From: Yu Kuai yukuai3@huawei.com
[ Upstream commit 0c9d338c8443b06da8e8d3bfce824c5ea6d3488f ]
Our test reports 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@huawei.com Acked-by: Tejun Heo tj@kernel.org Link: https://lore.kernel.org/r/20211020014036.2141723-1-yukuai3@huawei.com Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Sasha Levin sashal@kernel.org --- block/blk-cgroup.c | 10 ++++++++++ 1 file changed, 10 insertions(+)
diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c index 9a1c5839dd469..ebff1af402e5b 100644 --- a/block/blk-cgroup.c +++ b/block/blk-cgroup.c @@ -633,6 +633,14 @@ int blkg_conf_prep(struct blkcg *blkcg, const struct blkcg_policy *pol,
q = bdev->bd_disk->queue;
+ /* + * blkcg_deactivate_policy() requires queue to be frozen, we can grab + * q_usage_counter to prevent concurrent with blkcg_deactivate_policy(). + */ + ret = blk_queue_enter(q, 0); + if (ret) + return ret; + rcu_read_lock(); spin_lock_irq(&q->queue_lock);
@@ -702,6 +710,7 @@ int blkg_conf_prep(struct blkcg *blkcg, const struct blkcg_policy *pol, goto success; } success: + blk_queue_exit(q); ctx->bdev = bdev; ctx->blkg = blkg; ctx->body = input; @@ -714,6 +723,7 @@ fail_unlock: rcu_read_unlock(); fail: blkdev_put_no_open(bdev); + blk_queue_exit(q); /* * If queue was bypassing, we should retry. Do so after a * short msleep(). It isn't strictly necessary but queue