Out test report a null pointer dereference:
[ 168.534653]
==================================================================
[ 168.535614] Disabling lock debugging due to kernel taint
[ 168.536346] BUG: kernel NULL pointer dereference, address:
0000000000000008
[ 168.537274] #PF: supervisor read access in kernel mode
[ 168.537964] #PF: error_code(0x0000) - not-present page
[ 168.538667] PGD 0 P4D 0
[ 168.539025] Oops: 0000 [#1] PREEMPT SMP KASAN
[ 168.539656] CPU: 13 PID: 759 Comm: bash Tainted: G B
5.15.0-rc2-next-202100
[ 168.540954] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
BIOS ?-20190727_0738364
[ 168.542736] RIP: 0010:bfq_pd_init+0x88/0x1e0
[ 168.543318] Code: 98 00 00 00 e8 c9 e4 5b ff 4c 8b 65 00 49 8d 7c
24 08 e8 bb e4 5b ff 4d0
[ 168.545803] RSP: 0018:ffff88817095f9c0 EFLAGS: 00010002
[ 168.546497] RAX: 0000000000000001 RBX: ffff888101a1c000 RCX:
0000000000000000
[ 168.547438] RDX: 0000000000000003 RSI: 0000000000000002 RDI:
ffff888106553428
[ 168.548402] RBP: ffff888106553400 R08: ffffffff961bcaf4 R09:
0000000000000001
[ 168.549365] R10: ffffffffa2e16c27 R11: fffffbfff45c2d84 R12:
0000000000000000
[ 168.550291] R13: ffff888101a1c098 R14: ffff88810c7a08c8 R15:
ffffffffa55541a0
[ 168.551221] FS: 00007fac75227700(0000) GS:ffff88839ba80000(0000)
knlGS:0000000000000000
[ 168.552278] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 168.553040] CR2: 0000000000000008 CR3: 0000000165ce7000 CR4:
00000000000006e0
[ 168.554000] DR0: 0000000000000000 DR1: 0000000000000000 DR2:
0000000000000000
[ 168.554929] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7:
0000000000000400
[ 168.555888] Call Trace:
[ 168.556221] <TASK>
[ 168.556510] blkg_create+0x1c0/0x8c0
[ 168.556989] blkg_conf_prep+0x574/0x650
[ 168.557502] ? stack_trace_save+0x99/0xd0
[ 168.558033] ? blkcg_conf_open_bdev+0x1b0/0x1b0
[ 168.558629] tg_set_conf.constprop.0+0xb9/0x280
[ 168.559231] ? kasan_set_track+0x29/0x40
[ 168.559758] ? kasan_set_free_info+0x30/0x60
[ 168.560344] ? tg_set_limit+0xae0/0xae0
[ 168.560853] ? do_sys_openat2+0x33b/0x640
[ 168.561383] ? do_sys_open+0xa2/0x100
[ 168.561877] ? __x64_sys_open+0x4e/0x60
[ 168.562383] ? __kasan_check_write+0x20/0x30
[ 168.562951] ? copyin+0x48/0x70
[ 168.563390] ? _copy_from_iter+0x234/0x9e0
[ 168.563948] tg_set_conf_u64+0x17/0x20
[ 168.564467] cgroup_file_write+0x1ad/0x380
[ 168.565014] ? cgroup_file_poll+0x80/0x80
[ 168.565568] ? __mutex_lock_slowpath+0x30/0x30
[ 168.566165] ? pgd_free+0x100/0x160
[ 168.566649] kernfs_fop_write_iter+0x21d/0x340
[ 168.567246] ? cgroup_file_poll+0x80/0x80
[ 168.567796] new_sync_write+0x29f/0x3c0
[ 168.568314] ? new_sync_read+0x410/0x410
[ 168.568840] ? __handle_mm_fault+0x1c97/0x2d80
[ 168.569425] ? copy_page_range+0x2b10/0x2b10
[ 168.570007] ? _raw_read_lock_bh+0xa0/0xa0
[ 168.570622] vfs_write+0x46e/0x630
[ 168.571091] ksys_write+0xcd/0x1e0
[ 168.571563] ? __x64_sys_read+0x60/0x60
[ 168.572081] ? __kasan_check_write+0x20/0x30
[ 168.572659] ? do_user_addr_fault+0x446/0xff0
[ 168.573264] __x64_sys_write+0x46/0x60
[ 168.573774] do_syscall_64+0x35/0x80
[ 168.574264] entry_SYSCALL_64_after_hwframe+0x44/0xae
[ 168.574960] RIP: 0033:0x7fac74915130
[ 168.575456] Code: 73 01 c3 48 8b 0d 58 ed 2c 00 f7 d8 64 89 01 48
83 c8 ff c3 66 0f 1f 444
[ 168.577969] RSP: 002b:00007ffc3080e288 EFLAGS: 00000246 ORIG_RAX:
0000000000000001
[ 168.578986] RAX: ffffffffffffffda RBX: 0000000000000009 RCX:
00007fac74915130
[ 168.579937] RDX: 0000000000000009 RSI: 000056007669f080 RDI:
0000000000000001
[ 168.580884] RBP: 000056007669f080 R08: 000000000000000a R09:
00007fac75227700
[ 168.581841] R10: 000056007655c8f0 R11: 0000000000000246 R12:
0000000000000009
[ 168.582796] R13: 0000000000000001 R14: 00007fac74be55e0 R15:
00007fac74be08c0
[ 168.583757] </TASK>
[ 168.584063] Modules linked in:
[ 168.584494] CR2: 0000000000000008
[ 168.584964] ---[ end trace 2475611ad0f77a1a ]---
This is because blkg_alloc() is called from blkg_conf_prep() without
holding 'q->queue_lock', and elevator is exited before blkg_create():
thread 1 thread 2
blkg_conf_prep
spin_lock_irq(&q->queue_lock);
blkg_lookup_check -> return NULL
spin_unlock_irq(&q->queue_lock);
blkg_alloc
blkcg_policy_enabled -> true
pd = ->pd_alloc_fn
blkg->pd[i] = pd
blk_mq_exit_sched
bfq_exit_queue
blkcg_deactivate_policy
spin_lock_irq(&q->queue_lock);
__clear_bit(pol->plid,
q->blkcg_pols);
spin_unlock_irq(&q->queue_lock);
q->elevator = NULL;
spin_lock_irq(&q->queue_lock);
blkg_create
if (blkg->pd[i])
->pd_init_fn -> q->elevator is NULL
spin_unlock_irq(&q->queue_lock);
Because blkcg_deactivate_policy() requires queue to be frozen, we can
grab q_usage_counter to synchoronize blkg_conf_prep() against
blkcg_deactivate_policy().
Fixes: e21b7a0b9887 ("block, bfq: add full hierarchical scheduling and
cgroups support")
Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
Acked-by: Tejun Heo <tj@xxxxxxxxxx>
