block: Make blk_cleanup_queue() wait until request_fn finished
Bart Van Assche [Wed, 28 Nov 2012 12:46:45 +0000 (13:46 +0100)]
Some request_fn implementations, e.g. scsi_request_fn(), unlock
the queue lock internally. This may result in multiple threads
executing request_fn for the same queue simultaneously. Keep
track of the number of active request_fn calls and make sure that
blk_cleanup_queue() waits until all active request_fn invocations
have finished. A block driver may start cleaning up resources
needed by its request_fn as soon as blk_cleanup_queue() finished,
so blk_cleanup_queue() must wait for all outstanding request_fn
invocations to finish.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Reported-by: Chanho Min <chanho.min@lge.com>
Cc: James Bottomley <JBottomley@Parallels.com>
Cc: Mike Christie <michaelc@cs.wisc.edu>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-core.c
include/linux/blkdev.h

index 9fb2353..473015e 100644 (file)
@@ -309,7 +309,16 @@ 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--;
 }
 
 /**
@@ -408,6 +417,7 @@ 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;
 
                /*
                 * Unfortunately, requests are queued at and tracked from
index 8bc46c2..c9d233e 100644 (file)
@@ -378,6 +378,12 @@ 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;
 
        unsigned int            rq_timeout;
        struct timer_list       timeout;