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SubjectRe: [PATCH 1/5] writeback: laptop_mode_timer_fn() needs rcu_read_lock() around bdi_writeback iteration
On Tue 29-09-15 12:47:50, Tejun Heo wrote:
> 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:
> <IRQ> [<ffffffff81480cdc>] dump_stack+0x4e/0x82
> [<ffffffff81051912>] warn_slowpath_common+0x82/0xc0
> [<ffffffff81051a0a>] warn_slowpath_null+0x1a/0x20
> [<ffffffff8115f0e6>] laptop_mode_timer_fn+0x106/0x170
> [<ffffffff810ca8e3>] call_timer_fn+0xb3/0x2f0
> [<ffffffff810cad25>] run_timer_softirq+0x205/0x370
> [<ffffffff81056854>] __do_softirq+0xd4/0x460
> [<ffffffff81056d69>] irq_exit+0x89/0xa0
> [<ffffffff8185a892>] smp_apic_timer_interrupt+0x42/0x50
> [<ffffffff81858a44>] apic_timer_interrupt+0x84/0x90
> ...
>
> Fix it by adding rcu_read_lock() around the iteration.
>
> Signed-off-by: Tejun Heo <tj@kernel.org>
> Fixes: a06fd6b10228 ("writeback: make laptop_mode_timer_fn() handle multiple bdi_writeback's")

Looks good. You can add:

Reviewed-by: Jan Kara <jack@suse.com>

Honza
> ---
> 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
>
> --
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--
Jan Kara <jack@suse.com>
SUSE Labs, CR


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