Re: [PATCH v2 2/3] md/raid1,raid10: fix error-path detection with md_cloned_bio()

["Yu Kuai" <yukuai@fnnas.com>]

Hi,

在 2026/5/1 19:46, Abd-Alrhman Masalkhi 写道:
> Detect the error path using md_cloned_bio() instead of relying
> on r1_bio in raid1 or r10_bio->read_slot in raid10, which may be
> NULL or -1 after splitting and resubmitting a failed bio.
>
> As a result, the error path may not be recognized and memory
> allocations can incorrectly use GFP_NOIO instead of
> (GFP_NOIO | __GFP_HIGH), which can lead to a deadlock under
> memory pressure.

I don't think this patch will fix this problem. Because split bio
is a new bio that will be resubmit by md_submit_bio(), such bio is
not a md_cloned_bio yet until md_account_bio().

>
> Fixes: 689389a06ce7 ("md/raid1: simplify handle_read_error().")
> Fixes: 545250f24809 ("md/raid10: simplify handle_read_error()")
> Signed-off-by: Abd-Alrhman Masalkhi <abd.masalkhi@gmail.com>
> ---
> This patch depends on patch 1.
>
> Changes in v2:
>   - New patch.
> ---
>   drivers/md/raid1.c  | 13 ++++++++++---
>   drivers/md/raid10.c | 20 ++++++++++++++------
>   2 files changed, 24 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
> index cc9914bd15c1..c52ecd38c163 100644
> --- a/drivers/md/raid1.c
> +++ b/drivers/md/raid1.c
> @@ -1321,11 +1321,18 @@ static void raid1_read_request(struct mddev *mddev, struct bio *bio,
>   	bool r1bio_existed = !!r1_bio;
>   
>   	/*
> -	 * If r1_bio is set, we are blocking the raid1d thread
> -	 * so there is a tiny risk of deadlock.  So ask for
> +	 * An md cloned bio indicates we are in the error path.
> +	 * This is more reliable than checking r1_bio, which might
> +	 * be NULL even in the error path if a failed bio was split.
> +	 */
> +	bool err_path = md_cloned_bio(mddev, bio);
> +
> +	/*
> +	 * If we are in the error path, we are blocking the raid1d
> +	 * thread so there is a tiny risk of deadlock.  So ask for
>   	 * emergency memory if needed.
>   	 */
> -	gfp_t gfp = r1_bio ? (GFP_NOIO | __GFP_HIGH) : GFP_NOIO;
> +	gfp_t gfp = err_path ? (GFP_NOIO | __GFP_HIGH) : GFP_NOIO;
>   
>   	/*
>   	 * Still need barrier for READ in case that whole
> diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
> index 3a591e60a144..8c6fc398260e 100644
> --- a/drivers/md/raid10.c
> +++ b/drivers/md/raid10.c
> @@ -1155,7 +1155,20 @@ static void raid10_read_request(struct mddev *mddev, struct bio *bio,
>   	char b[BDEVNAME_SIZE];
>   	int slot = r10_bio->read_slot;
>   	struct md_rdev *err_rdev = NULL;
> -	gfp_t gfp = GFP_NOIO;
> +
> +	/*
> +	 * An md cloned bio indicates we are in the error path.
> +	 * This is more reliable than checking slot, which might
> +	 * be -1 even in the error path if a failed bio was split.
> +	 */
> +	bool err_path = md_cloned_bio(mddev, bio);
> +
> +	/*
> +	 * If we are in the error path, we are blocking the raid10d
> +	 * thread so there is a tiny risk of deadlock.  So ask for
> +	 * emergency memory if needed.
> +	 */
> +	gfp_t gfp = err_path ? (GFP_NOIO | __GFP_HIGH) : GFP_NOIO;
>   
>   	if (slot >= 0 && r10_bio->devs[slot].rdev) {
>   		/*
> @@ -1166,11 +1179,6 @@ static void raid10_read_request(struct mddev *mddev, struct bio *bio,
>   		 * we lose the device name in error messages.
>   		 */
>   		int disk;
> -		/*
> -		 * As we are blocking raid10, it is a little safer to
> -		 * use __GFP_HIGH.
> -		 */
> -		gfp = GFP_NOIO | __GFP_HIGH;
>   
>   		disk = r10_bio->devs[slot].devnum;
>   		err_rdev = conf->mirrors[disk].rdev;

-- 
Thansk,
Kuai