linux-kernel - Re: [PATCH v2 01/12] md/raid5: Factor out ahead_of

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Date:   Thu, 21 Apr 2022 11:17:50 +0200
From:   Paul Menzel <pmenzel@...gen.mpg.de>
To:     Logan Gunthorpe <logang@...tatee.com>
Cc:     linux-kernel@...r.kernel.org, linux-raid@...r.kernel.org,
        Song Liu <song@...nel.org>,
        Christoph Hellwig <hch@...radead.org>,
        Guoqing Jiang <guoqing.jiang@...ux.dev>,
        Stephen Bates <sbates@...thlin.com>,
        Martin Oliveira <Martin.Oliveira@...eticom.com>,
        David Sloan <David.Sloan@...eticom.com>,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v2 01/12] md/raid5: Factor out ahead_of_reshape() function

Dear Logan,


Thank you for these patches.


Am 20.04.22 um 21:54 schrieb Logan Gunthorpe:
> There are a few uses of an ugly ternary operator in raid5_make_request()
> to check if a sector is a head of a reshape sector.
> 
> Factor this out into a simple helper called ahead_of_reshape().
> 
> This appears to fix the first bio_wouldblock_error() check which appears
> to have comparison operators that didn't match the check below which
> causes a schedule. Besides this, no functional changes intended.

If there is an error, could that be fixed in a separate commit, which 
could be applied to the stable series?

> Suggested-by: Christoph Hellwig <hch@....de>
> Signed-off-by: Logan Gunthorpe <logang@...tatee.com>
> ---
>   drivers/md/raid5.c | 29 +++++++++++++++++------------
>   1 file changed, 17 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
> index 7f7d1546b9ba..97b23c18402b 100644
> --- a/drivers/md/raid5.c
> +++ b/drivers/md/raid5.c
> @@ -5787,6 +5787,15 @@ static void make_discard_request(struct mddev *mddev, struct bio *bi)
>   	bio_endio(bi);
>   }
>   
> +static bool ahead_of_reshape(struct mddev *mddev, sector_t sector,
> +			     sector_t reshape_sector)
> +{
> +	if (mddev->reshape_backwards)
> +		return sector < reshape_sector;
> +	else
> +		return sector >= reshape_sector;

I like the ternary operator. ;-)

     return mddev->reshape_backwards ? (return sector < reshape_sector) 
: (sector >= reshape_sector)

Sorry, does not matter.

Reviewed-by: Paul Menzel <pmenzel@...gen.mpg.de>



Kind regards,

Paul


> +}
> +
>   static bool raid5_make_request(struct mddev *mddev, struct bio * bi)
>   {
>   	struct r5conf *conf = mddev->private;
> @@ -5843,9 +5852,8 @@ static bool raid5_make_request(struct mddev *mddev, struct bio * bi)
>   	/* Bail out if conflicts with reshape and REQ_NOWAIT is set */
>   	if ((bi->bi_opf & REQ_NOWAIT) &&
>   	    (conf->reshape_progress != MaxSector) &&
> -	    (mddev->reshape_backwards
> -	    ? (logical_sector > conf->reshape_progress && logical_sector <= conf->reshape_safe)
> -	    : (logical_sector >= conf->reshape_safe && logical_sector < conf->reshape_progress))) {
> +	    !ahead_of_reshape(mddev, logical_sector, conf->reshape_progress) &&
> +	    ahead_of_reshape(mddev, logical_sector, conf->reshape_safe)) {
>   		bio_wouldblock_error(bi);
>   		if (rw == WRITE)
>   			md_write_end(mddev);
> @@ -5874,14 +5882,12 @@ static bool raid5_make_request(struct mddev *mddev, struct bio * bi)
>   			 * to check again.
>   			 */
>   			spin_lock_irq(&conf->device_lock);
> -			if (mddev->reshape_backwards
> -			    ? logical_sector < conf->reshape_progress
> -			    : logical_sector >= conf->reshape_progress) {
> +			if (ahead_of_reshape(mddev, logical_sector,
> +					     conf->reshape_progress)) {
>   				previous = 1;
>   			} else {
> -				if (mddev->reshape_backwards
> -				    ? logical_sector < conf->reshape_safe
> -				    : logical_sector >= conf->reshape_safe) {
> +				if (ahead_of_reshape(mddev, logical_sector,
> +						     conf->reshape_safe)) {
>   					spin_unlock_irq(&conf->device_lock);
>   					schedule();
>   					do_prepare = true;
> @@ -5912,9 +5918,8 @@ static bool raid5_make_request(struct mddev *mddev, struct bio * bi)
>   				 */
>   				int must_retry = 0;
>   				spin_lock_irq(&conf->device_lock);
> -				if (mddev->reshape_backwards
> -				    ? logical_sector >= conf->reshape_progress
> -				    : logical_sector < conf->reshape_progress)
> +				if (!ahead_of_reshape(mddev, logical_sector,
> +						      conf->reshape_progress))
>   					/* mismatch, need to try again */
>   					must_retry = 1;
>   				spin_unlock_irq(&conf->device_lock);