[lvc-project] [PATCH] block: bfq fix null pointer dereference of bfqg in bfq_bio_bfqg()

[Artem Chernyshev]

It is possible for bfqg to be NULL after being initialized as result of
blkg_to_bfqg() function.

That was achieved on kernel 5.15.78, but should exist in mainline as
well

host1 login: [ 460.855794] watchdog: watchdog0: watchdog did not stop!
[  898.944512] BUG: kernel NULL pointer dereference, address: 0000000000000094
[  899.285776] #PF: supervisor read access in kernel mode
[  899.536511] #PF: error_code(0x0000) - not-present page
[  899.647305]  connection4:0: detected conn error (1020)
[  899.786794] PGD 0 P4D 0
[  899.786799] Oops: 0000 [#1] SMP PTI
[  899.786802] CPU: 15 PID: 6073 Comm: ID iothread1 Not tainted 5.15.78-1.el7virt.x86_64 #1
[  899.786804] Hardware name: HP ProLiant DL360 Gen9/ProLiant DL360 Gen9, BIOS P89 10/21/2019
[  899.786806] RIP: 0010:bfq_bio_bfqg+0x26/0x80
[  901.325944] Code: 0f 1f 40 00 0f 1f 44 00 00 55 48 89 fd 48 89 f7 53 48 8b 56 48 48 85 d2
74 32 48 63 05 83 7f 35 01 48 83 c0 16 48 8b 5c c2 08 <80> bb 94 00 00 00 00 00
[  902.237825] RSP: 0018:ffffae2649437688 EFLAGS: 00010002
[  902.493396] RAX: 0000000000000019 RBX: 0000000000000000 RCX: dead000000000122
[  902.841529] RDX: ffff8b6012cb3a00 RSI: ffff8b71002bbed0 RDI: ffff8b71002bbed0
[  903.189374] RBP: ffff8b601c46e800 R08: ffffae26494377c8 R09: 0000000000000000
[  903.532985] R10: 0000000000000001 R11: 0000000000000008 R12: ffff8b6f844c5b30
[  903.880809] R13: ffff8b601c46e800 R14: ffffae2649437760 R15: ffff8b601c46e800
[  904.220054] FS:  00007fec2fc4a700(0000) GS:ffff8b7f7f640000(0000) kn1GS:00000000000000000
[  904.614349] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  904.894717] CR2: 0000000000000094 CR3: 0000000111fd8002 CR4: 00000000003726e0
[  905.243702] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  905.592493] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  905.936859] Call Trace:
[  906.055955] <TASK>
[  906.158109] bfq_bic_update_cgroup+0x2c/0x1f0
[  906.371057] bfq_insert_requests+0x2c2/0x1fb0
[  906.579207] blk_mq_sched_insert_request+0xc2/0x140
[  906.817640] __blk_mq_try_issue_directly+0xe0/0x1f0
[  907.055737] blk_mq_request_issue_directly+0x4e/0xa0
[  907.298547] dm_mq_queue_rq+0x217/0x3e0
[  907.485935] blk_mq_dispatch_rq_list+0x14b/0x860
[  907.711973] ? sbitmap_get+0x87/0x1a0
[  907.890370] blk_mq_do_dispatch_sched+0x350/0x3b0
[  908.074869] NMI watchdog: Watchdog detected hard LOCKUP on cpu 40

Fixes: 075a53b78b81 ("bfq: Make sure bfqg for which we are queueing requests is online")
Co-developed-by: Anton Fadeev <anton.fadeev at red-soft.ru>
Signed-off-by: Anton Fadeev <anton.fadeev at red-soft.ru>
Signed-off-by: Artem Chernyshev <artem.chernyshev at red-soft.ru>
---
 block/bfq-cgroup.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/block/bfq-cgroup.c b/block/bfq-cgroup.c
index 1b2829e99dad..d4e9428cdbe5 100644
--- a/block/bfq-cgroup.c
+++ b/block/bfq-cgroup.c
@@ -616,7 +616,7 @@ struct bfq_group *bfq_bio_bfqg(struct bfq_data *bfqd, struct bio *bio)
 			continue;
 		}
 		bfqg = blkg_to_bfqg(blkg);
-		if (bfqg->online) {
+		if (bfqg && bfqg->online) {
 			bio_associate_blkg_from_css(bio, &blkg->blkcg->css);
 			return bfqg;
 		}
-- 
2.30.3