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>
---
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 839373451c2b..28eb59fd71ca 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -1859,35 +1859,44 @@ 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
