From 8a32c441c1609f80e55df75422324a1151208f40 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Mon, 21 Nov 2011 12:32:23 -0800 Subject: freezer: implement and use kthread_freezable_should_stop() Writeback and thinkpad_acpi have been using thaw_process() to prevent deadlock between the freezer and kthread_stop(); unfortunately, this is inherently racy - nothing prevents freezing from happening between thaw_process() and kthread_stop(). This patch implements kthread_freezable_should_stop() which enters refrigerator if necessary but is guaranteed to return if kthread_stop() is invoked. Both thaw_process() users are converted to use the new function. Note that this deadlock condition exists for many of freezable kthreads. They need to be converted to use the new should_stop or freezable workqueue. Tested with synthetic test case. Signed-off-by: Tejun Heo Acked-by: Henrique de Moraes Holschuh Cc: Jens Axboe Cc: Oleg Nesterov --- mm/backing-dev.c | 8 ++------ 1 file changed, 2 insertions(+), 6 deletions(-) (limited to 'mm/backing-dev.c') diff --git a/mm/backing-dev.c b/mm/backing-dev.c index 71034f41a2ba..7ba8feae11b8 100644 --- a/mm/backing-dev.c +++ b/mm/backing-dev.c @@ -600,14 +600,10 @@ static void bdi_wb_shutdown(struct backing_dev_info *bdi) /* * Finally, kill the kernel thread. We don't need to be RCU - * safe anymore, since the bdi is gone from visibility. Force - * unfreeze of the thread before calling kthread_stop(), otherwise - * it would never exet if it is currently stuck in the refrigerator. + * safe anymore, since the bdi is gone from visibility. */ - if (bdi->wb.task) { - thaw_process(bdi->wb.task); + if (bdi->wb.task) kthread_stop(bdi->wb.task); - } } /* -- cgit v1.2.3 From 2673b4cf5d59c3ee5e0c12f6d734d38770324dc4 Mon Sep 17 00:00:00 2001 From: Rabin Vincent Date: Sun, 29 Jan 2012 12:17:33 -0600 Subject: backing-dev: fix wakeup timer races with bdi_unregister() 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: Cc: Jens Axboe Reported-by: Chanho Min Reviewed-by: Namjae Jeon Signed-off-by: Rabin Vincent Signed-off-by: Wu Fengguang --- mm/backing-dev.c | 23 ++++++++++++++++++----- 1 file changed, 18 insertions(+), 5 deletions(-) (limited to 'mm/backing-dev.c') diff --git a/mm/backing-dev.c b/mm/backing-dev.c index 7ba8feae11b8..dd8e2aafb07e 100644 --- a/mm/backing-dev.c +++ b/mm/backing-dev.c @@ -318,7 +318,7 @@ static void wakeup_timer_fn(unsigned long data) 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; @@ -602,8 +604,13 @@ static void bdi_wb_shutdown(struct backing_dev_info *bdi) * Finally, kill the kernel thread. We don't need to be RCU * safe anymore, since the bdi is gone from visibility. */ - if (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) + kthread_stop(task); } /* @@ -623,7 +630,9 @@ static void bdi_prune_sb(struct backing_dev_info *bdi) 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); @@ -632,8 +641,12 @@ void bdi_unregister(struct backing_dev_info *bdi) 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); -- cgit v1.2.3