[dm-devel] blk-mq request allocation stalls

[Bart Van Assche]

On 01/12/15 16:42, Jens Axboe wrote:
> On 01/12/2015 07:46 AM, Bart Van Assche wrote:
>> bt_get: __bt_get() returned -1
>> queue_num=2, nr_tags=62, reserved_tags=0, bits_per_word=3
>> nr_free=62, nr_reserved=0, may_queue=0
>> active_queues=8
> 
> Can you add dumping of hctx->nr_active when this fails? You case is that 
> the may_queue logic says no-can-do, so it smells like the nr_active 
> accounting is wonky since you have supposedly no allocated tags, yet it 
> clearly thinks that you do.

Hello Jens,

The requested output is as follows:

bt_get: __bt_get() returned -1
queue_num=0, nr_tags=62, reserved_tags=0, bits_per_word=3
nr_free=62, nr_reserved=0, hctx->tags->active_queues=7,
hctx->nr_active=9, hctx_may_queue()=0
active_queues=7
CPU: 0 PID: 3111 Comm: kdmwork-253:6 Tainted: G        W
3.19.0-rc4-debug+ #1
Call Trace:
 [<ffffffff814d2763>] dump_stack+0x4c/0x65
 [<ffffffff81259dc7>] bt_get+0x97/0x1e0
 [<ffffffff8125a0af>] blk_mq_get_tag+0x9f/0xd0
 [<ffffffff8125522b>] __blk_mq_alloc_request+0x1b/0x210
 [<ffffffff81256a30>] blk_mq_alloc_request+0xa0/0x150
 [<ffffffff8124ba9e>] blk_get_request+0x2e/0xe0
 [<ffffffffa07d9d0f>] __multipath_map.isra.15+0x1cf/0x210 [dm_multipath]
 [<ffffffffa07d9d6a>] multipath_clone_and_map+0x1a/0x20 [dm_multipath]
 [<ffffffffa0350bb5>] map_tio_request+0x1d5/0x3a0 [dm_mod]
 [<ffffffff81075d16>] kthread_worker_fn+0x86/0x1b0
 [<ffffffff81075c0f>] kthread+0xef/0x110
 [<ffffffff814db4ec>] ret_from_fork+0x7c/0xb0

Bart.