From 7ff54fed20c1b30564e817aaf70f64cb92c30c5c Mon Sep 17 00:00:00 2001 From: Mike Christie Date: Sun, 8 Dec 2019 16:51:50 -0600 Subject: [PATCH] nbd: fix shutdown and recv work deadlock v2 This fixes a regression added with: commit 0f7abac3d7496187c0db4e34dbbc29d04cf15786 Author: Mike Christie Date: Sun Aug 4 14:10:06 2019 -0500 nbd: fix max number of supported devs where we can deadlock during device shutdown. The problem occurs if the recv_work's nbd_config_put occurs after nbd_start_device_ioctl has returned and the userspace app has droppped its reference via closing the device and running nbd_release. The recv_work nbd_config_put call would then drop the refcount to zero and try to destroy the config which would try to do destroy_workqueue from the recv work. This patch just has nbd_start_device_ioctl do a flush_workqueue when it wakes so we know after the ioctl returns running works have exited. This also fixes a possible race where we could try to reuse the device while old recv_works are still running. Cc: stable@vger.kernel.org Fixes: 0f7abac3d749 ("nbd: fix max number of supported devs") Signed-off-by: Mike Christie Signed-off-by: Jens Axboe --- drivers/block/nbd.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c index 57532465fb83a..b4607dd961852 100644 --- a/drivers/block/nbd.c +++ b/drivers/block/nbd.c @@ -1296,10 +1296,10 @@ static int nbd_start_device_ioctl(struct nbd_device *nbd, struct block_device *b mutex_unlock(&nbd->config_lock); ret = wait_event_interruptible(config->recv_wq, atomic_read(&config->recv_threads) == 0); - if (ret) { + if (ret) sock_shutdown(nbd); - flush_workqueue(nbd->recv_workq); - } + flush_workqueue(nbd->recv_workq); + mutex_lock(&nbd->config_lock); nbd_bdev_reset(bdev); /* user requested, ignore socket errors */ -- 2.39.5