Re: [PATCH] block/mq-deadline: Fix WARN when set async_depth by sysfs

[Damien Le Moal]

On 3/29/24 11:44, Zhiguo Niu wrote:
> A WARN may occur when async_depth is set from user by sysfs,
> the warning log is as following:
> 
> [  623.848659] WARNING: CPU: 0 PID: 7798 at lib/sbitmap.c:537 sbitmap_queue_get_shallow+0x2c/0x38
> [  623.878550] CPU: 0 PID: 7798 Comm: kworker/u16:2 Tainted: G        W  OE      6.6.0-mainline-g8d9254e6f4a0-dirty-ab000013 #1
> [  623.880091] Hardware name: Unisoc UMS9621-base Board (DT)
> [  623.880906] Workqueue: writeback wb_workfn (flush-254:48)
> [  623.881748] pstate: 20400005 (nzCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
> [  623.882763] pc : sbitmap_queue_get_shallow+0x2c/0x38
> [  623.883525] lr : __blk_mq_get_tag+0x50/0xd4
> [  623.884198] sp : ffffffc08a073230
> [  623.884745] x29: ffffffc08a073230 x28: ffffffc0821445e0 x27: 0000000000000000
> [  623.885799] x26: ffffff8087de8000 x25: 0000000000000000 x24: 0000000000000002
> [  623.886849] x23: ffffffc0820f2008 x22: ffffff8088ac3918 x21: ffffff808c358f10
> [  623.887897] x20: ffffff808c358f00 x19: ffffffc08a073360 x18: ffffffc08bde70a8
> [  623.888946] x17: 000000007e57c819 x16: 000000007e57c819 x15: fffffffdfe000000
> [  623.889993] x14: 0000000000000001 x13: 0000000000000004 x12: 00000003c6c931ed
> [  623.891038] x11: ffffff80939a3800 x10: ffffffc0801ac88c x9 : 0000000000000000
> [  623.892086] x8 : 0000000000000006 x7 : 0000000000000000 x6 : ffffffc080765204
> [  623.893131] x5 : 0000000000000000 x4 : 0000000000000001 x3 : 0000000000000000
> [  623.894174] x2 : ffffffc080765224 x1 : 0000000000000005 x0 : ffffff808c358f10
> [  623.895221] Call trace:
> [  623.895660] sbitmap_queue_get_shallow+0x2c/0x38
> [  623.896379] blk_mq_get_tag+0xa0/0x350
> [  623.896992] __blk_mq_alloc_requests+0x218/0x300
> [  623.897715] blk_mq_submit_bio+0x314/0x774
> [  623.898369] __submit_bio+0xb4/0xe0
> [  623.898950] submit_bio_noacct_nocheck+0x110/0x324
> [  623.899692] submit_bio_noacct+0x278/0x3f8
> [  623.900344] submit_bio+0xcc/0xe8
> [  623.900900] f2fs_submit_write_bio+0x100/0x428
> [  623.901605] __submit_merged_bio+0x74/0x1ac
> [  623.902269] __submit_merged_write_cond+0x188/0x1f4
> [  623.903022] f2fs_write_data_pages+0xb10/0xc2c
> [  623.903727] do_writepages+0xf4/0x618
> [  623.904332] __writeback_single_inode+0x78/0x60c
> [  623.905055] writeback_sb_inodes+0x294/0x520
> [  623.905734] __writeback_inodes_wb+0xa0/0xf4
> [  623.906413] wb_writeback+0x188/0x4e8
> [  623.907014] wb_workfn+0x420/0x608
> [  623.907582] process_one_work+0x23c/0x55c
> [  623.908227] worker_thread+0x2ac/0x3e4
> [  623.908838] kthread+0x108/0x12c
> [  623.909389] ret_from_fork+0x10/0x20
> 
> The rootcause is user may set async_depth to a value which is less
> than its initial value from dd_init_hctx->dd_depth_updated, and this
> initial value is set to sbq->min_shallow_depth, when async_depth is
> modified by user from sysfs, sbq->min_shallow_depth will not be changed
> simultaneously, and it is also not easy to obtain tag sbitmap information
> in deadline_async_depth_store.
> 
> So a suitable value should be set to min_shallow_depth in dd_depth_updated.
> 
> Signed-off-by: Zhiguo Niu <zhiguo.niu@xxxxxxxxxx>
> ---
>  block/mq-deadline.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/block/mq-deadline.c b/block/mq-deadline.c
> index 02a916b..89c516e 100644
> --- a/block/mq-deadline.c
> +++ b/block/mq-deadline.c
> @@ -646,10 +646,12 @@ static void dd_depth_updated(struct blk_mq_hw_ctx *hctx)
>  	struct request_queue *q = hctx->queue;
>  	struct deadline_data *dd = q->elevator->elevator_data;
>  	struct blk_mq_tags *tags = hctx->sched_tags;
> +	unsigned int shift = tags->bitmap_tags.sb.shift;
> +	unsigned int dd_min_depth = max(1U, 3 * (1U << shift)  / 4);

Extra blank space before "/".
That division could also be replaced with ">> 2".

>  
>  	dd->async_depth = max(1UL, 3 * q->nr_requests / 4);
>  
> -	sbitmap_queue_min_shallow_depth(&tags->bitmap_tags, dd->async_depth);
> +	sbitmap_queue_min_shallow_depth(&tags->bitmap_tags, dd_min_depth);
>  }
>  
>  /* Called by blk_mq_init_hctx() and blk_mq_init_sched(). */

-- 
Damien Le Moal
Western Digital Research