This is a note to let you know that I've just added the patch titled
block, bfq: fix null pointer dereference in bfq_bio_bfqg()
to the 5.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
block-bfq-fix-null-pointer-dereference-in-bfq_bio_bf.patch
and it can be found in the queue-5.10 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 86eba5138ccd2cc0ef78c2af6f3a4a298db12b43
Author: Yu Kuai <yukuai3@xxxxxxxxxx>
Date: Tue Nov 8 18:34:34 2022 +0800
block, bfq: fix null pointer dereference in bfq_bio_bfqg()
[ Upstream commit f02be9002c480cd3ec0fcf184ad27cf531bd6ece ]
Out test found a following problem in kernel 5.10, and the same problem
should exist in mainline:
BUG: kernel NULL pointer dereference, address: 0000000000000094
PGD 0 P4D 0
Oops: 0000 [#1] SMP
CPU: 7 PID: 155 Comm: kworker/7:1 Not tainted 5.10.0-01932-g19e0ace2ca1d-dirty 4
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS ?-20190727_073836-b4
Workqueue: kthrotld blk_throtl_dispatch_work_fn
RIP: 0010:bfq_bio_bfqg+0x52/0xc0
Code: 94 00 00 00 00 75 2e 48 8b 40 30 48 83 05 35 06 c8 0b 01 48 85 c0 74 3d 4b
RSP: 0018:ffffc90001a1fba0 EFLAGS: 00010002
RAX: ffff888100d60400 RBX: ffff8881132e7000 RCX: 0000000000000000
RDX: 0000000000000017 RSI: ffff888103580a18 RDI: ffff888103580a18
RBP: ffff8881132e7000 R08: 0000000000000000 R09: ffffc90001a1fe10
R10: 0000000000000a20 R11: 0000000000034320 R12: 0000000000000000
R13: ffff888103580a18 R14: ffff888114447000 R15: 0000000000000000
FS: 0000000000000000(0000) GS:ffff88881fdc0000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000094 CR3: 0000000100cdb000 CR4: 00000000000006e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
bfq_bic_update_cgroup+0x3c/0x350
? ioc_create_icq+0x42/0x270
bfq_init_rq+0xfd/0x1060
bfq_insert_requests+0x20f/0x1cc0
? ioc_create_icq+0x122/0x270
blk_mq_sched_insert_requests+0x86/0x1d0
blk_mq_flush_plug_list+0x193/0x2a0
blk_flush_plug_list+0x127/0x170
blk_finish_plug+0x31/0x50
blk_throtl_dispatch_work_fn+0x151/0x190
process_one_work+0x27c/0x5f0
worker_thread+0x28b/0x6b0
? rescuer_thread+0x590/0x590
kthread+0x153/0x1b0
? kthread_flush_work+0x170/0x170
ret_from_fork+0x1f/0x30
Modules linked in:
CR2: 0000000000000094
---[ end trace e2e59ac014314547 ]---
RIP: 0010:bfq_bio_bfqg+0x52/0xc0
Code: 94 00 00 00 00 75 2e 48 8b 40 30 48 83 05 35 06 c8 0b 01 48 85 c0 74 3d 4b
RSP: 0018:ffffc90001a1fba0 EFLAGS: 00010002
RAX: ffff888100d60400 RBX: ffff8881132e7000 RCX: 0000000000000000
RDX: 0000000000000017 RSI: ffff888103580a18 RDI: ffff888103580a18
RBP: ffff8881132e7000 R08: 0000000000000000 R09: ffffc90001a1fe10
R10: 0000000000000a20 R11: 0000000000034320 R12: 0000000000000000
R13: ffff888103580a18 R14: ffff888114447000 R15: 0000000000000000
FS: 0000000000000000(0000) GS:ffff88881fdc0000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000094 CR3: 0000000100cdb000 CR4: 00000000000006e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Root cause is quite complex:
1) use bfq elevator for the test device.
2) create a cgroup CG
3) config blk throtl in CG
blkg_conf_prep
blkg_create
4) create a thread T1 and issue async io in CG:
bio_init
bio_associate_blkg
...
submit_bio
submit_bio_noacct
blk_throtl_bio -> io is throttled
// io submit is done
5) switch elevator:
bfq_exit_queue
blkcg_deactivate_policy
list_for_each_entry(blkg, &q->blkg_list, q_node)
blkg->pd[] = NULL
// bfq policy is removed
5) thread t1 exist, then remove the cgroup CG:
blkcg_unpin_online
blkcg_destroy_blkgs
blkg_destroy
list_del_init(&blkg->q_node)
// blkg is removed from queue list
6) switch elevator back to bfq
bfq_init_queue
bfq_create_group_hierarchy
blkcg_activate_policy
list_for_each_entry_reverse(blkg, &q->blkg_list)
// blkg is removed from list, hence bfq policy is still NULL
7) throttled io is dispatched to bfq:
bfq_insert_requests
bfq_init_rq
bfq_bic_update_cgroup
bfq_bio_bfqg
bfqg = blkg_to_bfqg(blkg)
// bfqg is NULL because bfq policy is NULL
The problem is only possible in bfq because only bfq can be deactivated and
activated while queue is online, while others can only be deactivated while
the device is removed.
Fix the problem in bfq by checking if blkg is online before calling
blkg_to_bfqg().
Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
Reviewed-by: Jan Kara <jack@xxxxxxx>
Link: https://lore.kernel.org/r/20221108103434.2853269-1-yukuai1@xxxxxxxxxxxxxxx
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/block/bfq-cgroup.c b/block/bfq-cgroup.c
index be6733558b83..badb90352bf3 100644
--- a/block/bfq-cgroup.c
+++ b/block/bfq-cgroup.c
@@ -611,6 +611,10 @@ struct bfq_group *bfq_bio_bfqg(struct bfq_data *bfqd, struct bio *bio)
struct bfq_group *bfqg;
while (blkg) {
+ if (!blkg->online) {
+ blkg = blkg->parent;
+ continue;
+ }
bfqg = blkg_to_bfqg(blkg);
if (bfqg->online) {
bio_associate_blkg_from_css(bio, &blkg->blkcg->css);
