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() can take a long time if there are too
many blkgs in q->blkg_list, fix the problem by adding a mutex in q
and using it to synchoronize blkg creation against policy deactivation.
Fixes: e21b7a0b9887 ("block, bfq: add full hierarchical scheduling and cgroups support")
Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
---
Changes in V2:
- rename the patch title
- instead of checking policy in blkg_create(), using a new solution.
block/blk-cgroup.c | 7 +++++++
block/blk-core.c | 1 +
include/linux/blkdev.h | 5 +++++
3 files changed, 13 insertions(+)
diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index eb48090eefce..043f85a1e05e 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -621,6 +621,7 @@ struct block_device *blkcg_conf_open_bdev(char **inputp)
*/
int blkg_conf_prep(struct blkcg *blkcg, const struct blkcg_policy *pol,
char *input, struct blkg_conf_ctx *ctx)
+ __acquires(&bdev->bd_disk->queue->blkg_lock)
__acquires(rcu) __acquires(&bdev->bd_disk->queue->queue_lock)
{
struct block_device *bdev;
@@ -634,6 +635,7 @@ int blkg_conf_prep(struct blkcg *blkcg, const struct blkcg_policy *pol,
q = bdev->bd_disk->queue;
+ mutex_lock(&q->blkg_lock);
rcu_read_lock();
spin_lock_irq(&q->queue_lock);
@@ -713,6 +715,7 @@ int blkg_conf_prep(struct blkcg *blkcg, const struct blkcg_policy *pol,
fail_unlock:
spin_unlock_irq(&q->queue_lock);
rcu_read_unlock();
+ mutex_unlock(&q->blkg_lock);
fail:
blkdev_put_no_open(bdev);
/*
@@ -738,9 +741,11 @@ EXPORT_SYMBOL_GPL(blkg_conf_prep);
*/
void blkg_conf_finish(struct blkg_conf_ctx *ctx)
__releases(&ctx->bdev->bd_disk->queue->queue_lock) __releases(rcu)
+ __releases(&ctx->bdev->bd_disk->queue->blkg_lock)
{
spin_unlock_irq(&ctx->bdev->bd_disk->queue->queue_lock);
rcu_read_unlock();
+ mutex_unlock(&ctx->bdev->bd_disk->queue->blkg_lock);
blkdev_put_no_open(ctx->bdev);
}
EXPORT_SYMBOL_GPL(blkg_conf_finish);
@@ -1401,6 +1406,7 @@ void blkcg_deactivate_policy(struct request_queue *q,
if (queue_is_mq(q))
blk_mq_freeze_queue(q);
+ mutex_lock(&q->blkg_lock);
spin_lock_irq(&q->queue_lock);
__clear_bit(pol->plid, q->blkcg_pols);
@@ -1419,6 +1425,7 @@ void blkcg_deactivate_policy(struct request_queue *q,
}
spin_unlock_irq(&q->queue_lock);
+ mutex_unlock(&q->blkg_lock);
if (queue_is_mq(q))
blk_mq_unfreeze_queue(q);
diff --git a/block/blk-core.c b/block/blk-core.c
index d83e56b2f64e..f37fc03b1113 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -544,6 +544,7 @@ struct request_queue *blk_alloc_queue(int node_id)
INIT_LIST_HEAD(&q->icq_list);
#ifdef CONFIG_BLK_CGROUP
INIT_LIST_HEAD(&q->blkg_list);
+ mutex_init(&q->blkg_lock);
#endif
kobject_init(&q->kobj, &blk_queue_ktype);
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index b19172db7eef..c2d5be0f5f37 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -245,6 +245,11 @@ struct request_queue {
DECLARE_BITMAP (blkcg_pols, BLKCG_MAX_POLS);
struct blkcg_gq *root_blkg;
struct list_head blkg_list;
+ /*
+ * used to synchronize blkg allocation and initialization against
+ * policy deactivation.
+ */
+ struct mutex blkg_lock;
#endif
struct queue_limits limits;
--
2.31.1
