On Thu, Sep 30, 2021 at 08:56:29AM -0700, Bart Van Assche wrote: > On 9/30/21 5:56 AM, Ming Lei wrote: > > Turns out that blk_mq_freeze_queue() isn't stronger[1] than > > blk_mq_quiesce_queue() because dispatch may still be in-progress after > > queue is frozen, and in several cases, such as switching io scheduler, > > updating nr_requests & wbt latency, we still need to quiesce queue as a > > supplement of freezing queue. > > Is there agreement about this? If not, how about leaving out the above from the > patch description? Yeah, actually the code has been merged, please see the related functions: elevator_switch(), queue_wb_lat_store() and blk_mq_update_nr_requests(). > > > As we need to extend uses of blk_mq_quiesce_queue(), it is inevitable > > for us to need support nested quiesce, especially we can't let > > unquiesce happen when there is quiesce originated from other contexts. > > > > This patch introduces q->mq_quiesce_depth to deal concurrent quiesce, > > and we only unquiesce queue when it is the last/outer-most one of all > > contexts. > > > > One kernel panic issue has been reported[2] when running stress test on > > dm-mpath's updating nr_requests and suspending queue, and the similar > > issue should exist on almost all drivers which use quiesce/unquiesce. > > > > [1] https://marc.info/?l=linux-block&m=150993988115872&w=2 > > [2] https://listman.redhat.com/archives/dm-devel/2021-September/msg00189.html > > Please share the call stack of the kernel oops fixed by [2] since that > call stack is not in the patch description. OK, it is something like the following: [ 145.453672] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.12.0-2.fc30 04/01/2014 [ 145.454104] RIP: 0010:dm_softirq_done+0x46/0x220 [dm_mod] [ 145.454536] Code: 85 ed 0f 84 40 01 00 00 44 0f b6 b7 70 01 00 00 4c 8b a5 18 01 00 00 45 89 f5 f6 47 1d 04 75 57 49 8b 7c 24 08 48 85 ff 74 4d <48> 8b 47 08 48 8b 40 58 48 85 c0 74 40 49 8d 4c 24 50 44 89 f2 48 [ 145.455423] RSP: 0000:ffffa88600003ef8 EFLAGS: 00010282 [ 145.455865] RAX: ffffffffc03fbd10 RBX: ffff979144c00010 RCX: dead000000000200 [ 145.456321] RDX: ffffa88600003f30 RSI: ffff979144c00068 RDI: ffffa88600d01040 [ 145.456764] RBP: ffff979150eb7990 R08: ffff9791bbc27de0 R09: 0000000000000100 [ 145.457205] R10: 0000000000000068 R11: 000000000000004c R12: ffff979144c00138 [ 145.457647] R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000010 [ 145.458080] FS: 00007f57e5d13180(0000) GS:ffff9791bbc00000(0000) knlGS:0000000000000000 [ 145.458516] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 145.458945] CR2: ffffa88600d01048 CR3: 0000000106cf8003 CR4: 0000000000370ef0 [ 145.459382] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [ 145.459815] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 [ 145.460250] Call Trace: [ 145.460779] <IRQ> [ 145.461453] blk_done_softirq+0xa1/0xd0 [ 145.462138] __do_softirq+0xd7/0x2d6 [ 145.462814] irq_exit+0xf7/0x100 [ 145.463480] do_IRQ+0x7f/0xd0 [ 145.464131] common_interrupt+0xf/0xf [ 145.464797] </IRQ> > > > diff --git a/block/blk-mq.c b/block/blk-mq.c > > index 21bf4c3f0825..10f8a3d4e3a1 100644 > > --- a/block/blk-mq.c > > +++ b/block/blk-mq.c > > @@ -209,7 +209,12 @@ EXPORT_SYMBOL_GPL(blk_mq_unfreeze_queue); > > */ > > void blk_mq_quiesce_queue_nowait(struct request_queue *q) > > { > > - blk_queue_flag_set(QUEUE_FLAG_QUIESCED, q); > > + unsigned long flags; > > + > > + spin_lock_irqsave(&q->queue_lock, flags); > > + if (!q->quiesce_depth++) > > + blk_queue_flag_set(QUEUE_FLAG_QUIESCED, q); > > + spin_unlock_irqrestore(&q->queue_lock, flags); > > } > > EXPORT_SYMBOL_GPL(blk_mq_quiesce_queue_nowait); > > Consider using == 0 instead of ! to check whether or not quiesce_depth is > zero to improve code readability. Fine. > > > @@ -250,10 +255,19 @@ EXPORT_SYMBOL_GPL(blk_mq_quiesce_queue); > > */ > > void blk_mq_unquiesce_queue(struct request_queue *q) > > { > > - blk_queue_flag_clear(QUEUE_FLAG_QUIESCED, q); > > + unsigned long flags; > > + bool run_queue = false; > > + > > + spin_lock_irqsave(&q->queue_lock, flags); > > + if (q->quiesce_depth > 0 && !--q->quiesce_depth) { > > + blk_queue_flag_clear(QUEUE_FLAG_QUIESCED, q); > > + run_queue = true; > > + } > > + spin_unlock_irqrestore(&q->queue_lock, flags); > > /* dispatch requests which are inserted during quiescing */ > > - blk_mq_run_hw_queues(q, true); > > + if (run_queue) > > + blk_mq_run_hw_queues(q, true); > > } > > So calling with blk_mq_unquiesce_queue() q->quiesce_depth <= 0 is ignored > quietly? How about triggering a kernel warning for that condition? OK. Thanks, Ming
