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Subject: Re: [PATCH] nvme: do not call del_gendisk() on a disk that was never
 added
To:     Niklas Cassel <niklas.cassel@wdc.com>,
        Keith Busch <kbusch@kernel.org>, Jens Axboe <axboe@fb.com>,
        Christoph Hellwig <hch@lst.de>,
        Sagi Grimberg <sagi@grimberg.me>,
        James Smart <james.smart@broadcom.com>,
        Israel Rukshin <israelr@mellanox.com>
Cc:     linux-nvme@lists.infradead.org, linux-kernel@vger.kernel.org
References: <20200607114520.130756-1-niklas.cassel@wdc.com>
From:   Max Gurtovoy <maxg@mellanox.com>
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Date:   Sun, 7 Jun 2020 16:13:39 +0300
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On 6/7/2020 2:45 PM, Niklas Cassel wrote:
> device_add_disk() is negated by del_gendisk().
> alloc_disk_node() is negated by put_disk().
>
> In nvme_alloc_ns(), device_add_disk() is one of the last things being
> called in the success case, and only void functions are being called
> after this. Therefore this call should not be negated in the error path.
>
> The superfluous call to del_gendisk() leads to the following prints:
> [    7.839975] kobject: '(null)' (000000001ff73734): is not initialized, yet kobject_put() is being called.
> [    7.840865] WARNING: CPU: 2 PID: 361 at lib/kobject.c:736 kobject_put+0x70/0x120
>
> Fixes: 33cfdc2aa696 ("nvme: enforce extended LBA format for fabrics metadata")
> Signed-off-by: Niklas Cassel <niklas.cassel@wdc.com>
> ---
> An alternative would be to do like nvme_ns_remove(), i.e. in the error
> path; check if ns->disk->flags & GENHD_FL_UP is set, and only then call
> del_gendisk(). However, that seems unnecessary, since as nvme_alloc_ns()
> is currently written, we know that device_add_disk() does not need to be
> negated.
>
>   drivers/nvme/host/core.c | 4 +---
>   1 file changed, 1 insertion(+), 3 deletions(-)

Looks good,

Reviewed-by: Max Gurtovoy <maxg@mellanox.com>