Re: [PATCH 3/9] bfq: Split shared queues on move between cgroups

Yu Kuai
2022-12-08T03:53:32Z

Hi, Jan!

在 2022/03/30 20:42, Jan Kara 写道:
> When bfqq is shared by multiple processes it can happen that one of the
> processes gets moved to a different cgroup (or just starts submitting IO
> for different cgroup). In case that happens we need to split the merged
> bfqq as otherwise we will have IO for multiple cgroups in one bfqq and
> we will just account IO time to wrong entities etc.
>
> Similarly if the bfqq is scheduled to merge with another bfqq but the
> merge didn't happen yet, cancel the merge as it need not be valid
> anymore.
>
> CC: stable@vger.kernel.org
> Fixes: e21b7a0b9887 ("block, bfq: add full hierarchical scheduling and cgroups support")
> Signed-off-by: Jan Kara <jack@suse.cz>
> ---
> block/bfq-cgroup.c | 36 +++++++++++++++++++++++++++++++++---
> block/bfq-iosched.c | 2 +-
> block/bfq-iosched.h | 1 +
> 3 files changed, 35 insertions(+), 4 deletions(-)
>
> diff --git a/block/bfq-cgroup.c b/block/bfq-cgroup.c
> index 420eda2589c0..9352f3cc2377 100644
> --- a/block/bfq-cgroup.c
> +++ b/block/bfq-cgroup.c
> @@ -743,9 +743,39 @@ static struct bfq_group *__bfq_bic_change_cgroup(struct bfq_data *bfqd,
> }
>
> if (sync_bfqq) {
> - entity = &sync_bfqq->entity;
> - if (entity->sched_data != &bfqg->sched_data)
> - bfq_bfqq_move(bfqd, sync_bfqq, bfqg);
> + if (!sync_bfqq->new_bfqq && !bfq_bfqq_coop(sync_bfqq)) {
> + /* We are the only user of this bfqq, just move it */
> + if (sync_bfqq->entity.sched_data != &bfqg->sched_data)
> + bfq_bfqq_move(bfqd, sync_bfqq, bfqg);
> + } else {
> + struct bfq_queue *bfqq;
> +
> + /*
> + * The queue was merged to a different queue. Check
> + * that the merge chain still belongs to the same
> + * cgroup.
> + */
> + for (bfqq = sync_bfqq; bfqq; bfqq = bfqq->new_bfqq)
> + if (bfqq->entity.sched_data !=
> + &bfqg->sched_data)
> + break;
> + if (bfqq) {
> + /*
> + * Some queue changed cgroup so the merge is
> + * not valid anymore. We cannot easily just
> + * cancel the merge (by clearing new_bfqq) as
> + * there may be other processes using this
> + * queue and holding refs to all queues below
> + * sync_bfqq->new_bfqq. Similarly if the merge
> + * already happened, we need to detach from
> + * bfqq now so that we cannot merge bio to a
> + * request from the old cgroup.
> + */
> + bfq_put_cooperator(sync_bfqq);
> + bfq_release_process_ref(bfqd, sync_bfqq);
> + bic_set_bfqq(bic, NULL, 1);
> + }
> + }
> }
Our test found a use-after-free while accessing bfqq->bic->bfqq[] ([1]),
and I really suspect the above change.

1) init state, 2 thread, 2 bic, and 2 bfqq

bic1->bfqq = bfqq1
bfqq1->bic = bic1
bic2->bfqq = bfqq2
bfqq2->bic = bic2

2) bfqq1 and bfqq2 is merged
bic1->bfqq = bfqq2
bfqq1->bic = NULL
bic2->bfqq = bfqq2
bfqq2->bic = NULL

3) bfqq1 issue a io, before such io reaches bfq, move t1 to a new
cgroup, and issues a new io. If the new io reaches bfq first:
bic1->bfqq = NULL
bfqq1->bic = NULL
bic2->bfqq = bfqq2
bfqq2->bic = NULL

4) while handling the new io, a new bfqq is created
bic1->bfqq = bfqq3
bfqq3->bic = bic1
bic2->bfqq = bfqq2
bfqq2->bic = NULL

5) the old io reaches bfq, corresponding bic is got from rq:
bic1->bfqq = bfqq3
bfqq3->bic = bic1
bic2->bfqq = bfqq2
bfqq2->bic = bic1

Here comes up the problematic state, two different bfqq point to the
same bic. And furthermore, if t1 exit and all the io from t1 is done,
bic1 can be freed while bfqq2->bic still points to bic1.

