On 16.05.2022 19:39, bh1scw@xxxxxxxxx wrote:
> From: Fanjun Kong <bh1scw@xxxxxxxxx>
>
> spin_lock_irq/spin_unlock_irq contains preempt_disable/enable().
> Which can serve as RCU read-side critical region, so remove
> rcu_read_lock/unlock().
>
> Signed-off-by: Fanjun Kong <bh1scw@xxxxxxxxx>
This patch landed in today's linux next-20220518 as commit 77c570a1ea85
("blk-cgroup: Remove unnecessary rcu_read_lock/unlock()").
Unfortunately it triggers the following warning on ARM64 based Raspberry
Pi 4B board:
------------[ cut here ]------------
WARNING: CPU: 0 PID: 1 at block/blk-cgroup.c:301 blkg_create+0x398/0x4e0
Modules linked in:
CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.18.0-rc3+ #5080
Hardware name: Raspberry Pi 4 Model B (DT)
pstate: 600000c5 (nZCv daIF -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
pc : blkg_create+0x398/0x4e0
...
Call trace:
blkg_create+0x398/0x4e0
blkcg_init_queue+0x74/0x204
__alloc_disk_node+0xf8/0x1f0
__blk_alloc_disk+0x38/0x140
brd_alloc.part.0+0xf8/0x220
brd_init+0xe8/0x164
do_one_initcall+0x74/0x400
kernel_init_freeable+0x2f4/0x37c
kernel_init+0x28/0x130
ret_from_fork+0x10/0x20
irq event stamp: 218372
hardirqs last enabled at (218371): [<ffff80000914b99c>]
_raw_spin_unlock_irqrestore+0x98/0x9c
hardirqs last disabled at (218372): [<ffff80000914bcbc>]
_raw_spin_lock_irq+0xac/0xb0
softirqs last enabled at (216732): [<ffff800008010470>] _stext+0x470/0x5e8
softirqs last disabled at (216723): [<ffff8000080a0ec4>]
__irq_exit_rcu+0x180/0x1ac
---[ end trace 0000000000000000 ]---
If this is a false positive, then the check in the code needs to be
adjusted.
> ---
> block/blk-cgroup.c | 4 +---
> 1 file changed, 1 insertion(+), 3 deletions(-)
>
> diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
> index a91f8ae18b49..7bdc16a36560 100644
> --- a/block/blk-cgroup.c
> +++ b/block/blk-cgroup.c
> @@ -1283,14 +1283,13 @@ int blkcg_init_queue(struct request_queue *q)
> preloaded = !radix_tree_preload(GFP_KERNEL);
>
> /* Make sure the root blkg exists. */
> - rcu_read_lock();
> + /* spin_lock_irq can serve as RCU read-side critical section. */
> spin_lock_irq(&q->queue_lock);
> blkg = blkg_create(&blkcg_root, q, new_blkg);
> if (IS_ERR(blkg))
> goto err_unlock;
> q->root_blkg = blkg;
> spin_unlock_irq(&q->queue_lock);
> - rcu_read_unlock();
>
> if (preloaded)
> radix_tree_preload_end();
> @@ -1316,7 +1315,6 @@ int blkcg_init_queue(struct request_queue *q)
> return ret;
> err_unlock:
> spin_unlock_irq(&q->queue_lock);
> - rcu_read_unlock();
> if (preloaded)
> radix_tree_preload_end();
> return PTR_ERR(blkg);
Best regards
--
Marek Szyprowski, PhD
Samsung R&D Institute Poland
