Re: [RFC PATCH 02/10] mm/damon/sysfs: add pause file under context dir

[SeongJae Park <sj@kernel.org>]

On Sun, 15 Mar 2026 14:00:01 -0700 SeongJae Park <sj@kernel.org> wrote:

> Add pause DAMON sysfs file under the context directory.  It exposes the
> damon_ctx->pause API parameter to the users so that they can use the
> pause/resume feature.
> 
> Signed-off-by: SeongJae Park <sj@kernel.org>
> ---
>  mm/damon/sysfs.c | 30 ++++++++++++++++++++++++++++++
>  1 file changed, 30 insertions(+)
> 
> diff --git a/mm/damon/sysfs.c b/mm/damon/sysfs.c
> index 576d1ddd736bf..4cbb8b9aaba3c 100644
> --- a/mm/damon/sysfs.c
> +++ b/mm/damon/sysfs.c
> @@ -866,6 +866,7 @@ struct damon_sysfs_context {
>  	struct damon_sysfs_attrs *attrs;
>  	struct damon_sysfs_targets *targets;
>  	struct damon_sysfs_schemes *schemes;
> +	bool pause;
>  };

sashiko.dev comments [1] below.

: Is the new pause field left uninitialized when a context is allocated?
: 
: Looking at damon_sysfs_context_alloc(), memory is allocated via kmalloc_obj()
: which does not zero-fill by default, and the new field is not explicitly
: initialized:
: 
: static struct damon_sysfs_context *damon_sysfs_context_alloc(
:                 enum damon_ops_id ops_id)
: {
:         struct damon_sysfs_context *context = kmalloc_obj(*context);
: 
:         if (!context)
:                 return NULL;
:         context->kobj = (struct kobject){};
:         context->ops_id = ops_id;
:         context->addr_unit = 1;
:         return context;
: }
: 
: If a user reads the pause sysfs file before writing to it, could this return
: uninitialized kernel heap memory?

Good catch.  I will add below fixup to the next spin.

'''
--- a/mm/damon/sysfs.c
+++ b/mm/damon/sysfs.c
@@ -1432,6 +1432,7 @@ static struct damon_sysfs_context *damon_sysfs_context_alloc(
        context->kobj = (struct kobject){};
        context->ops_id = ops_id;
        context->addr_unit = 1;
+       context->pause = false;
        return context;
 }
'''

Btw, somehow sashiko.dev added the comment to not this patch but the sixth
patch of this series.

[1] https://sashiko.dev/#/patchset/20260315210012.94846-7-sj@kernel.org


Thanks,
SJ

[...]