linux-kernel - Re: [PATCH 6.6.y v2 1/1] block: Fix bounce check logic in blk_queue_may

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Message-ID: <2025072551-tingling-botany-f00d@gregkh>
Date: Fri, 25 Jul 2025 14:04:01 +0200
From: Greg KH <gregkh@...uxfoundation.org>
To: Hardeep Sharma <quic_hardshar@...cinc.com>
Cc: Jens Axboe <axboe@...nel.dk>, Hannes Reinecke <hare@...e.de>,
	"Martin K . Petersen" <martin.petersen@...cle.com>,
	linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Subject: Re: [PATCH 6.6.y v2 1/1] block: Fix bounce check logic in
 blk_queue_may_bounce()

On Fri, Jul 25, 2025 at 04:57:10PM +0530, Hardeep Sharma wrote:
> Buffer bouncing is needed only when memory exists above the lowmem region,
> i.e., when max_low_pfn < max_pfn. The previous check (max_low_pfn >=
> max_pfn) was inverted and prevented bouncing when it could actually be
> required.
> 
> Note that bouncing depends on CONFIG_HIGHMEM, which is typically enabled
> on 32-bit ARM where not all memory is permanently mapped into the kernel’s
> lowmem region.
> 
> Fixes: 9bb33f24abbd0 ("block: refactor the bounce buffering code")
> Cc: stable@...r.kernel.org
> Signed-off-by: Hardeep Sharma <quic_hardshar@...cinc.com>
> ---
> Changelog v1..v2:
> 
> * Updated subject line
> 
>  block/blk.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/block/blk.h b/block/blk.h
> index 67915b04b3c1..f8a1d64be5a2 100644
> --- a/block/blk.h
> +++ b/block/blk.h
> @@ -383,7 +383,7 @@ static inline bool blk_queue_may_bounce(struct request_queue *q)
>  {
>  	return IS_ENABLED(CONFIG_BOUNCE) &&
>  		q->limits.bounce == BLK_BOUNCE_HIGH &&
> -		max_low_pfn >= max_pfn;
> +		max_low_pfn < max_pfn;
>  }
>  
>  static inline struct bio *blk_queue_bounce(struct bio *bio,
> -- 
> 2.25.1
> 
> 

<formletter>

This is not the correct way to submit patches for inclusion in the
stable kernel tree.  Please read:
    https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
for how to do this properly.

</formletter>