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

["Miquel Sabaté Solà" <mssola@mssola.com>]

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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.

>
> 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;

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