On 01/11/2017 10:39 PM, Jens Axboe wrote:

Another year, another posting of this patchset. The previous posting
was here:

https://www.spinics.net/lists/kernel/msg2406106.html

(yes, I've skipped v5, it was fixes on top of v4, not the rework).

I've reworked bits of this to get rid of the shadow requests, thanks
to Bart for the inspiration. The missing piece, for me, was the fact
that we have the tags->rqs[] indirection array already. I've done this
somewhat differently, though, by having the internal scheduler tag
map be allocated/torn down when an IO scheduler is attached or
detached. This also means that when we run without a scheduler, we
don't have to do double tag allocations, it'll work like before.

The patchset applies on top of 4.10-rc3, or can be pulled here:

git://git.kernel.dk/linux-block blk-mq-sched.6

Fun continues:

[   28.976708] ata3.00: configured for UDMA/100
[   28.987625] BUG: unable to handle kernel NULL pointer dereference at
0000000000000048
[   28.987632] IP: deadline_add_request+0x15/0x70
[   28.987633] PGD 0
[   28.987634]
[   28.987636] Oops: 0000 [#1] SMP
[   28.987638] Modules linked in: ahci libahci libata uhci_hcd(+)
mgag200(+) i2c_algo_bit drm_kms_helper syscopyarea sysfillrect sysimgblt
fb_sys_fops ttm drm tg3 libphy ehci_pci ehci_hcd usbcore usb_common
ixgbe mdio hpsa(+) dca ptp pps_core scsi_transport_sas fjes(+) sg
dm_multipath dm_mod scsi_dh_rdac scsi_dh_emc scsi_dh_alua autofs4
[   28.987654] CPU: 0 PID: 268 Comm: kworker/u2:2 Not tainted
4.10.0-rc3+ #535
[   28.987655] Hardware name: HP ProLiant ML350p Gen8, BIOS P72 09/08/2013
[   28.987660] Workqueue: events_unbound async_run_entry_fn
[   28.987661] task: ffff880029391600 task.stack: ffffc9000038c000
[   28.987663] RIP: 0010:deadline_add_request+0x15/0x70
[   28.987664] RSP: 0018:ffffc9000038fb00 EFLAGS: 00010286
[   28.987665] RAX: ffff88003260c400 RBX: 0000000000000000 RCX:
0000000000000000
[   28.987666] RDX: ffffc9000038fb68 RSI: 0000000000000000 RDI:
ffff8800293b9040
[   28.987666] RBP: ffffc9000038fb18 R08: 000000000087668] R13:
ffff88003260c400 R14: 0000000000000000 R15: 0000000000000000
[   28.987670] FS:  0000000000000000(0000) GS:ffff880035c00000(0000)
knlGS:0000000000000000
[   28.987670] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   28.987671] CR2: 0000000000000048 CR3: 0000000032b64000 CR4:
00000000000406f0
[   28.987672] Call Trace:
[   28.987677]  blk_mq_sched_get_request+0x12e/0x310
[   28.987678]  ? blk_mq_sched_get_request+0x5/0x310
[   28.987681]  blk_mq_alloc_request+0x40/0x90
[   28.987684]  blk_get_request+0x35/0x110
[   28.987689]  __scsi_execute.isra.24+0x3c/0x160
[   28.987691]  scsi_execute_req_flags+0x94/0x100
[   28.987694]  scsi_probe_and_add_lun+0x207/0xd60
[   28.987699]  ? __pm_rme_resume+0x5c/0x80
[   28.987701]  __scsi_add_device+0x103/0x120
[   28.987709]  ata_scsi_scan_host+0xa3/0x1d0 [libata]
[   28.987716]  async_port_probe+0x43/0x60 [libata]
[   28.987718]  async_run_entry_fn+0x37/0x150
[   28.987722]  process_one_work+0x1d0/0x660

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		   Teamlead Storage & Networking
hare@suse.de			               +49 911 74053 688
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 N�rnberg
GF: F. Imend�rffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton
HRB 21284 (AG N�rnberg)