Re: [PATCH] btrfs: replace kcalloc() calls to kzalloc_objs()

[Qu Wenruo <wqu@suse.com>]

在 2026/2/24 17:06, Miquel Sabaté Solà 写道:
> Qu Wenruo @ 2026-02-24 15:07 +1030:
> 
>> 在 2026/2/24 10:14, Miquel Sabaté Solà 写道:
>>> Commit 2932ba8d9c99 ("slab: Introduce kmalloc_obj() and family")
>>> introduced, among many others, the kzalloc_objs() helper, which has some
>>> benefits over kcalloc().
>>> Cc: Kees Cook <kees@kernel.org>
>>> Signed-off-by: Miquel Sabaté Solà <mssola@mssola.com>
>>> ---
>>>    fs/btrfs/block-group.c       | 2 +-
>>>    fs/btrfs/raid56.c            | 8 ++++----
>>>    fs/btrfs/tests/zoned-tests.c | 2 +-
>>>    fs/btrfs/volumes.c           | 6 ++----
>>>    fs/btrfs/zoned.c             | 5 ++---
>>>    5 files changed, 10 insertions(+), 13 deletions(-)
>>> diff --git a/fs/btrfs/block-group.c b/fs/btrfs/block-group.c
>>> index 37bea850b3f0..8d85b4707690 100644
>>> --- a/fs/btrfs/block-group.c
>>> +++ b/fs/btrfs/block-group.c
>>> @@ -2239,7 +2239,7 @@ int btrfs_rmap_block(struct btrfs_fs_info *fs_info, u64 chunk_start,
>>>    	if (map->type & BTRFS_BLOCK_GROUP_RAID56_MASK)
>>>    		io_stripe_size = btrfs_stripe_nr_to_offset(nr_data_stripes(map));
>>>    -	buf = kcalloc(map->num_stripes, sizeof(u64), GFP_NOFS);
>>> +	buf = kzalloc_objs(*buf, map->num_stripes, GFP_NOFS);
>>
>> Not sure if we should use *buf for the type.
>>
>> I still remember we had some bugs related to incorrect type usage.
> 
> Considering the type of 'buf' and how kzalloc_objs() will resolve the
> first argument '*buf', it should really just be equivalent to what was
> written before.

Good luck if you miss the '*' for a structure pointer, and compiler 
won't give you any warning.

I still remembered that Johannes exposed such bug for me.
Unfortunately I didn't have exact lore link for it.

