Re: [PATCH V2 00/16] Introduce the BFQ I/O scheduler

[Bart Van Assche]

On Fri, 2017-03-31 at 14:47 +0200, Paolo Valente wrote:
> [ ... ]

Hello Paolo,

Is the git tree that is available at https://github.com/Algodev-github/bfq-mq
appropriate for testing BFQ? If I merge that tree with v4.11-rc6 and if I run
the srp-test software against that tree as follows:

    ./run_tests -e bfq-mq -t 02-mq

then the following appears on the console:

[ 2748.650352] BUG: unable to handle kernel NULL pointer dereference at 00000000000000d0
[ 2748.650442] IP: __bfq_insert_request+0x26/0x650 [bfq_mq_iosched]
[ 2748.650509] PGD 0 
[ 2748.650511] 
[ 2748.650585] Oops: 0000 [#1] SMP
[ 2748.651107] CPU: 9 PID: 10772 Comm: kworker/9:2H Tainted: G          I     4.11.0-rc6-dbg+ #1
[ 2748.651191] Workqueue: kblockd blk_mq_requeue_work
[ 2748.651228] task: ffff88037c808040 task.stack: ffffc90003b4c000
[ 2748.651268] RIP: 0010:__bfq_insert_request+0x26/0x650 [bfq_mq_iosched]
[ 2748.651307] RSP: 0018:ffffc90003b4f9d8 EFLAGS: 00010002
[ 2748.651345] RAX: 0000000000000001 RBX: 0000000000000000 RCX: 0000000000000001
[ 2748.651383] RDX: 0000000000000001 RSI: ffff880377f52e80 RDI: ffff880401f774e8
[ 2748.651423] RBP: ffffc90003b4fa80 R08: 9093955f00000000 R09: 0000000000000001
[ 2748.651464] R10: ffffc90003b4fa00 R11: ffffffffa06d0d53 R12: ffff880401f77840
[ 2748.651506] R13: ffff880401f774e8 R14: ffff880378a451e0 R15: 0000000000000000
[ 2748.651547] FS:  0000000000000000(0000) GS:ffff88046f040000(0000) knlGS:0000000000000000
[ 2748.651588] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 2748.651626] CR2: 00000000000000d0 CR3: 0000000001c0f000 CR4: 00000000001406e0
[ 2748.651664] Call Trace:
[ 2748.651778]  bfq_insert_request+0x83/0x280 [bfq_mq_iosched]
[ 2748.651934]  bfq_insert_requests+0x50/0x70 [bfq_mq_iosched]
[ 2748.651975]  blk_mq_sched_insert_request+0x11e/0x170
[ 2748.652015]  blk_insert_cloned_request+0xb6/0x1f0
[ 2748.652361]  map_request+0x13c/0x290 [dm_mod]
[ 2748.652403]  dm_mq_queue_rq+0x90/0x160 [dm_mod]
[ 2748.652441]  blk_mq_dispatch_rq_list+0x1f2/0x3e0
[ 2748.652479]  blk_mq_sched_dispatch_requests+0xf1/0x190
[ 2748.652516]  __blk_mq_run_hw_queue+0x12d/0x1c0
[ 2748.652553]  __blk_mq_delay_run_hw_queue+0xe3/0xf0
[ 2748.652593]  blk_mq_run_hw_queues+0x5c/0x80
[ 2748.652632]  blk_mq_requeue_work+0x132/0x150
[ 2748.652671]  process_one_work+0x206/0x6a0
[ 2748.652709]  worker_thread+0x49/0x4a0
[ 2748.652745]  kthread+0x107/0x140
[ 2748.652854]  ret_from_fork+0x2e/0x40
[ 2748.652891] Code: ff 0f 1f 40 00 55 48 89 e5 41 57 41 56 41 55 41 54 53 48 83 c4 80 8b 87 58 03 00 00 48 8b 9e b0 00 00 00 85 c0 0f 84 8b 04 00 00 <48> 8b 83 d0 00 00 00 48 85 c0 0f 84 63 04 00 00
48 83 e8 10 48 
[ 2748.653049] RIP: __bfq_insert_request+0x26/0x650 [bfq_mq_iosched] RSP: ffffc90003b4f9d8
[ 2748.653090] CR2: 00000000000000d0

The crash address corresponds to the following source code according to gdb:

(gdb) list *(__bfq_insert_request+0x26)
0xd6f6 is in __bfq_insert_request (block/bfq-mq-iosched.c:4430).
4425
4426    static void __bfq_insert_request(struct bfq_data *bfqd, struct request *rq)
4427    {
4428            struct bfq_queue *bfqq = RQ_BFQQ(rq), *new_bfqq;
4429
4430            assert_spin_locked(&bfqd->lock);
4431
4432            bfq_log_bfqq(bfqd, bfqq, "__insert_req: rq %p bfqq %p", rq, bfqq);
4433
4434            /*

Bart.