On Tue, Nov 12, 2024 at 09:36:40AM +0100, Marek Szyprowski wrote: > On 29.10.2024 16:58, Ming Lei wrote: > > On Tue, Oct 29, 2024 at 12:13:35PM +0100, Marek Szyprowski wrote: > >> On 25.10.2024 02:37, Ming Lei wrote: > >>> Recently we got several deadlock report[1][2][3] caused by > >>> blk_mq_freeze_queue and blk_enter_queue(). > >>> > >>> Turns out the two are just like acquiring read/write lock, so model them > >>> as read/write lock for supporting lockdep: > >>> > >>> 1) model q->q_usage_counter as two locks(io and queue lock) > >>> > >>> - queue lock covers sync with blk_enter_queue() > >>> > >>> - io lock covers sync with bio_enter_queue() > >>> > >>> 2) make the lockdep class/key as per-queue: > >>> > >>> - different subsystem has very different lock use pattern, shared lock > >>> class causes false positive easily > >>> > >>> - freeze_queue degrades to no lock in case that disk state becomes DEAD > >>> because bio_enter_queue() won't be blocked any more > >>> > >>> - freeze_queue degrades to no lock in case that request queue becomes dying > >>> because blk_enter_queue() won't be blocked any more > >>> > >>> 3) model blk_mq_freeze_queue() as acquire_exclusive & try_lock > >>> - it is exclusive lock, so dependency with blk_enter_queue() is covered > >>> > >>> - it is trylock because blk_mq_freeze_queue() are allowed to run > >>> concurrently > >>> > >>> 4) model blk_enter_queue() & bio_enter_queue() as acquire_read() > >>> - nested blk_enter_queue() are allowed > >>> > >>> - dependency with blk_mq_freeze_queue() is covered > >>> > >>> - blk_queue_exit() is often called from other contexts(such as irq), and > >>> it can't be annotated as lock_release(), so simply do it in > >>> blk_enter_queue(), this way still covered cases as many as possible > >>> > >>> With lockdep support, such kind of reports may be reported asap and > >>> needn't wait until the real deadlock is triggered. > >>> > >>> For example, lockdep report can be triggered in the report[3] with this > >>> patch applied. > >>> > >>> [1] occasional block layer hang when setting 'echo noop > /sys/block/sda/queue/scheduler' > >>> https://bugzilla.kernel.org/show_bug.cgi?id=219166 > >>> > >>> [2] del_gendisk() vs blk_queue_enter() race condition > >>> https://lore.kernel.org/linux-block/20241003085610.GK11458@xxxxxxxxxx/ > >>> > >>> [3] queue_freeze & queue_enter deadlock in scsi > >>> https://lore.kernel.org/linux-block/ZxG38G9BuFdBpBHZ@fedora/T/#u > >>> > >>> Reviewed-by: Christoph Hellwig <hch@xxxxxx> > >>> Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx> > >> This patch landed yesterday in linux-next as commit f1be1788a32e > >> ("block: model freeze & enter queue as lock for supporting lockdep"). > >> In my tests I found that it introduces the following 2 lockdep warnings: > >> > >> > ... > >> > >> > >> 2. On QEMU's ARM64 virt machine, observed during system suspend/resume > >> cycle: > >> > >> # time rtcwake -s10 -mmem > >> rtcwake: wakeup from "mem" using /dev/rtc0 at Tue Oct 29 11:54:30 2024 > >> PM: suspend entry (s2idle) > >> Filesystems sync: 0.004 seconds > >> Freezing user space processes > >> Freezing user space processes completed (elapsed 0.007 seconds) > >> OOM killer disabled. > >> Freezing remaining freezable tasks > >> Freezing remaining freezable tasks completed (elapsed 0.004 seconds) > >> > >> ====================================================== > >> WARNING: possible circular locking dependency detected > >> 6.12.0-rc4+ #9291 Not tainted > >> ------------------------------------------------------ > >> rtcwake/1299 is trying to acquire lock: > >> ffff80008358a7f8 (rtnl_mutex){+.+.}-{3:3}, at: rtnl_lock+0x1c/0x28 > >> > >> but task is already holding lock: > >> ffff000006136d68 (&q->q_usage_counter(io)#5){++++}-{0:0}, at: > >> virtblk_freeze+0x24/0x60 > >> > >> which lock already depends on the new lock. > >> > >> > >> the existing dependency chain (in reverse order) is: > > This one looks a real thing, at least the added lockdep code works as > > expected, also the blk_mq_freeze_queue() use in virtio-blk's ->suspend() > > is questionable. I will take a further look. > > Did you find a way to fix this one? I still observe such warnings in my > tests, even though your lockdep fixes are already merged to -next: > https://lore.kernel.org/all/20241031133723.303835-1-ming.lei@xxxxxxxxxx/ The lockdep fixes in ->next is just for making the added lockdep work correctly, and virtio-blk is another story. It might be fine to annotate it with blk_mq_freeze_queue_no_owner(), but it looks very fragile to call freeze queue in ->suspend(), and the lock is just kept as being grabbed in the whole suspend code path. Can you try the following patch? diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c index 194417abc105..21488740eb15 100644 --- a/drivers/block/virtio_blk.c +++ b/drivers/block/virtio_blk.c @@ -1594,6 +1594,7 @@ static int virtblk_freeze(struct virtio_device *vdev) /* Ensure no requests in virtqueues before deleting vqs. */ blk_mq_freeze_queue(vblk->disk->queue); + blk_mq_unfreeze_queue(vblk->disk->queue); /* Ensure we don't receive any more interrupts */ virtio_reset_device(vdev); @@ -1617,8 +1618,6 @@ static int virtblk_restore(struct virtio_device *vdev) return ret; virtio_device_ready(vdev); - - blk_mq_unfreeze_queue(vblk->disk->queue); return 0; } #endif Thanks, Ming
