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nbd: prevent IDR lookups from finding partially initialized devices

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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: 6e4df4c648 ("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>
This commit is contained in:
Tetsuo Handa 2021-08-25 18:31:05 +02:00 committed by Jens Axboe
parent 409e0ff10e
commit 75b7f62aa6
1 changed files with 10 additions and 1 deletions
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11
drivers/block/nbd.c
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@ -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;