On 01/17/2017 04:47 AM, Jens Axboe wrote:

On 01/17/2017 12:57 AM, Hannes Reinecke wrote:

quoted

Hi Jens,

I gave your latest patchset from

git.kernel.dk/linux-block blk-mq-sched

I see a kernel oops when shutting down:

[ 2132.708929] systemd-shutdown[1]: Detaching DM devices.
[ 2132.965107] BUG: unable to handle kernel NULL pointer dereference at
00000000
00000001
[ 2133.037182] IP: dd_merged_requests+0x6/0x60
[ 2133.077816] PGD 0
[ 2133.077818]
[ 2133.113087] Oops: 0000 [#1] SMP
[ list of modules removed ]
[ 2133.925265] CPU: 20 PID: 1 Comm: systemd-shutdow Not tainted
4.10.0-rc4+ #543
[ 2133.990034] Hardware name: HP ProLiant DL380p Gen8, BIOS P70 09/18/2013
[ 2134.050522] task: ffff88042d614040 task.stack: ffffc90003150000
[ 2134.106915] RIP: 0010:dd_merged_requests+0x6/0x60
[ 2134.150593] RSP: 0018:ffffc90003153b18 EFLAGS: 00010002
[ 2134.198740] RAX: ffffffff81cc6de0 RBX: ffff8804296d5040 RCX:
0000000000000001
[ 2134.262708] RDX: 0000000000000001 RSI: 0000000000000001 RDI:
ffff8804296d5040
[ 2134.326987] RBP: ffffc90003153b30 R08: 0000000000000000 R09:
0000000000000000
[ 2134.391054] R10: 0000000000000000 R11: 0001f8180001f815 R12:
0000000000000000
[ 2134.456095] R13: ffff8804296d5040 R14: ffff8804099801f0 R15:
0000000000000004
[ 2134.521196] FS:  00007fd64d3bf840(0000) GS:ffff88042f900000(0000)
knlGS:0000000000000000
[ 2134.595178] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 2134.648637] CR2: 0000000000000001 CR3: 000000081b892000 CR4:
00000000000406e0
[ 2134.713349] Call Trace:
[ 2134.737168]  ? elv_drain_elevator+0x29/0xa0
[ 2134.775821]  __blk_drain_queue+0x52/0x1a0
[ 2134.812473]  blk_queue_bypass_start+0x6e/0xa0
[ 2134.854009]  blkcg_deactivate_policy+0x30/0xf0
[ 2134.894993]  blk_throtl_exit+0x34/0x50
[ 2134.929450]  blkcg_exit_queue+0x35/0x40
[ 2134.965089]  blk_release_queue+0x33/0xe0
[ 2135.001364]  kobject_cleanup+0x63/0x170
[ 2135.037412]  kobject_put+0x25/0x50
[ 2135.068622]  blk_cleanup_queue+0x198/0x260
[ 2135.107780]  cleanup_mapped_device+0xb5/0xf0 [dm_mod]
[ 2135.154741]  __dm_destroy+0x1a5/0x290 [dm_mod]
[ 2135.195009]  dm_destroy+0x13/0x20 [dm_mod]
[ 2135.232149]  dev_remove+0xde/0x120 [dm_mod]
[ 2135.270184]  ? dev_suspend+0x210/0x210 [dm_mod]
[ 2135.311478]  ctl_ioctl+0x20b/0x510 [dm_mod]
[ 2135.349680]  ? terminate_walk+0xc3/0x140
[ 2135.385442]  ? kmem_cache_free+0x10/0x260
[ 2135.422315]  dm_ctl_ioctl+0x13/0x20 [dm_mod]

Known issue?

Try with this, looks like we're calling the old bypass path for the new
path, which is now triggering because q->elevator is true.

Should have grepped, there's one more path that uses the old bypass
path for q->mq_ops, potentially. This one handles that one, too.

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 8ba0af780e88..2630f64bed19 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c

@@ -1223,7 +1223,11 @@ int blkcg_activate_policy(struct request_queue *q,
 	if (blkcg_policy_enabled(q, pol))
 		return 0;
 
-	blk_queue_bypass_start(q);
+	if (q->mq_ops) {
+		blk_mq_freeze_queue(q);
+		blk_mq_quiesce_queue(q);
+	} else
+		blk_queue_bypass_start(q);
 pd_prealloc:
 	if (!pd_prealloc) {
 		pd_prealloc = pol->pd_alloc_fn(GFP_KERNEL, q->node);

@@ -1261,7 +1265,10 @@ int blkcg_activate_policy(struct request_queue *q,
 
 	spin_unlock_irq(q->queue_lock);
 out_bypass_end:
-	blk_queue_bypass_end(q);
+	if (q->mq_ops)
+		blk_mq_unfreeze_queue(q);
+	else
+		blk_queue_bypass_end(q);
 	if (pd_prealloc)
 		pol->pd_free_fn(pd_prealloc);
 	return ret;

@@ -1284,7 +1291,12 @@ void blkcg_deactivate_policy(struct request_queue *q,
 	if (!blkcg_policy_enabled(q, pol))
 		return;
 
-	blk_queue_bypass_start(q);
+	if (q->mq_ops) {
+		blk_mq_freeze_queue(q);
+		blk_mq_quiesce_queue(q);
+	} else
+		blk_queue_bypass_start(q);
+
 	spin_lock_irq(q->queue_lock);
 
 	__clear_bit(pol->plid, q->blkcg_pols);

@@ -1304,7 +1316,11 @@ void blkcg_deactivate_policy(struct request_queue *q,
 	}
 
 	spin_unlock_irq(q->queue_lock);
-	blk_queue_bypass_end(q);
+
+	if (q->mq_ops)
+		blk_mq_unfreeze_queue(q);
+	else
+		blk_queue_bypass_end(q);
 }
 EXPORT_SYMBOL_GPL(blkcg_deactivate_policy);
 

diff --git a/block/elevator.c b/block/elevator.c
index d14cb87e6564..464372840774 100644
--- a/block/elevator.c
+++ b/block/elevator.c

@@ -613,6 +613,9 @@ void elv_drain_elevator(struct request_queue *q)
 {
 	static int printed;
 
+	if (WARN_ON_ONCE(q->mq_ops))
+		return;
+
 	lockdep_assert_held(q->queue_lock);
 
 	while (q->elevator->type->ops.sq.elevator_dispatch_fn(q, 1))

-- 
Jens Axboe