linux-kernel - Re: [dm-devel] [PATCH] dm: remove unnecessary check when using dm_get

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Date:   Wed, 18 Jan 2023 21:16:41 +0800
From:   Hou Tao <houtao1@...wei.com>
To:     Hou Tao <houtao@...weicloud.com>, <dm-devel@...hat.com>
CC:     Mike Snitzer <snitzer@...nel.org>, <linux-kernel@...r.kernel.org>,
        Alasdair Kergon <agk@...hat.com>
Subject: Re: [dm-devel] [PATCH] dm: remove unnecessary check when using
 dm_get_mdptr()

ping ?

On 12/16/2022 12:23 PM, Hou Tao wrote:
> From: Hou Tao <houtao1@...wei.com>
>
> __hash_remove() removes hash_cell with _hash_lock locked, so acquiring
> _hash_lock can guarantee no-NULL hc returned from dm_get_mdptr() must
> have not been removed and hc->md must still be md.
>
> __hash_remove() also acquires dm_hash_cells_mutex before setting mdptr
> as NULL, so in dm_copy_name_and_uuid() after acquiring
> dm_hash_cells_mutex and ensuring returned hc is not NULL, the returned
> hc must still be alive and hc->md must still be md.
>
> So removing these unnecessary hc->md != md checks when using
> dm_get_mdptr() with _hash_lock or dm_hash_cells_mutex acquired.
>
> Signed-off-by: Hou Tao <houtao1@...wei.com>
> ---
>  drivers/md/dm-ioctl.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c
> index 3bfc1583c20a..2a86524661d1 100644
> --- a/drivers/md/dm-ioctl.c
> +++ b/drivers/md/dm-ioctl.c
> @@ -772,7 +772,7 @@ static struct dm_table *dm_get_inactive_table(struct mapped_device *md, int *src
>  
>  	down_read(&_hash_lock);
>  	hc = dm_get_mdptr(md);
> -	if (!hc || hc->md != md) {
> +	if (!hc) {
>  		DMERR("device has been removed from the dev hash table.");
>  		goto out;
>  	}
> @@ -1476,7 +1476,7 @@ static int table_load(struct file *filp, struct dm_ioctl *param, size_t param_si
>  	/* stage inactive table */
>  	down_write(&_hash_lock);
>  	hc = dm_get_mdptr(md);
> -	if (!hc || hc->md != md) {
> +	if (!hc) {
>  		DMERR("device has been removed from the dev hash table.");
>  		up_write(&_hash_lock);
>  		r = -ENXIO;
> @@ -2128,7 +2128,7 @@ int dm_copy_name_and_uuid(struct mapped_device *md, char *name, char *uuid)
>  
>  	mutex_lock(&dm_hash_cells_mutex);
>  	hc = dm_get_mdptr(md);
> -	if (!hc || hc->md != md) {
> +	if (!hc) {
>  		r = -ENXIO;
>  		goto out;
>  	}