Re: [PATCH v2] mm/damon/tests/sysfs-kunit: fix leaked pid reference in add_targets test

[SJ Park <sj@kernel.org>]

Hello Xiaolei,

On Thu, 29 Oct 2026 15:56:09 +0800 Xiaolei Wang <xiaoleiwangxiaolei@gmail.com> wrote:

> From: Wang Xiaolei <xiaoleiwangxiaolei@gmail.com>
> 
> damon_sysfs_test_add_targets() creates its monitoring context with
> damon_new_ctx(), which leaves ctx->ops zero-initialized.  Since
> DAMON_OPS_VADDR is zero, damon_target_has_pid() returns true for the
> context, and damon_sysfs_add_targets() therefore calls
> damon_set_target_pid() for each target it adds.  That function grabs a
> reference to the target's struct pid via find_get_pid().
> 
> The test then tears the context down with damon_destroy_ctx(), which
> releases such a reference from ctx->ops.cleanup_target().  For the vaddr
> operations set that callback is damon_va_cleanup_target(), and it is the
> only place where the reference is put.  The test never selects an
> operations set, though, so cleanup_target is NULL and both references --
> one for each of the two damon_sysfs_add_targets() calls -- are leaked on
> every run of the test.  Running the test with CONFIG_DEBUG_KMEMLEAK
> enabled reports the leaked struct pid objects as unreferenced.
> 
> Fix this by selecting the vaddr operations set for the context before
> adding the targets, mirroring what the sysfs interface does.
> damon_select_ops() fails if the vaddr operations set is not registered,
> in which case the test cannot exercise the pid handling and skips
> itself.

Makes sense.  Thank you for finding and fixing this.

> 
> Fixes: b8ee5575f763 ("mm/damon/sysfs-test: add a unit test for damon_sysfs_set_targets()")

The impact is leak.  I think we should add Cc: stable@.

Cc: <stable@vger.kernel.org> # 6.7.x

> Cc: Liam R. Howlett <liam@infradead.org>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Mike Rapoport <rppt@kernel.org>
> Cc: Suren Baghdasaryan <surenb@google.com>
> Cc: Vlastimil Babka <vbabka@kernel.org>
> Signed-off-by: Wang Xiaolei <xiaoleiwangxiaolei@gmail.com>

Other than Cc: stable@,

Reviewed-by: SJ Park <sj@kernel.org>

Assuming you agree to Cc stable@, I applied this patch to damon/next [1] tree
after adding the Cc.  I will repost it next Monday, as an mm.git merge request.
So, no action from your side is needed for now.

[1] https://origin.kernel.org/doc/html/latest/mm/damon/maintainer-profile.html#scm-trees


Thanks,
SJ

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