On 5/22/18 11:17 AM, Jens Axboe wrote: > On 5/22/18 10:44 AM, Jens Axboe wrote: >> >> On 5/22/18 10:25 AM, Bart Van Assche wrote: >>> Recently the blk-mq timeout handling code was reworked. See also Tejun >>> Heo, "[PATCHSET v4] blk-mq: reimplement timeout handling", 08 Jan 2018 >>> (https://www.mail-archive.com/linux-block@xxxxxxxxxxxxxxx/msg16985.html). >>> This patch reworks the blk-mq timeout handling code again. The timeout >>> handling code is simplified by introducing a state machine per request. >>> This change avoids that the blk-mq timeout handling code ignores >>> completions that occur after blk_mq_check_expired() has been called and >>> before blk_mq_rq_timed_out() has been called. >> >> I'll take a look at this again, getting rid of cmpxchg64 makes me >> much more comfortable. > > FWIW, a quick pass on runtime testing works fine. As expected, it's > more efficient than what's currently in the kernel, testing with both > null_blk (1 and nr_cpus worth of queues), and nvme as well. A huge win > is that we shrink the request size from 360 bytes to 312, and I did > a small followup patch that brings that to 304. That's a 15% reduction, > massive. Ran into this, running block/014 from blktests: [ 5744.949839] run blktests block/014 at 2018-05-22 12:41:25 [ 5750.723000] null: rq 00000000ff68f103 timed out [ 5750.728181] WARNING: CPU: 45 PID: 2480 at block/blk-mq.c:585 __blk_mq_complete_request+0xa6/0x0 [ 5750.738187] Modules linked in: null_blk(+) configfs nvme nvme_core sb_edac x86_pkg_temp_therma] [ 5750.765509] CPU: 45 PID: 2480 Comm: kworker/45:1H Not tainted 4.17.0-rc6+ #712 [ 5750.774087] Hardware name: Dell Inc. PowerEdge T630/0NT78X, BIOS 2.3.4 11/09/2016 [ 5750.783369] Workqueue: kblockd blk_mq_timeout_work [ 5750.789223] RIP: 0010:__blk_mq_complete_request+0xa6/0x110 [ 5750.795850] RSP: 0018:ffff883ffb417d68 EFLAGS: 00010202 [ 5750.802187] RAX: 0000000000000003 RBX: ffff881ff100d800 RCX: 0000000000000000 [ 5750.810649] RDX: ffff88407fd9e040 RSI: ffff88407fd956b8 RDI: ffff881ff100d800 [ 5750.819119] RBP: ffffe8ffffd91800 R08: 0000000000000000 R09: ffffffff82066eb8 [ 5750.827588] R10: ffff883ffa386138 R11: ffff883ffa385900 R12: 0000000000000001 [ 5750.836050] R13: ffff881fe7da6000 R14: 0000000000000020 R15: 0000000000000002 [ 5750.844529] FS: 0000000000000000(0000) GS:ffff88407fd80000(0000) knlGS:0000000000000000 [ 5750.854482] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 5750.861397] CR2: 00007ffc92f97f68 CR3: 000000000201d005 CR4: 00000000003606e0 [ 5750.869861] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [ 5750.878333] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 [ 5750.886805] Call Trace: [ 5750.890033] bt_iter+0x42/0x50 [ 5750.894000] blk_mq_queue_tag_busy_iter+0x12b/0x220 [ 5750.899941] ? blk_mq_tag_to_rq+0x20/0x20 [ 5750.904913] ? __rcu_read_unlock+0x50/0x50 [ 5750.909978] ? blk_mq_tag_to_rq+0x20/0x20 [ 5750.914948] blk_mq_timeout_work+0x14b/0x240 [ 5750.920220] process_one_work+0x21b/0x510 [ 5750.925197] worker_thread+0x3a/0x390 [ 5750.929781] ? process_one_work+0x510/0x510 [ 5750.934944] kthread+0x11c/0x140 [ 5750.939028] ? kthread_create_worker_on_cpu+0x50/0x50 [ 5750.945169] ret_from_fork+0x1f/0x30 [ 5750.949656] Code: 48 02 00 00 80 e6 80 74 29 8b 95 80 00 00 00 44 39 e2 75 3b 48 89 df ff 90 2 [ 5750.972139] ---[ end trace 40065cb1764bf500 ]--- which is this: WARN_ON_ONCE(blk_mq_rq_state(rq) != MQ_RQ_COMPLETE); hitting when blk_mq_terminate_expired() completes the request through BLK_EH_HANDLED. -- Jens Axboe
