[PATCH] dm-verity: use softirq context only when !need_resched()

[PATCH] dm-verity: use softirq context only when !need_resched()

[Eric Biggers]

From: Eric Biggers <ebiggers@google.com>

Further limit verification in softirq (a.k.a. BH) context to cases where
rescheduling of the interrupted task is not pending.

This helps prevent the CPU from spending too long in softirq context.

Note that handle_softirqs() in kernel/softirq.c already stops running
softirqs in this same case.  However, that check is too coarse-grained,
since many I/O requests can be processed in a single BLOCK_SOFTIRQ.

Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 drivers/md/dm-verity-target.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/md/dm-verity-target.c b/drivers/md/dm-verity-target.c
index 3c427f18a04b3..4de2c226ac9db 100644
--- a/drivers/md/dm-verity-target.c
+++ b/drivers/md/dm-verity-target.c
@@ -680,11 +680,12 @@ static void verity_bh_work(struct work_struct *w)
 }
 
 static inline bool verity_use_bh(unsigned int bytes, unsigned short ioprio)
 {
 	return ioprio <= IOPRIO_CLASS_IDLE &&
-		bytes <= READ_ONCE(dm_verity_use_bh_bytes[ioprio]);
+		bytes <= READ_ONCE(dm_verity_use_bh_bytes[ioprio]) &&
+		!need_resched();
 }
 
 static void verity_end_io(struct bio *bio)
 {
 	struct dm_verity_io *io = bio->bi_private;

base-commit: a33b5a08cbbdd7aadff95f40cbb45ab86841679e
-- 
2.49.0

Re: [PATCH] dm-verity: use softirq context only when !need_resched()

[Mikulas Patocka]

OK, Accepted.

Mikulas



On Tue, 22 Apr 2025, Eric Biggers wrote:

> From: Eric Biggers <ebiggers@google.com>
> 
> Further limit verification in softirq (a.k.a. BH) context to cases where
> rescheduling of the interrupted task is not pending.
> 
> This helps prevent the CPU from spending too long in softirq context.
> 
> Note that handle_softirqs() in kernel/softirq.c already stops running
> softirqs in this same case.  However, that check is too coarse-grained,
> since many I/O requests can be processed in a single BLOCK_SOFTIRQ.
> 
> Signed-off-by: Eric Biggers <ebiggers@google.com>
> ---
>  drivers/md/dm-verity-target.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/md/dm-verity-target.c b/drivers/md/dm-verity-target.c
> index 3c427f18a04b3..4de2c226ac9db 100644
> --- a/drivers/md/dm-verity-target.c
> +++ b/drivers/md/dm-verity-target.c
> @@ -680,11 +680,12 @@ static void verity_bh_work(struct work_struct *w)
>  }
>  
>  static inline bool verity_use_bh(unsigned int bytes, unsigned short ioprio)
>  {
>  	return ioprio <= IOPRIO_CLASS_IDLE &&
> -		bytes <= READ_ONCE(dm_verity_use_bh_bytes[ioprio]);
> +		bytes <= READ_ONCE(dm_verity_use_bh_bytes[ioprio]) &&
> +		!need_resched();
>  }
>  
>  static void verity_end_io(struct bio *bio)
>  {
>  	struct dm_verity_io *io = bio->bi_private;
> 
> base-commit: a33b5a08cbbdd7aadff95f40cbb45ab86841679e
> -- 
> 2.49.0
>