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: 6e4df4c6 ("nbd: reduce the nbd_index_mutex scope") Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> [hch: split from a larger patch, added comments] Signed-off-by: Christoph Hellwig <hch@lst.de> Link: https://lore.kernel.org/r/20210825163108.50713-4-hch@lst.de Reviewed-by: Josef Bacik <josef@toxicpanda.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
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