> 
>>
>> Another thing is, we may not want to use the kzalloc version.
>> We don't want to waste CPU time just to zero out the content meanwhile we're
>> ensured to re-assign the contents.
>>
>> Thus kmalloc_objs() maybe better.
> 
> Yes, having a second look at this function, it looks like kmalloc_objs()
> might just be enough. If you don't mind, I will add another commit in v2
> translating kzalloc_objs() into kmalloc_objs() wherever I see we can do
> this from the ones I've touched. This way we can easily revert in case
> things go south :)
> 
>>
>> Thanks,
>> Qu
> 
> Thanks,
> Miquel
> 
>>
>>
>>>    	if (!buf) {
>>>    		ret = -ENOMEM;
>>>    		goto out;
>>> diff --git a/fs/btrfs/raid56.c b/fs/btrfs/raid56.c
>>> index 02105d68accb..1ebfed8f0a0a 100644
>>> --- a/fs/btrfs/raid56.c
>>> +++ b/fs/btrfs/raid56.c
>>> @@ -2110,8 +2110,8 @@ static int recover_sectors(struct btrfs_raid_bio *rbio)
>>>    	 * @unmap_array stores copy of pointers that does not get reordered
>>>    	 * during reconstruction so that kunmap_local works.
>>>    	 */
>>> -	pointers = kcalloc(rbio->real_stripes, sizeof(void *), GFP_NOFS);
>>> -	unmap_array = kcalloc(rbio->real_stripes, sizeof(void *), GFP_NOFS);
>>> +	pointers = kzalloc_objs(*pointers, rbio->real_stripes, GFP_NOFS);
>>> +	unmap_array = kzalloc_objs(*unmap_array, rbio->real_stripes, GFP_NOFS);
>>>    	if (!pointers || !unmap_array) {
>>>    		ret = -ENOMEM;
>>>    		goto out;
>>> @@ -2844,8 +2844,8 @@ static int recover_scrub_rbio(struct btrfs_raid_bio *rbio)
>>>    	 * @unmap_array stores copy of pointers that does not get reordered
>>>    	 * during reconstruction so that kunmap_local works.
>>>    	 */
>>> -	pointers = kcalloc(rbio->real_stripes, sizeof(void *), GFP_NOFS);
>>> -	unmap_array = kcalloc(rbio->real_stripes, sizeof(void *), GFP_NOFS);
>>> +	pointers = kzalloc_objs(*pointers, rbio->real_stripes, GFP_NOFS);
>>> +	unmap_array = kzalloc_objs(*unmap_array, rbio->real_stripes, GFP_NOFS);
>>>    	if (!pointers || !unmap_array) {
>>>    		ret = -ENOMEM;
>>>    		goto out;
>>> diff --git a/fs/btrfs/tests/zoned-tests.c b/fs/btrfs/tests/zoned-tests.c
>>> index da21c7aea31a..2bc3b14baa41 100644
>>> --- a/fs/btrfs/tests/zoned-tests.c
>>> +++ b/fs/btrfs/tests/zoned-tests.c
>>> @@ -58,7 +58,7 @@ static int test_load_zone_info(struct btrfs_fs_info *fs_info,
>>>    		return -ENOMEM;
>>>    	}
>>>    -	zone_info = kcalloc(test->num_stripes, sizeof(*zone_info), GFP_KERNEL);
>>> +	zone_info = kzalloc_objs(*zone_info, test->num_stripes, GFP_KERNEL);
>>>    	if (!zone_info) {
>>>    		test_err("cannot allocate zone info");
>>>    		return -ENOMEM;
>>> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
>>> index e15e138c515b..c0cf8f7c5a8e 100644
>>> --- a/fs/btrfs/volumes.c
>>> +++ b/fs/btrfs/volumes.c
>>> @@ -5499,8 +5499,7 @@ static int calc_one_profile_avail(struct btrfs_fs_info *fs_info,
>>>    		goto out;
>>>    	}
>>>    -	devices_info = kcalloc(fs_devices->rw_devices, sizeof(*devices_info),
>>> -			       GFP_NOFS);
>>> +	devices_info = kzalloc_objs(*devices_info, fs_devices->rw_devices, GFP_NOFS);
>>>    	if (!devices_info) {
>>>    		ret = -ENOMEM;
>>>    		goto out;
>>> @@ -6067,8 +6066,7 @@ struct btrfs_block_group *btrfs_create_chunk(struct btrfs_trans_handle *trans,
>>>    	ctl.space_info = space_info;
>>>    	init_alloc_chunk_ctl(fs_devices, &ctl);
>>>    -	devices_info = kcalloc(fs_devices->rw_devices, sizeof(*devices_info),
>>> -			       GFP_NOFS);
>>> +	devices_info = kzalloc_objs(*devices_info, fs_devices->rw_devices, GFP_NOFS);
>>>    	if (!devices_info)
>>>    		return ERR_PTR(-ENOMEM);
>>>    diff --git a/fs/btrfs/zoned.c b/fs/btrfs/zoned.c
>>> index ab330ec957bc..851b0de7bed7 100644
>>> --- a/fs/btrfs/zoned.c
>>> +++ b/fs/btrfs/zoned.c
>>> @@ -1697,8 +1697,7 @@ static int btrfs_load_block_group_raid10(struct btrfs_block_group *bg,
>>>    		return -EINVAL;
>>>    	}
>>>    -	raid0_allocs = kcalloc(map->num_stripes / map->sub_stripes,
>>> sizeof(*raid0_allocs),
>>> -			       GFP_NOFS);
>>> +	raid0_allocs = kzalloc_objs(*raid0_allocs, map->num_stripes / map->sub_stripes, GFP_NOFS);
>>>    	if (!raid0_allocs)
>>>    		return -ENOMEM;
>>>    @@ -1916,7 +1915,7 @@ int btrfs_load_block_group_zone_info(struct
>>> btrfs_block_group *cache, bool new)
>>>      	cache->physical_map = map;
>>>    -	zone_info = kcalloc(map->num_stripes, sizeof(*zone_info), GFP_NOFS);
>>> +	zone_info = kzalloc_objs(*zone_info, map->num_stripes, GFP_NOFS);
>>>    	if (!zone_info) {
>>>    		ret = -ENOMEM;
>>>    		goto out;