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

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Message-ID: <fff0529b-435c-ebea-9e18-c9df74591b55@huaweicloud.com>
Date:   Fri, 17 Feb 2023 19:49:45 +0800
From:   Hou Tao <houtao@...weicloud.com>
To:     dm-devel@...hat.com, Mike Snitzer <snitzer@...nel.org>
Cc:     linux-kernel@...r.kernel.org, Alasdair Kergon <agk@...hat.com>,
        "houtao1@...wei.com" <houtao1@...wei.com>
Subject: Re: [dm-devel] [PATCH] dm: remove unnecessary check when using
 dm_get_mdptr()

ping ? Any comments on this clean up patch ?

On 1/31/2023 9:44 AM, Hou Tao wrote:
> ping ? Any comments on this clean up patch ?
>
> On 1/18/2023 9:16 PM, Hou Tao wrote:
>> 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;
>>>  	}
> .