From: Krystian Kaniewski Commit 242a49e5c878 ("nbd: freeze the queue for queue limits updates") correctly added queue freezing for live updates of real queue limits. However, nbd_set_size() is also used for capacity-only generic netlink updates, so the freeze is unnecessarily broad for the reported request. When an NBD server becomes unresponsive, it leaves I/O in flight. An unnecessary queue freeze during a size-only reconfigure will wait forever for these in-flight I/Os to complete while the global genl_mutex is held, leading to a global generic netlink stall. A size-only reconfigure can update config->bytesize and disk capacity directly because the effective block size and all other queue limits stay unchanged. This patch introduces nbd_size_set() to handle size-only updates directly without freezing the queue or committing queue limits. Capacity-only generic netlink reconfiguration no longer freezes the queue, while startup and real block-size changes continue to use the existing frozen limits update via nbd_set_size(). Fixes: 242a49e5c878 ("nbd: freeze the queue for queue limits updates") Assisted-by: Gemini:gemini-3.5-flash Gemini:gemini-3.1-pro-preview syzbot Reported-by: syzbot Closes: https://syzkaller.appspot.com/bug?extid=f272bbfbf8498ddadea5 Link: https://syzkaller.appspot.com/ai_job?id=786b3bd0-fdad-4252-9e86-7a6a35c3b756 Signed-off-by: Krystian Kaniewski --- diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c index fe63f3c55..567b031ec 100644 --- a/drivers/block/nbd.c +++ b/drivers/block/nbd.c @@ -331,6 +331,27 @@ static void nbd_mark_nsock_dead(struct nbd_device *nbd, struct nbd_sock *nsock, nsock->sent = 0; } +static void nbd_size_update(struct nbd_device *nbd) +{ + struct nbd_config *config = nbd->config; + + if (max_part) + set_bit(GD_NEED_PART_SCAN, &nbd->disk->state); + if (!set_capacity_and_notify(nbd->disk, config->bytesize >> 9)) + kobject_uevent(&nbd_to_dev(nbd)->kobj, KOBJ_CHANGE); +} + +static int nbd_size_set(struct nbd_device *nbd, loff_t bytesize) +{ + if (bytesize < 0) + return -EINVAL; + + nbd->config->bytesize = bytesize; + if (nbd->pid) + nbd_size_update(nbd); + return 0; +} + static int nbd_set_size(struct nbd_device *nbd, loff_t bytesize, loff_t blksize) { struct queue_limits lim; @@ -375,10 +396,7 @@ static int nbd_set_size(struct nbd_device *nbd, loff_t bytesize, loff_t blksize) if (error) return error; - if (max_part) - set_bit(GD_NEED_PART_SCAN, &nbd->disk->state); - if (!set_capacity_and_notify(nbd->disk, bytesize >> 9)) - kobject_uevent(&nbd_to_dev(nbd)->kobj, KOBJ_CHANGE); + nbd_size_update(nbd); return 0; } @@ -2062,11 +2080,19 @@ static int nbd_genl_size_set(struct genl_info *info, struct nbd_device *nbd) if (info->attrs[NBD_ATTR_SIZE_BYTES]) bytes = nla_get_u64(info->attrs[NBD_ATTR_SIZE_BYTES]); - if (info->attrs[NBD_ATTR_BLOCK_SIZE_BYTES]) + if (info->attrs[NBD_ATTR_BLOCK_SIZE_BYTES]) { bsize = nla_get_u64(info->attrs[NBD_ATTR_BLOCK_SIZE_BYTES]); + if (!bsize) + bsize = 1u << NBD_DEF_BLKSIZE_BITS; + if (blk_validate_block_size(bsize)) + return -EINVAL; + } - if (bytes != config->bytesize || bsize != nbd_blksize(config)) - return nbd_set_size(nbd, bytes, bsize); + if (bytes != config->bytesize || bsize != nbd_blksize(config)) { + if (bsize != nbd_blksize(config)) + return nbd_set_size(nbd, bytes, bsize); + return nbd_size_set(nbd, bytes); + } return 0; } base-commit: 8cd9520d35a6c38db6567e97dd93b1f11f185dc6 -- See https://goo.gle/syzbot-ai-patches for information about AI-generated patches. You can comment on the patch as usual, syzbot will try to address the comments and send a new version of the patch if necessary. syzbot engineers can be reached at syzkaller@googlegroups.com.