Some block drivers, e.g. dm and SCSI, need to trigger a queue run from inside functions that may be invoked by their request_fn() implementation. Make sure that invoking blk_run_queue() instead of blk_run_queue_async() from such functions does not trigger recursion.
Signed-off-by: Bart Van Assche <[email protected]> Cc: Jens Axboe <[email protected]> Cc: Tejun Heo <[email protected]> Cc: James Bottomley <[email protected]> Cc: Alasdair G Kergon <[email protected]> Cc: Mike Snitzer <[email protected]> Cc: Jun'ichi Nomura <[email protected]> --- block/blk-core.c | 34 +++++++++++++++++++++++----------- include/linux/blkdev.h | 8 ++------ 2 files changed, 25 insertions(+), 17 deletions(-) diff --git a/block/blk-core.c b/block/blk-core.c index c973249..ac4f310 100644 --- a/block/blk-core.c +++ b/block/blk-core.c @@ -304,22 +304,34 @@ EXPORT_SYMBOL(blk_sync_queue); * This variant runs the queue whether or not the queue has been * stopped. Must be called with the queue lock held and interrupts * disabled. See also @blk_run_queue. + * + * Notes: + * It is allowed to invoke __blk_run_queue() or blk_run_queue() (whichever + * is appropriate) from inside a request_fn() implementation. Such + * recursive calls are converted into iteration with the help of the + * needs_rerun flag. + * + * Some request_fn() implementations, e.g. scsi_request_fn() and + * dm_request_fn(), unlock the queue lock internally. For such + * implementations the request_fn_running check does not only prevent + * recursion but also avoids that multiple threads execute such a + * request_fn() implementation concurrently. */ inline void __blk_run_queue_uncond(struct request_queue *q) { if (unlikely(blk_queue_dead(q))) return; - /* - * Some request_fn implementations, e.g. scsi_request_fn(), unlock - * the queue lock internally. As a result multiple threads may be - * running such a request function concurrently. Keep track of the - * number of active request_fn invocations such that blk_drain_queue() - * can wait until all these request_fn calls have finished. - */ - q->request_fn_active++; - q->request_fn(q); - q->request_fn_active--; + if (!q->request_fn_running) { + do { + q->needs_rerun = false; + q->request_fn_running = true; + q->request_fn(q); + q->request_fn_running = false; + } while (q->needs_rerun); + } else { + q->needs_rerun = true; + } } /** @@ -418,7 +430,7 @@ static void __blk_drain_queue(struct request_queue *q, bool drain_all) __blk_run_queue(q); drain |= q->nr_rqs_elvpriv; - drain |= q->request_fn_active; + drain |= q->request_fn_running; /* * Unfortunately, requests are queued at and tracked from diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h index f94bc83..20da3c8 100644 --- a/include/linux/blkdev.h +++ b/include/linux/blkdev.h @@ -378,12 +378,8 @@ struct request_queue { unsigned int nr_sorted; unsigned int in_flight[2]; - /* - * Number of active block driver functions for which blk_drain_queue() - * must wait. Must be incremented around functions that unlock the - * queue_lock internally, e.g. scsi_request_fn(). - */ - unsigned int request_fn_active; + bool request_fn_running; + bool needs_rerun; unsigned int rq_timeout; struct timer_list timeout; -- 1.7.10.4 -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
