From: Tetsuo Handa Date: Wed, 25 Aug 2021 16:31:05 +0000 (+0200) Subject: nbd: prevent IDR lookups from finding partially initialized devices X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=75b7f62aa65d5c496391ec2c3db3561aaf81a403;p=linux.git nbd: prevent IDR lookups from finding partially initialized devices Previously nbd_index_mutex was held during whole add/remove/lookup operations in order to guarantee that partially initialized devices are not reachable via idr_find() or idr_for_each(). But now that partially initialized devices become reachable as soon as idr_alloc() succeeds, we need to skip partially initialized devices. Since it seems that all functions use refcount_inc_not_zero(&nbd->refs) in order to skip destroying devices, update nbd->refs from zero to non-zero as the last step of device initialization in order to also skip partially initialized devices. Fixes: 6e4df4c64881 ("nbd: reduce the nbd_index_mutex scope") Signed-off-by: Tetsuo Handa [hch: split from a larger patch, added comments] Signed-off-by: Christoph Hellwig Link: https://lore.kernel.org/r/20210825163108.50713-4-hch@lst.de Reviewed-by: Josef Bacik Signed-off-by: Jens Axboe --- diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c index 938ca7f5a11fb..b1ed2360ef323 100644 --- a/drivers/block/nbd.c +++ b/drivers/block/nbd.c @@ -1747,7 +1747,11 @@ static struct nbd_device *nbd_dev_add(int index, unsigned int refs) mutex_init(&nbd->config_lock); refcount_set(&nbd->config_refs, 0); - refcount_set(&nbd->refs, refs); + /* + * Start out with a zero references to keep other threads from using + * this device until it is fully initialized. + */ + refcount_set(&nbd->refs, 0); INIT_LIST_HEAD(&nbd->list); disk->major = NBD_MAJOR; @@ -1766,6 +1770,11 @@ static struct nbd_device *nbd_dev_add(int index, unsigned int refs) disk->private_data = nbd; sprintf(disk->disk_name, "nbd%d", index); add_disk(disk); + + /* + * Now publish the device. + */ + refcount_set(&nbd->refs, refs); nbd_total_devices++; return nbd;