From: Bart Van Assche bvanassche@acm.org
[ Upstream commit 9b0cb770f5d7b1ff40bea7ca385438ee94570eec ]
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@lst.de Cc: Ming Lei ming.lei@redhat.com Cc: Jan Kara jack@suse.cz Cc: Johannes Weiner hannes@cmpxchg.org Cc: Dan Schatzberg schatzberg.dan@gmail.com 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@acm.org Reviewed-by: Ming Lei ming.lei@redhat.com Link: https://lore.kernel.org/r/20230314182155.80625-1-bvanassche@acm.org Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/block/loop.c | 25 +++++++++++++++++-------- 1 file changed, 17 insertions(+), 8 deletions(-)
diff --git a/drivers/block/loop.c b/drivers/block/loop.c index 1b35cbd029c7c..eabbc3bdec221 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -1853,35 +1853,44 @@ static blk_status_t loop_queue_rq(struct blk_mq_hw_ctx *hctx,
static void loop_handle_cmd(struct loop_cmd *cmd) { + struct cgroup_subsys_state *cmd_blkcg_css = cmd->blkcg_css; + struct cgroup_subsys_state *cmd_memcg_css = cmd->memcg_css; struct request *rq = blk_mq_rq_from_pdu(cmd); const bool write = op_is_write(req_op(rq)); struct loop_device *lo = rq->q->queuedata; int ret = 0; struct mem_cgroup *old_memcg = NULL; + const bool use_aio = cmd->use_aio;
if (write && (lo->lo_flags & LO_FLAGS_READ_ONLY)) { ret = -EIO; goto failed; }
- if (cmd->blkcg_css) - kthread_associate_blkcg(cmd->blkcg_css); - if (cmd->memcg_css) + if (cmd_blkcg_css) + kthread_associate_blkcg(cmd_blkcg_css); + if (cmd_memcg_css) old_memcg = set_active_memcg( - mem_cgroup_from_css(cmd->memcg_css)); + mem_cgroup_from_css(cmd_memcg_css));
+ /* + * do_req_filebacked() may call blk_mq_complete_request() synchronously + * or asynchronously if using aio. Hence, do not touch 'cmd' after + * do_req_filebacked() has returned unless we are sure that 'cmd' has + * not yet been completed. + */ ret = do_req_filebacked(lo, rq);
- if (cmd->blkcg_css) + if (cmd_blkcg_css) kthread_associate_blkcg(NULL);
- if (cmd->memcg_css) { + if (cmd_memcg_css) { set_active_memcg(old_memcg); - css_put(cmd->memcg_css); + css_put(cmd_memcg_css); } failed: /* complete non-aio request */ - if (!cmd->use_aio || ret) { + if (!use_aio || ret) { if (ret == -EOPNOTSUPP) cmd->ret = ret; else