blk: Fix lock inversion between ioc lock and bfqd lock
Lockdep complains about lock inversion between ioc->lock and bfqd->lock:
bfqd -> ioc:
put_io_context+0x33/0x90 -> ioc->lock grabbed
blk_mq_free_request+0x51/0x140
blk_put_request+0xe/0x10
blk_attempt_req_merge+0x1d/0x30
elv_attempt_insert_merge+0x56/0xa0
blk_mq_sched_try_insert_merge+0x4b/0x60
bfq_insert_requests+0x9e/0x18c0 -> bfqd->lock grabbed
blk_mq_sched_insert_requests+0xd6/0x2b0
blk_mq_flush_plug_list+0x154/0x280
blk_finish_plug+0x40/0x60
ext4_writepages+0x696/0x1320
do_writepages+0x1c/0x80
__filemap_fdatawrite_range+0xd7/0x120
sync_file_range+0xac/0xf0
ioc->bfqd:
bfq_exit_icq+0xa3/0xe0 -> bfqd->lock grabbed
put_io_context_active+0x78/0xb0 -> ioc->lock grabbed
exit_io_context+0x48/0x50
do_exit+0x7e9/0xdd0
do_group_exit+0x54/0xc0
To avoid this inversion we change blk_mq_sched_try_insert_merge() to not
free the merged request but rather leave that upto the caller similarly
to blk_mq_sched_try_merge(). And in bfq_insert_requests() we make sure
to free all the merged requests after dropping bfqd->lock.
Fixes: aee69d78dec0 ("block, bfq: introduce the BFQ-v0 I/O scheduler as an extra scheduler")
Reviewed-by: Ming Lei <[email protected]>
Acked-by: Paolo Valente <[email protected]>
Signed-off-by: Jan Kara <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jens Axboe <[email protected]>
diff --git a/block/mq-deadline-main.c b/block/mq-deadline-main.c
index 4815e53..9db6da9 100644
--- a/block/mq-deadline-main.c
+++ b/block/mq-deadline-main.c
@@ -719,6 +719,7 @@ static void dd_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq,
struct dd_per_prio *per_prio;
enum dd_prio prio;
struct dd_blkcg *blkcg;
+ LIST_HEAD(free);
lockdep_assert_held(&dd->lock);
@@ -742,8 +743,10 @@ static void dd_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq,
WARN_ON_ONCE(rq->elv.priv[0]);
rq->elv.priv[0] = blkcg;
- if (blk_mq_sched_try_insert_merge(q, rq))
+ if (blk_mq_sched_try_insert_merge(q, rq, &free)) {
+ blk_mq_free_requests(&free);
return;
+ }
trace_block_rq_insert(rq);
