X1aa/9Udqfwiw@public.gmane.org Cc: linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, tytso-3s7WtUTddSA@public.gmane.org, dedekind1-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, decui-0li6OtcxBFHby3iVrkZq2A@public.gmane.org, kernel-team-b10kYP2dOMg@public.gmane.org, Tejun Heo laptop_mode_timer_fn() was using bdi_for_each_wb() without the required RCU locking leading to the following warning. WARNING: CPU: 0 PID: 0 at include/linux/backing-dev.h:415 laptop_mode_timer_fn+0x106/0x170() ... Call Trace: [] dump_stack+0x4e/0x82 [] warn_slowpath_common+0x82/0xc0 [] warn_slowpath_null+0x1a/0x20 [] laptop_mode_timer_fn+0x106/0x170 [] call_timer_fn+0xb3/0x2f0 [] run_timer_softirq+0x205/0x370 [] __do_softirq+0xd4/0x460 [] irq_exit+0x89/0xa0 [] smp_apic_timer_interrupt+0x42/0x50 [] apic_timer_interrupt+0x84/0x90 ... Fix it by adding rcu_read_lock() around the iteration. Signed-off-by: Tejun Heo Fixes: a06fd6b10228 ("writeback: make laptop_mode_timer_fn() handle multiple bdi_writeback's") --- mm/page-writeback.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/mm/page-writeback.c b/mm/page-writeback.c index 0a931cd..902e5f2 100644 --- a/mm/page-writeback.c +++ b/mm/page-writeback.c @@ -1965,10 +1965,12 @@ void laptop_mode_timer_fn(unsigned long data) if (!bdi_has_dirty_io(&q->backing_dev_info)) return; + rcu_read_lock(); bdi_for_each_wb(wb, &q->backing_dev_info, &iter, 0) if (wb_has_dirty_io(wb)) wb_start_writeback(wb, nr_pages, true, WB_REASON_LAPTOP_TIMER); + rcu_read_unlock(); } /* -- 2.4.3