I'm not quite sure about how the bic is working, but I think it make
sense to make sure that bfqq->bic never point to a bic that
corresponding thread doesn't match. Something like below:

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index a72304c728fc..22bbc9d45ddf 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -6757,7 +6757,8 @@ static struct bfq_queue *bfq_init_rq(struct
request *rq)
* addition, if the queue has also just been split, we have to
* resume its state.
*/
- if (likely(bfqq != &bfqd->oom_bfqq) && bfqq_process_refs(bfqq)
== 1) {
+ if (likely(bfqq != &bfqd->oom_bfqq) && bfqq_process_refs(bfqq)
== 1 &&
+ bfqq->org_bic == bic) {
bfqq->bic = bic;

[1]
[605854.098478]
==================================================================
[605854.099367] BUG: KASAN: use-after-free in bfq_select_queue+0x378/0xa30
[605854.100133] Read of size 8 at addr ffff88810efb42d8 by task
fsstress/2318352

[605854.101213] CPU: 6 PID: 2318352 Comm: fsstress Kdump: loaded Not
tainted 5.10.0-60.18.0.50.h602.kasan.eulerosv2r11.x86_64 #1
[605854.101218] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
BIOS rel-1.12.1-0-ga5cab58-20220320_160524-szxrtosci10000 04/01/2014
[605854.101221] Call Trace:
[605854.101231] dump_stack+0x9c/0xd3
[605854.101240] print_address_description.constprop.0+0x19/0x170
[605854.101247] ? bfq_select_queue+0x378/0xa30
[605854.101254] __kasan_report.cold+0x6c/0x84
[605854.101261] ? bfq_select_queue+0x378/0xa30
[605854.101267] kasan_report+0x3a/0x50
[605854.101273] bfq_select_queue+0x378/0xa30
[605854.101279] ? bfq_bfqq_expire+0x6c0/0x6c0
[605854.101286] ? bfq_mark_bfqq_busy+0x1f/0x30
[605854.101293] ? _raw_spin_lock_irq+0x7b/0xd0
[605854.101299] __bfq_dispatch_request+0x1c4/0x220
[605854.101306] bfq_dispatch_request+0xe8/0x130
[605854.101313] __blk_mq_do_dispatch_sched+0x3f4/0x560
[605854.101320] ? blk_mq_sched_mark_restart_hctx+0x50/0x50
[605854.101326] ? bfq_init_rq+0x128/0x940
[605854.101333] ? pvclock_clocksource_read+0xf6/0x1d0
[605854.101339] blk_mq_do_dispatch_sched+0x62/0xb0
[605854.101345] __blk_mq_sched_dispatch_requests+0x215/0x2a0
[605854.101351] ? blk_mq_do_dispatch_ctx+0x3a0/0x3a0
[605854.101358] ? bfq_insert_request+0x193/0x3f0
[605854.101364] blk_mq_sched_dispatch_requests+0x8f/0xd0
[605854.101370] __blk_mq_run_hw_queue+0x98/0x180
[605854.101377] __blk_mq_delay_run_hw_queue+0x22b/0x240
[605854.101383] ? bfq_asymmetric_scenario+0x160/0x160
[605854.101389] blk_mq_run_hw_queue+0xe3/0x190
[605854.101396] ? bfq_insert_request+0x3f0/0x3f0
[605854.101401] blk_mq_sched_insert_requests+0x107/0x200
[605854.101408] blk_mq_flush_plug_list+0x26e/0x3c0
[605854.101415] ? blk_mq_insert_requests+0x250/0x250
[605854.101422] ? blk_check_plugged+0x190/0x190
[605854.101429] blk_finish_plug+0x63/0x90
[605854.101436] __iomap_dio_rw+0x7b5/0x910
[605854.101443] ? iomap_dio_actor+0x150/0x150
