Re: [PATCH] nvmet: fix race in nvmet_bio_done() leading to NULL pointer dereference

[Keith Busch <kbusch@kernel.org>]

On Wed, Jan 21, 2026 at 05:38:54PM +0800, Ming Lei wrote:
> There is a race condition in nvmet_bio_done() that can cause a NULL
> pointer dereference in blk_cgroup_bio_start():
> 
> 1. nvmet_bio_done() is called when a bio completes
> 2. nvmet_req_complete() is called, which invokes req->ops->queue_response(req)
> 3. The queue_response callback can re-queue and re-submit the same request
> 4. The re-submission reuses the same inline_bio from nvmet_req
> 5. Meanwhile, nvmet_req_bio_put() (called after nvmet_req_complete)
>    invokes bio_uninit() for inline_bio, which sets bio->bi_blkg to NULL
> 6. The re-submitted bio enters submit_bio_noacct_nocheck()
> 7. blk_cgroup_bio_start() dereferences bio->bi_blkg, causing a crash:
> 
>   BUG: kernel NULL pointer dereference, address: 0000000000000028
>   #PF: supervisor read access in kernel mode
>   RIP: 0010:blk_cgroup_bio_start+0x10/0xd0
>   Call Trace:
>    submit_bio_noacct_nocheck+0x44/0x250
>    nvmet_bdev_execute_rw+0x254/0x370 [nvmet]
>    process_one_work+0x193/0x3c0
>    worker_thread+0x281/0x3a0
> 
> Fix this by reordering nvmet_bio_done() to call nvmet_req_bio_put()
> BEFORE nvmet_req_complete(). This ensures the bio is cleaned up before
> the request can be re-submitted, preventing the race condition.

Thanks, applied to nvme-6.19.