[dm-devel] v4.8 dm-mpath

[Bart Van Assche]

Hello Mike,

If I trigger failover and failback with kernel v4.8-rc2 and ib_srp then I
see the following:

BUG: unable to handle kernel NULL pointer dereference at 0000000000000080
IP: [<ffffffff8130d03b>] blk_mq_insert_request+0x3b/0xc0
CPU: 4 PID: 12606 Comm: kdmwork-254:1 Not tainted 4.8.0-rc2-dbg+ #1
Hardware name: Dell Inc. PowerEdge R430/03XKDV, BIOS 1.0.2 11/17/2014
task: ffff880363d3e240 task.stack: ffff8803618ac000
RIP: 0010:[<ffffffff8130d03b>]  [<ffffffff8130d03b>] blk_mq_insert_request+0x3b/0xc0
Call Trace:
 [<ffffffff81300da9>] blk_insert_cloned_request+0xa9/0x1e0
 [<ffffffffa04302f0>] map_request+0x190/0x2d0 [dm_mod]
 [<ffffffffa043044d>] map_tio_request+0x1d/0x40 [dm_mod]
 [<ffffffff81087101>] kthread_worker_fn+0xd1/0x1b0
 [<ffffffff81086fba>] kthread+0xea/0x100
 [<ffffffff8162d53f>] ret_from_fork+0x1f/0x40

(gdb) list *(blk_mq_insert_request+0x3b)
0xffffffff8130d03b is in blk_mq_insert_request (block/blk-mq.c:1078).
1073            struct request_queue *q = rq->q;
1074            struct blk_mq_hw_ctx *hctx;
1075            struct blk_mq_ctx *ctx = rq->mq_ctx, *current_ctx;
1076
1077            current_ctx = blk_mq_get_ctx(q);
1078            if (!cpu_online(ctx->cpu))
1079                    rq->mq_ctx = ctx = current_ctx;
1080
1081            hctx = q->mq_ops->map_queue(q, ctx->cpu);
1082
(gdb) print &((struct blk_mq_ctx*)0)->cpu
$1 = (unsigned int *) 0x80

I think this means that ctx->cpu == NULL was hit.

This was observed with the same test software and configuration I
used for my kernel v4.7 tests (CONFIG_SCSI_MQ_DEFAULT=y and
CONFIG_DM_MQ_DEFAULT=n).

The above callstack was not observed while testing kernel v4.7.

Can you have a look at this?

Thanks,

Bart.