[605854.101450] ? userns_put+0x70/0x70
[605854.101456] ? userns_put+0x70/0x70
[605854.101463] ? avc_has_perm_noaudit+0x1d0/0x1d0
[605854.101468] ? down_read+0xd5/0x1a0
[605854.101474] ? down_read_killable+0x1b0/0x1b0
[605854.101479] ? from_kgid+0xa0/0xa0
[605854.101485] iomap_dio_rw+0x36/0x80
[605854.101544] ext4_dio_read_iter+0x146/0x190 [ext4]
[605854.101602] ext4_file_read_iter+0x1e2/0x230 [ext4]
[605854.101609] new_sync_read+0x29f/0x400
[605854.101615] ? default_llseek+0x160/0x160
[605854.101621] ? find_isec_ns+0x8d/0x2e0
[605854.101627] ? avc_policy_seqno+0x27/0x40
[605854.101633] ? selinux_file_permission+0x34/0x180
[605854.101641] ? security_file_permission+0x135/0x2b0
[605854.101648] vfs_read+0x24e/0x2d0
[605854.101654] ksys_read+0xd5/0x1b0
[605854.101661] ? __ia32_sys_pread64+0x160/0x160
[605854.101667] ? __audit_syscall_entry+0x1cc/0x220
[605854.101675] do_syscall_64+0x33/0x40
[605854.101681] entry_SYSCALL_64_after_hwframe+0x61/0xc6
[605854.101686] RIP: 0033:0x7ff05f96fe62
[605854.101705] Code: c0 e9 b2 fe ff ff 50 48 8d 3d 12 04 0c 00 e8 b5 fe
01 00 0f 1f 44 00 00 f3 0f 1e fa 64 8b 04 25 18 00 00 00 85 c0 75 10 0f
05 <48> 3d 00 f0 ff ff 77 56 c3 0f 1f 44 00 00 48 83 ec 28 48 89 54 24
[605854.101709] RSP: 002b:00007fffd30c0ff8 EFLAGS: 00000246 ORIG_RAX:
0000000000000000
[605854.101717] RAX: ffffffffffffffda RBX: 00000000000000a5 RCX:
00007ff05f96fe62
[605854.101721] RDX: 000000000001d000 RSI: 0000000001ffc000 RDI:
0000000000000003
[605854.101724] RBP: 0000000000000003 R08: 0000000002019000 R09:
0000000000000000
[605854.101729] R10: 00007ff05fa65290 R11: 0000000000000246 R12:
0000000000131800
[605854.101732] R13: 000000000001d000 R14: 0000000000000000 R15:
0000000001ffc000

[605854.102003] Allocated by task 2318348:
[605854.102489] kasan_save_stack+0x1b/0x40
[605854.102495] __kasan_kmalloc.constprop.0+0xb5/0xe0
[605854.102501] kmem_cache_alloc_node+0x15d/0x480
[605854.102505] ioc_create_icq+0x68/0x2e0
[605854.102510] blk_mq_sched_assign_ioc+0xbc/0xd0
[605854.102516] blk_mq_rq_ctx_init+0x4b0/0x600
[605854.102521] __blk_mq_alloc_request+0x21f/0x2e0
[605854.102526] blk_mq_submit_bio+0x27a/0xd60
[605854.102532] __submit_bio_noacct_mq+0x10b/0x270
[605854.102538] submit_bio_noacct+0x13d/0x150
[605854.102543] submit_bio+0xbf/0x280
[605854.102548] iomap_dio_submit_bio+0x155/0x180
[605854.102553] iomap_dio_bio_actor+0x2f0/0x770
[605854.102557] iomap_dio_actor+0xd9/0x150
[605854.102562] iomap_apply+0x1d2/0x4f0
[605854.102567] __iomap_dio_rw+0x43a/0x910
[605854.102572] iomap_dio_rw+0x36/0x80
[605854.102628] ext4_dio_write_iter+0x46f/0x730 [ext4]
[605854.102684] ext4_file_write_iter+0xd8/0x100 [ext4]
[605854.102689] new_sync_write+0x2ac/0x3a0
[605854.102701] vfs_write+0x365/0x430
[605854.102707] ksys_write+0xd5/0x1b0
[605854.102712] do_syscall_64+0x33/0x40
[605854.102718] entry_SYSCALL_64_after_hwframe+0x61/0xc6

