From 9ad18ab938375502c03cf467abecbb77264c9475 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Tue, 29 Sep 2015 12:47:50 -0400 Subject: [PATCH] writeback: laptop_mode_timer_fn() needs rcu_read_lock() around bdi_writeback iteration 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") Reviewed-by: Jan Kara Signed-off-by: Jens Axboe --- mm/page-writeback.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/mm/page-writeback.c b/mm/page-writeback.c index 0a931cdd4f6b..902e5f215e57 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(); } /* -- 2.39.2