rust nvme driver: potential sleep-in-atomic-context

[Dennis Dai]

The rust nvme driver [1] (which is still pending to be merged into
mainline [2]) has a potential sleep-in-atomic-context bug.

The potential buggy code is below

    // drivers/block/nvme.rs:192
    dev.queues.lock().io.try_reserve(nr_io_queues as _)?;
    // drivers/block/nvme.rs:227
    dev.queues.lock().io.try_push(io_queue.clone())?;

The queues field is wrapped in SpinLock, which means that we cannot
sleep (or indirectly call any function that may sleep) when the lock
is held.
However try_reserve function may indirectly call krealloc with a
sleepable flag GFP_KERNEL (that's default behaviour of the global rust
allocator).
The the case is similar for try_push.

I wonder if the bug could be confirmed.


[1] https://github.com/metaspace/rust-linux/commit/d88c3744d6cbdf11767e08bad56cbfb67c4c96d0
[2] https://lore.kernel.org/lkml/202210010816.1317F2C@keescook/