3.2-stable review patch. If anyone has any objections, please let me know.
------------------ From: Rabin Vincent <[email protected]> commit 2673b4cf5d59c3ee5e0c12f6d734d38770324dc4 upstream. While 7a401a972df8e18 ("backing-dev: ensure wakeup_timer is deleted") addressed the problem of the bdi being freed with a queued wakeup timer, there are other races that could happen if the wakeup timer expires after/during bdi_unregister(), before bdi_destroy() is called. wakeup_timer_fn() could attempt to wakeup a task which has already has been freed, or could access a NULL bdi->dev via the wake_forker_thread tracepoint. Cc: Jens Axboe <[email protected]> Reported-by: Chanho Min <[email protected]> Reviewed-by: Namjae Jeon <[email protected]> Signed-off-by: Rabin Vincent <[email protected]> Signed-off-by: Wu Fengguang <[email protected]> Signed-off-by: Greg Kroah-Hartman <[email protected]> --- mm/backing-dev.c | 25 +++++++++++++++++++------ 1 file changed, 19 insertions(+), 6 deletions(-) --- a/mm/backing-dev.c +++ b/mm/backing-dev.c @@ -318,7 +318,7 @@ static void wakeup_timer_fn(unsigned lon if (bdi->wb.task) { trace_writeback_wake_thread(bdi); wake_up_process(bdi->wb.task); - } else { + } else if (bdi->dev) { /* * When bdi tasks are inactive for long time, they are killed. * In this case we have to wake-up the forker thread which @@ -584,6 +584,8 @@ EXPORT_SYMBOL(bdi_register_dev); */ static void bdi_wb_shutdown(struct backing_dev_info *bdi) { + struct task_struct *task; + if (!bdi_cap_writeback_dirty(bdi)) return; @@ -604,9 +606,14 @@ static void bdi_wb_shutdown(struct backi * unfreeze of the thread before calling kthread_stop(), otherwise * it would never exet if it is currently stuck in the refrigerator. */ - if (bdi->wb.task) { - thaw_process(bdi->wb.task); - kthread_stop(bdi->wb.task); + spin_lock_bh(&bdi->wb_lock); + task = bdi->wb.task; + bdi->wb.task = NULL; + spin_unlock_bh(&bdi->wb_lock); + + if (task) { + thaw_process(task); + kthread_stop(task); } } @@ -627,7 +634,9 @@ static void bdi_prune_sb(struct backing_ void bdi_unregister(struct backing_dev_info *bdi) { - if (bdi->dev) { + struct device *dev = bdi->dev; + + if (dev) { bdi_set_min_ratio(bdi, 0); trace_writeback_bdi_unregister(bdi); bdi_prune_sb(bdi); @@ -636,8 +645,12 @@ void bdi_unregister(struct backing_dev_i if (!bdi_cap_flush_forker(bdi)) bdi_wb_shutdown(bdi); bdi_debug_unregister(bdi); - device_unregister(bdi->dev); + + spin_lock_bh(&bdi->wb_lock); bdi->dev = NULL; + spin_unlock_bh(&bdi->wb_lock); + + device_unregister(dev); } } EXPORT_SYMBOL(bdi_unregister); -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
