On Tue, Mar 14, 2023 at 11:21:54AM -0700, Bart Van Assche wrote:
> do_req_filebacked() calls blk_mq_complete_request() synchronously or
> asynchronously when using asynchronous I/O unless memory allocation fails.
> Hence, modify loop_handle_cmd() such that it does not dereference 'cmd' nor
> 'rq' after do_req_filebacked() finished unless we are sure that the request
> has not yet been completed. This patch fixes the following kernel crash:
>
> Unable to handle kernel NULL pointer dereference at virtual address 0000000000000054
> Call trace:
> css_put.42938+0x1c/0x1ac
> loop_process_work+0xc8c/0xfd4
> loop_rootcg_workfn+0x24/0x34
> process_one_work+0x244/0x558
> worker_thread+0x400/0x8fc
> kthread+0x16c/0x1e0
> ret_from_fork+0x10/0x20
>
> Cc: Christoph Hellwig <hch@xxxxxx>
> Cc: Ming Lei <ming.lei@xxxxxxxxxx>
> Cc: Jan Kara <jack@xxxxxxx>
> Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
> Cc: Dan Schatzberg <schatzberg.dan@xxxxxxxxx>
> Fixes: c74d40e8b5e2 ("loop: charge i/o to mem and blk cg")
> Fixes: bc07c10a3603 ("block: loop: support DIO & AIO")
> Signed-off-by: Bart Van Assche <bvanassche@xxxxxxx>
Reviewed-by: Ming Lei <ming.lei@xxxxxxxxxx>
Thanks,
Ming