[605854.102984] Freed by task 2320929:
[605854.103434] kasan_save_stack+0x1b/0x40
[605854.103439] kasan_set_track+0x1c/0x30
[605854.103444] kasan_set_free_info+0x20/0x40
[605854.103449] __kasan_slab_free+0x151/0x180
[605854.103454] kmem_cache_free+0x9e/0x540
[605854.103461] rcu_do_batch+0x292/0x700
[605854.103465] rcu_core+0x270/0x2d0
[605854.103471] __do_softirq+0xfd/0x402

[605854.103741] Last call_rcu():
[605854.104141] kasan_save_stack+0x1b/0x40
[605854.104146] kasan_record_aux_stack+0xa8/0xf0
[605854.104150] __call_rcu+0xa4/0x3a0
[605854.104155] ioc_release_fn+0x45/0x120
[605854.104161] process_one_work+0x3c5/0x730
[605854.104167] worker_thread+0x93/0x650
[605854.104172] kthread+0x1ba/0x210
[605854.104178] ret_from_fork+0x22/0x30

[605854.104440] Second to last call_rcu():
[605854.104930] kasan_save_stack+0x1b/0x40
[605854.104935] kasan_record_aux_stack+0xa8/0xf0
[605854.104939] __call_rcu+0xa4/0x3a0
[605854.104944] ioc_release_fn+0x45/0x120
[605854.104949] process_one_work+0x3c5/0x730
[605854.104955] worker_thread+0x93/0x650
[605854.104960] kthread+0x1ba/0x210
[605854.104965] ret_from_fork+0x22/0x30

[605854.105229] The buggy address belongs to the object at ffff88810efb42a0
which belongs to the cache bfq_io_cq of size 160
[605854.106659] The buggy address is located 56 bytes inside of
160-byte region [ffff88810efb42a0, ffff88810efb4340)
[605854.108021] The buggy address belongs to the page:
[605854.108608] page:00000000a519c14c refcount:1 mapcount:0
mapping:0000000000000000 index:0xffff88810efb4000 pfn:0x10efb4
[605854.108612] head:00000000a519c14c order:1 compound_mapcount:0
[605854.108620] flags:
0x17ffffc0010200(slab|head|node=0|zone=2|lastcpupid=0x1fffff)
[605854.108628] raw: 0017ffffc0010200 0000000000000000 dead000000000122
ffff8881407c8600
[605854.108635] raw: ffff88810efb4000 000000008024001a 00000001ffffffff
0000000000000000
[605854.108639] page dumped because: kasan: bad access detected

[605854.108909] Memory state around the buggy address:
[605854.109494] ffff88810efb4180: fc fc fc fc fc fc fc fc fb fb fb fb
fb fb fb fb
[605854.110323] ffff88810efb4200: fb fb fb fb fb fb fb fb fb fb fb fb
fc fc fc fc
[605854.111151] >ffff88810efb4280: fc fc fc fc fa fb fb fb fb fb fb fb
fb fb fb fb
[605854.111978] ^
[605854.112692] ffff88810efb4300: fb fb fb fb fb fb fb fb fc fc fc fc
fc fc fc fc
[605854.113522] ffff88810efb4380: fb fb fb fb fb fb fb fb fb fb fb fb
fb fb fb fb
[605854.114350]
==================================================================