Re: [PATCH v2] mm/damon/core: fix commit_ops_filters by using correct nth function

[SeongJae Park <sj@kernel.org>]

On Sat,  9 Aug 2025 22:07:56 +0900 Sang-Heon Jeon <ekffu200098@gmail.com> wrote:

> damos_commit_ops_filters() incorrectly uses damos_nth_filter() which
> iterates core_filters. As a result, performing a commit unintentionally
> corrupts ops_filters.
> 
> Add damos_nth_ops_filter() which iterates ops_filters. Use this function
> to fix issues caused by wrong iteration.
> 
> Also, add test to verify that modification is right way.

As I mentioned on v1 thread, please drop the test part, for ease of
backporting.

> 
> Fixes: 3607cc590f18 ("mm/damon/core: support committing ops_filters") # 6.15.x
> Cc: stable@vger.kernel.org
> Signed-off-by: Sang-Heon Jeon <ekffu200098@gmail.com>
> ---
> Changes from v1 [1]:
> 1. Fix code and commit message style.
> 2. Merge patch set into one patch.
> 3. Add fixes and cc section for backporting.
> 
> [1] https://lore.kernel.org/damon/20250808195518.563053-1-ekffu200098@gmail.com/
> 
> ---
> I tried to fix your all comments, but maybe i miss something. Then
> please let me know; I'll fix it as soon as possible.
> 
> ---
>  mm/damon/core.c                               | 14 +++-
>  tools/testing/selftests/damon/Makefile        |  1 +
>  .../damon/sysfs_no_op_commit_break.py         | 72 +++++++++++++++++++
>  3 files changed, 86 insertions(+), 1 deletion(-)
>  create mode 100755 tools/testing/selftests/damon/sysfs_no_op_commit_break.py
> 
> diff --git a/mm/damon/core.c b/mm/damon/core.c
> index 883d791a10e5..19c8f01fc81a 100644
> --- a/mm/damon/core.c
> +++ b/mm/damon/core.c
> @@ -862,6 +862,18 @@ static struct damos_filter *damos_nth_filter(int n, struct damos *s)
>  	return NULL;
>  }
>  
> +static struct damos_filter *damos_nth_ops_filter(int n, struct damos *s)
> +{
> +	struct damos_filter *filter;
> +	int i = 0;
> +
> +	damos_for_each_ops_filter(filter, s) {
> +		if (i++ == n)
> +			return filter;
> +	}
> +	return NULL;
> +}
> +
>  static void damos_commit_filter_arg(
>  		struct damos_filter *dst, struct damos_filter *src)
>  {
> @@ -925,7 +937,7 @@ static int damos_commit_ops_filters(struct damos *dst, struct damos *src)
>  	int i = 0, j = 0;
>  
>  	damos_for_each_ops_filter_safe(dst_filter, next, dst) {
> -		src_filter = damos_nth_filter(i++, src);
> +		src_filter = damos_nth_ops_filter(i++, src);
>  		if (src_filter)
>  			damos_commit_filter(dst_filter, src_filter);
>  		else
> diff --git a/tools/testing/selftests/damon/Makefile b/tools/testing/selftests/damon/Makefile
> index 5b230deb19e8..44a4a819df55 100644
> --- a/tools/testing/selftests/damon/Makefile
> +++ b/tools/testing/selftests/damon/Makefile
> @@ -17,6 +17,7 @@ TEST_PROGS += reclaim.sh lru_sort.sh
>  TEST_PROGS += sysfs_update_removed_scheme_dir.sh
>  TEST_PROGS += sysfs_update_schemes_tried_regions_hang.py
>  TEST_PROGS += sysfs_memcg_path_leak.sh
> +TEST_PROGS += sysfs_no_op_commit_break.py
>  
>  EXTRA_CLEAN = __pycache__
>  
> diff --git a/tools/testing/selftests/damon/sysfs_no_op_commit_break.py b/tools/testing/selftests/damon/sysfs_no_op_commit_break.py
> new file mode 100755
> index 000000000000..fbefb1c83045
> --- /dev/null
> +++ b/tools/testing/selftests/damon/sysfs_no_op_commit_break.py
> @@ -0,0 +1,72 @@
> +#!/usr/bin/env python3
> +# SPDX-License-Identifier: GPL-2.0
> +
> +import json
> +import os
> +import subprocess
> +import sys
> +
> +import _damon_sysfs
> +
> +def dump_damon_status_dict(pid):
> +    try:
> +        subprocess.check_output(['which', 'drgn'], stderr=subprocess.DEVNULL)
> +    except:
> +        return None, 'drgn not found'
> +    file_dir = os.path.dirname(os.path.abspath(__file__))
> +    dump_script = os.path.join(file_dir, 'drgn_dump_damon_status.py')
> +    rc = subprocess.call(['drgn', dump_script, pid, 'damon_dump_output'],
> +        stderr=subprocess.DEVNULL)
> +
> +    if rc != 0:
> +        return None, f'drgn fail: return code({rc})'
> +    try:
> +        with open('damon_dump_output', 'r') as f:
> +            return json.load(f), None
> +    except Exception as e:
> +        return None, 'json.load fail (%s)' % e
> +
> +def main():
> +    kdamonds = _damon_sysfs.Kdamonds(
> +        [_damon_sysfs.Kdamond(
> +            contexts=[_damon_sysfs.DamonCtx(
> +                schemes=[_damon_sysfs.Damos(
> +                    ops_filters=[
> +                        _damon_sysfs.DamosFilter(
> +                            type_='anon',
> +                            matching=True,
> +                            allow=True,
> +                        )
> +                    ]
> +                )],
> +            )])]
> +    )
> +
> +    err = kdamonds.start()
> +    if err is not None:
> +        print('kdamond start failed: %s' % err)
> +        exit(1)
> +
> +    before_commit_status, err = \
> +        dump_damon_status_dict(kdamonds.kdamonds[0].pid)
> +    if err is not None:
> +        print(err)

Adding more context would be nice, e.g.,

    print('before-commit status dump failed: %s' % err)

> +        exit(1)
> +
> +    kdamonds.kdamonds[0].commit()
> +
> +    after_commit_status, err = \
> +        dump_damon_status_dict(kdamonds.kdamonds[0].pid)
> +    if err is not None:
> +        print(err)

Adding more context would be nice, e.g.,

    print('after-commit status dump failed: %s' % err)

> +        exit(1)
> +
> +    if before_commit_status != after_commit_status:
> +        print(f'before: {json.dump(before_commit_status, indent=2)}')
> +        print(f'after: {json.dump(after_commit_status, indent=2)}')
> +        exit(1)
> +
> +    kdamonds.stop()
> +
> +if __name__ == '__main__':
> +    main()
> -- 
> 2.43.0

Other than above two trivial comments, nothing stands out to me.


Thanks,
SJ