linux-kernel - Re: [PATCH md-6.12 4/7] md/raid1: factor out helper to handle blocked rdev from raid1_write

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Message-ID: <20240830130645.000076c6@linux.intel.com>
Date: Fri, 30 Aug 2024 13:06:45 +0200
From: Mariusz Tkaczyk <mariusz.tkaczyk@...ux.intel.com>
To: Yu Kuai <yukuai1@...weicloud.com>
Cc: mariusz.tkaczyk@...el.com, song@...nel.org, linux-raid@...r.kernel.org,
 linux-kernel@...r.kernel.org, yukuai3@...wei.com, yi.zhang@...wei.com,
 yangerkun@...wei.com
Subject: Re: [PATCH md-6.12 4/7] md/raid1: factor out helper to handle
 blocked rdev from raid1_write_request()

On Fri, 30 Aug 2024 15:27:18 +0800
Yu Kuai <yukuai1@...weicloud.com> wrote:

> From: Yu Kuai <yukuai3@...wei.com>
> 
> Currently raid1 is preparing IO for underlying disks while checking if
> any disk is blocked, if so allocated resources must be released, then
> waiting for rdev to be unblocked and try to prepare IO again.
> 
> Make code cleaner by checking blocked rdev first, it doesn't matter if
> rdev is blocked while issuing this IO.
> 
> Signed-off-by: Yu Kuai <yukuai3@...wei.com>
> ---
>  drivers/md/raid1.c | 84 ++++++++++++++++++++++++++--------------------
>  1 file changed, 48 insertions(+), 36 deletions(-)
> 
> diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
> index f55c8e67d059..aa30c3240c85 100644
> --- a/drivers/md/raid1.c
> +++ b/drivers/md/raid1.c
> @@ -1406,6 +1406,49 @@ static void raid1_read_request(struct mddev *mddev,
> struct bio *bio, submit_bio_noacct(read_bio);
>  }
>  
> +static bool wait_blocked_rdev(struct mddev *mddev, struct bio *bio)
> +{
> +	struct r1conf *conf = mddev->private;
> +	int disks = conf->raid_disks * 2;
> +	int i;
> +
> +retry:
> +	for (i = 0; i < disks; i++) {
> +		struct md_rdev *rdev = conf->mirrors[i].rdev;
> +
> +		if (!rdev)
> +			continue;
> +
> +		if (test_bit(Blocked, &rdev->flags)) {
Don't we need unlikely here?


> +			if (bio->bi_opf & REQ_NOWAIT)
> +				return false;
> +
> +			mddev_add_trace_msg(rdev->mddev, "raid1 wait rdev %d
> blocked",
> +					    rdev->raid_disk);
> +			atomic_inc(&rdev->nr_pending);


retry moves us before for (ugh, ugly) and "theoretically" we can back here
with the same disk and increase nr_pending twice or more because rdve can become
block again from different thread.

This is what I suspect but it could be wrong.

Mariusz