From: Yu Kuai <yukuai3@huawei.com>

Queue is freezed while activating policy, allocate memory with queue
freezed has the risk of deadlock because memory reclaim can issue new
IO.

Signed-off-by: Yu Kuai <yukuai3@huawei.com>
---
 block/blk-cgroup.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 7246fc256315..0c7b58696d3c 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -1630,7 +1630,7 @@ int blkcg_activate_policy(struct gendisk *disk, const struct blkcg_policy *pol)
 		if (!pd) {
 			/*
 			 * GFP_NOWAIT failed.  Free the existing one and
-			 * prealloc for @blkg w/ GFP_KERNEL.
+			 * prealloc for @blkg w/ GFP_NOIO.
 			 */
 			if (pinned_blkg)
 				blkg_put(pinned_blkg);
@@ -1642,7 +1642,7 @@ int blkcg_activate_policy(struct gendisk *disk, const struct blkcg_policy *pol)
 			if (pd_prealloc)
 				pol->pd_free_fn(pd_prealloc);
 			pd_prealloc = pol->pd_alloc_fn(disk, blkg->blkcg,
-						       GFP_KERNEL);
+						       GFP_NOIO);
 			if (pd_prealloc)
 				goto retry;
 			else
-- 
2.39.2

On Tue, Sep 23, 2025 at 4:06 PM Yu Kuai <yukuai1@huaweicloud.com> wrote:
>
> From: Yu Kuai <yukuai3@huawei.com>
>
> Queue is freezed while activating policy, allocate memory with queue
> freezed has the risk of deadlock because memory reclaim can issue new
> IO.

blk_mq_freeze_queue() already covers it by calling memalloc_noio_save(),
so this patch looks not necessary.

Or do you have a lockdep warning?

Thanks,

Hi,

在 2025/09/23 19:03, Ming Lei 写道:
> On Tue, Sep 23, 2025 at 4:06 PM Yu Kuai <yukuai1@huaweicloud.com> wrote:
>>
>> From: Yu Kuai <yukuai3@huawei.com>
>>
>> Queue is freezed while activating policy, allocate memory with queue
>> freezed has the risk of deadlock because memory reclaim can issue new
>> IO.
> 
> blk_mq_freeze_queue() already covers it by calling memalloc_noio_save(),
> so this patch looks not necessary.
> 
Yes, this can just consider a cleanup, I'll remove this if we think this
is not necessary.

> Or do you have a lockdep warning?
> 

No.

Thanks,
Kuai

> Thanks,
> 
> 
> 
> .
>