MD RAID5: Avoid accessing gendisk or queue structs when not available

MD RAID5:  Fix kernel oops when RAID4/5/6 is used via device-mapper

Commit a9add5d (v3.8-rc1) added blktrace calls to the RAID4/5/6 driver.
However, when device-mapper is used to create RAID4/5/6 arrays, the
mddev->gendisk and mddev->queue fields are not setup.  Therefore, calling
things like trace_block_bio_remap will cause a kernel oops.  This patch
conditionalizes those calls on whether the proper fields exist to make
the calls.  (Device-mapper will call trace_block_bio_remap on its own.)

This patch is suitable for the 3.8.y stable kernel.

Cc: stable@vger.kernel.org (v3.8+)
Signed-off-by: Jonathan Brassow <jbrassow@redhat.com>
Signed-off-by: NeilBrown <neilb@suse.de>

1 files changed, 20 insertions, 13 deletions

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 5601dda1bc40..52ba88a10668 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -674,9 +674,11 @@ static void ops_run_io(struct stripe_head *sh, struct stripe_head_state *s)
                         bi->bi_next = NULL;
                         if (rrdev)
                                 set_bit(R5_DOUBLE_LOCKED, &sh->dev[i].flags);
-                        trace_block_bio_remap(bdev_get_queue(bi->bi_bdev),
-                                              bi, disk_devt(conf->mddev->gendisk),
-                                              sh->dev[i].sector);
+
+                        if (conf->mddev->gendisk)
+                                trace_block_bio_remap(bdev_get_queue(bi->bi_bdev),
+                                                      bi, disk_devt(conf->mddev->gendisk),
+                                                      sh->dev[i].sector);
                         generic_make_request(bi);
                 }
                 if (rrdev) {
@@ -704,9 +706,10 @@ static void ops_run_io(struct stripe_head *sh, struct stripe_head_state *s)
                         rbi->bi_io_vec[0].bv_offset = 0;
                         rbi->bi_size = STRIPE_SIZE;
                         rbi->bi_next = NULL;
-                        trace_block_bio_remap(bdev_get_queue(rbi->bi_bdev),
-                                              rbi, disk_devt(conf->mddev->gendisk),
-                                              sh->dev[i].sector);
+                        if (conf->mddev->gendisk)
+                                trace_block_bio_remap(bdev_get_queue(rbi->bi_bdev),
+                                                      rbi, disk_devt(conf->mddev->gendisk),
+                                                      sh->dev[i].sector);
                         generic_make_request(rbi);
                 }
                 if (!rdev && !rrdev) {
@@ -2835,8 +2838,10 @@ static void handle_stripe_dirtying(struct r5conf *conf,
         set_bit(STRIPE_HANDLE, &sh->state);
         if (rmw < rcw && rmw > 0) {
                 /* prefer read-modify-write, but need to get some data */
-                blk_add_trace_msg(conf->mddev->queue, "raid5 rmw %llu %d",
-                                  (unsigned long long)sh->sector, rmw);
+                if (conf->mddev->queue)
+                        blk_add_trace_msg(conf->mddev->queue,
+                                          "raid5 rmw %llu %d",
+                                          (unsigned long long)sh->sector, rmw);
                 for (i = disks; i--; ) {
                         struct r5dev *dev = &sh->dev[i];
                         if ((dev->towrite || i == sh->pd_idx) &&
@@ -2886,7 +2891,7 @@ static void handle_stripe_dirtying(struct r5conf *conf,
                                 }
                         }
                 }
-                if (rcw)
+                if (rcw && conf->mddev->queue)
                         blk_add_trace_msg(conf->mddev->queue, "raid5 rcw %llu %d %d %d",
                                           (unsigned long long)sh->sector,
                                           rcw, qread, test_bit(STRIPE_DELAYED, &sh->state));
@@ -3993,9 +3998,10 @@ static int chunk_aligned_read(struct mddev *mddev, struct bio * raid_bio)
                 atomic_inc(&conf->active_aligned_reads);
                 spin_unlock_irq(&conf->device_lock);
 
-                trace_block_bio_remap(bdev_get_queue(align_bi->bi_bdev),
-                                      align_bi, disk_devt(mddev->gendisk),
-                                      raid_bio->bi_sector);
+                if (mddev->gendisk)
+                        trace_block_bio_remap(bdev_get_queue(align_bi->bi_bdev),
+                                              align_bi, disk_devt(mddev->gendisk),
+                                              raid_bio->bi_sector);
                 generic_make_request(align_bi);
                 return 1;
         } else {
@@ -4089,7 +4095,8 @@ static void raid5_unplug(struct blk_plug_cb *blk_cb, bool from_schedule)
                 }
                 spin_unlock_irq(&conf->device_lock);
         }
-        trace_block_unplug(mddev->queue, cnt, !from_schedule);
+        if (mddev->queue)
+                trace_block_unplug(mddev->queue, cnt, !from_schedule);
         kfree(cb);
 }