* [PATCH] blk-cgroup: Remove unnecessary rcu_read_lock/unlock()
@ 2022-05-16 17:39 bh1scw
2022-05-16 18:42 ` Tejun Heo
` (3 more replies)
0 siblings, 4 replies; 7+ messages in thread
From: bh1scw @ 2022-05-16 17:39 UTC (permalink / raw)
To: tj, axboe; +Cc: cgroups, linux-block, linux-kernel, songmuchun, Fanjun Kong
From: Fanjun Kong <bh1scw@gmail.com>
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@gmail.com>
---
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);
--
2.36.0
^ permalink raw reply related [flat|nested] 7+ messages in thread
* Re: [PATCH] blk-cgroup: Remove unnecessary rcu_read_lock/unlock()
2022-05-16 17:39 [PATCH] blk-cgroup: Remove unnecessary rcu_read_lock/unlock() bh1scw
@ 2022-05-16 18:42 ` Tejun Heo
2022-05-17 4:11 ` Muchun Song
` (2 subsequent siblings)
3 siblings, 0 replies; 7+ messages in thread
From: Tejun Heo @ 2022-05-16 18:42 UTC (permalink / raw)
To: bh1scw; +Cc: axboe, cgroups, linux-block, linux-kernel, songmuchun
On Tue, May 17, 2022 at 01:39:30AM +0800, bh1scw@gmail.com wrote:
> From: Fanjun Kong <bh1scw@gmail.com>
>
> 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@gmail.com>
Acked-by: Tejun Heo <tj@kernel.org>
Thanks.
--
tejun
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] blk-cgroup: Remove unnecessary rcu_read_lock/unlock()
2022-05-16 17:39 [PATCH] blk-cgroup: Remove unnecessary rcu_read_lock/unlock() bh1scw
2022-05-16 18:42 ` Tejun Heo
@ 2022-05-17 4:11 ` Muchun Song
2022-05-17 12:13 ` Jens Axboe
[not found] ` <CGME20220518192850eucas1p1458c00d4917c5ed39f2c37c9eb30cd46@eucas1p1.samsung.com>
3 siblings, 0 replies; 7+ messages in thread
From: Muchun Song @ 2022-05-17 4:11 UTC (permalink / raw)
To: bh1scw; +Cc: Tejun Heo, Jens Axboe, Cgroups, open list:BLOCK LAYER, LKML
On Tue, May 17, 2022 at 1:39 AM <bh1scw@gmail.com> wrote:
>
> From: Fanjun Kong <bh1scw@gmail.com>
>
> 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@gmail.com>
Reviewed-by: Muchun Song <songmuchun@bytedance.com>
Thanks.
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] blk-cgroup: Remove unnecessary rcu_read_lock/unlock()
2022-05-16 17:39 [PATCH] blk-cgroup: Remove unnecessary rcu_read_lock/unlock() bh1scw
2022-05-16 18:42 ` Tejun Heo
2022-05-17 4:11 ` Muchun Song
@ 2022-05-17 12:13 ` Jens Axboe
[not found] ` <CGME20220518192850eucas1p1458c00d4917c5ed39f2c37c9eb30cd46@eucas1p1.samsung.com>
3 siblings, 0 replies; 7+ messages in thread
From: Jens Axboe @ 2022-05-17 12:13 UTC (permalink / raw)
To: tj, bh1scw; +Cc: songmuchun, linux-block, cgroups, linux-kernel
On Tue, 17 May 2022 01:39:30 +0800, bh1scw@gmail.com wrote:
> From: Fanjun Kong <bh1scw@gmail.com>
>
> 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().
>
>
> [...]
Applied, thanks!
[1/1] blk-cgroup: Remove unnecessary rcu_read_lock/unlock()
commit: 77c570a1ea85ba4ab135c61a028420a6e9fe77f3
Best regards,
--
Jens Axboe
^ permalink raw reply [flat|nested] 7+ messages in thread
[parent not found: <CGME20220518192850eucas1p1458c00d4917c5ed39f2c37c9eb30cd46@eucas1p1.samsung.com>]
* Re: [PATCH] blk-cgroup: Remove unnecessary rcu_read_lock/unlock()
[not found] ` <CGME20220518192850eucas1p1458c00d4917c5ed39f2c37c9eb30cd46@eucas1p1.samsung.com>
@ 2022-05-18 19:28 ` Marek Szyprowski
2022-05-18 22:29 ` Jens Axboe
0 siblings, 1 reply; 7+ messages in thread
From: Marek Szyprowski @ 2022-05-18 19:28 UTC (permalink / raw)
To: bh1scw, tj, axboe; +Cc: cgroups, linux-block, linux-kernel, songmuchun
On 16.05.2022 19:39, bh1scw@gmail.com wrote:
> From: Fanjun Kong <bh1scw@gmail.com>
>
> 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@gmail.com>
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
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] blk-cgroup: Remove unnecessary rcu_read_lock/unlock()
2022-05-18 19:28 ` Marek Szyprowski
@ 2022-05-18 22:29 ` Jens Axboe
2022-05-18 22:31 ` Jens Axboe
0 siblings, 1 reply; 7+ messages in thread
From: Jens Axboe @ 2022-05-18 22:29 UTC (permalink / raw)
To: Marek Szyprowski, bh1scw, tj
Cc: cgroups, linux-block, linux-kernel, songmuchun
On 5/18/22 1:28 PM, Marek Szyprowski wrote:
> On 16.05.2022 19:39, bh1scw@gmail.com wrote:
>> From: Fanjun Kong <bh1scw@gmail.com>
>>
>> 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@gmail.com>
>
> 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
Should this use rcu_read_lock_any_held() rather than rcu_read_lock_held()?
--
Jens Axboe
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] blk-cgroup: Remove unnecessary rcu_read_lock/unlock()
2022-05-18 22:29 ` Jens Axboe
@ 2022-05-18 22:31 ` Jens Axboe
0 siblings, 0 replies; 7+ messages in thread
From: Jens Axboe @ 2022-05-18 22:31 UTC (permalink / raw)
To: Marek Szyprowski, bh1scw, tj
Cc: cgroups, linux-block, linux-kernel, songmuchun
On 5/18/22 4:29 PM, Jens Axboe wrote:
> On 5/18/22 1:28 PM, Marek Szyprowski wrote:
>> On 16.05.2022 19:39, bh1scw@gmail.com wrote:
>>> From: Fanjun Kong <bh1scw@gmail.com>
>>>
>>> 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@gmail.com>
>>
>> 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
>
> Should this use rcu_read_lock_any_held() rather than
> rcu_read_lock_held()?
I think the better alternative is just to delete the WARN_ON(), we have
a:
lockdep_assert_held(&q->queue_lock);
right after it. Since the queue_lock is IRQ disabling, having two checks
serves no purpose. I'll kill the line.
--
Jens Axboe
^ permalink raw reply [flat|nested] 7+ messages in thread
end of thread, other threads:[~2022-05-18 22:32 UTC | newest]
Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed)
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2022-05-16 17:39 [PATCH] blk-cgroup: Remove unnecessary rcu_read_lock/unlock() bh1scw
2022-05-16 18:42 ` Tejun Heo
2022-05-17 4:11 ` Muchun Song
2022-05-17 12:13 ` Jens Axboe
[not found] ` <CGME20220518192850eucas1p1458c00d4917c5ed39f2c37c9eb30cd46@eucas1p1.samsung.com>
2022-05-18 19:28 ` Marek Szyprowski
2022-05-18 22:29 ` Jens Axboe
2022-05-18 22:31 ` Jens Axboe
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