This is a note to let you know that I've just added the patch titled bdi: Do not use freezable workqueue to the 4.14-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: bdi-do-not-use-freezable-workqueue.patch and it can be found in the queue-4.14 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From a2b90f11217790ec0964ba9c93a4abb369758c26 Mon Sep 17 00:00:00 2001 From: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx> Date: Fri, 4 Oct 2019 13:00:24 +0300 Subject: bdi: Do not use freezable workqueue From: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx> commit a2b90f11217790ec0964ba9c93a4abb369758c26 upstream. A removable block device, such as NVMe or SSD connected over Thunderbolt can be hot-removed any time including when the system is suspended. When device is hot-removed during suspend and the system gets resumed, kernel first resumes devices and then thaws the userspace including freezable workqueues. What happens in that case is that the NVMe driver notices that the device is unplugged and removes it from the system. This ends up calling bdi_unregister() for the gendisk which then schedules wb_workfn() to be run one more time. However, since the bdi_wq is still frozen flush_delayed_work() call in wb_shutdown() blocks forever halting system resume process. User sees this as hang as nothing is happening anymore. Triggering sysrq-w reveals this: Workqueue: nvme-wq nvme_remove_dead_ctrl_work [nvme] Call Trace: ? __schedule+0x2c5/0x630 ? wait_for_completion+0xa4/0x120 schedule+0x3e/0xc0 schedule_timeout+0x1c9/0x320 ? resched_curr+0x1f/0xd0 ? wait_for_completion+0xa4/0x120 wait_for_completion+0xc3/0x120 ? wake_up_q+0x60/0x60 __flush_work+0x131/0x1e0 ? flush_workqueue_prep_pwqs+0x130/0x130 bdi_unregister+0xb9/0x130 del_gendisk+0x2d2/0x2e0 nvme_ns_remove+0xed/0x110 [nvme_core] nvme_remove_namespaces+0x96/0xd0 [nvme_core] nvme_remove+0x5b/0x160 [nvme] pci_device_remove+0x36/0x90 device_release_driver_internal+0xdf/0x1c0 nvme_remove_dead_ctrl_work+0x14/0x30 [nvme] process_one_work+0x1c2/0x3f0 worker_thread+0x48/0x3e0 kthread+0x100/0x140 ? current_work+0x30/0x30 ? kthread_park+0x80/0x80 ret_from_fork+0x35/0x40 This is not limited to NVMes so exactly same issue can be reproduced by hot-removing SSD (over Thunderbolt) while the system is suspended. Prevent this from happening by removing WQ_FREEZABLE from bdi_wq. Reported-by: AceLan Kao <acelan.kao@xxxxxxxxxxxxx> Link: https://marc.info/?l=linux-kernel&m=138695698516487 Link: https://bugzilla.kernel.org/show_bug.cgi?id=204385 Link: https://lore.kernel.org/lkml/20191002122136.GD2819@xxxxxxxxxxxxxxxxxx/#t Acked-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx> Signed-off-by: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx> Signed-off-by: Jens Axboe <axboe@xxxxxxxxx> Cc: Macpaul Lin <macpaul.lin@xxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- mm/backing-dev.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) --- a/mm/backing-dev.c +++ b/mm/backing-dev.c @@ -247,8 +247,8 @@ static int __init default_bdi_init(void) { int err; - bdi_wq = alloc_workqueue("writeback", WQ_MEM_RECLAIM | WQ_FREEZABLE | - WQ_UNBOUND | WQ_SYSFS, 0); + bdi_wq = alloc_workqueue("writeback", WQ_MEM_RECLAIM | WQ_UNBOUND | + WQ_SYSFS, 0); if (!bdi_wq) return -ENOMEM; Patches currently in stable-queue which might be from mika.westerberg@xxxxxxxxxxxxxxx are queue-4.14/bdi-do-not-use-freezable-workqueue.patch