+ samples-damon-prcl-handle-damon_start-failure.patch added to mm-new branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: samples/damon/prcl: handle damon_start() failure
has been added to the -mm mm-new branch.  Its filename is
     samples-damon-prcl-handle-damon_start-failure.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/samples-damon-prcl-handle-damon_start-failure.patch

This patch will later appear in the mm-new branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews.  Please do not hesitate to respond to
review feedback and post updated versions to replace or incrementally
fixup patches in mm-new.

The mm-new branch of mm.git is not included in linux-next

If a few days of testing in mm-new is successful, the patch will me moved
into mm.git's mm-unstable branch, which is included in linux-next

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------------------------------------------------------
From: SJ Park <sj@kernel.org>
Subject: samples/damon/prcl: handle damon_start() failure
Date: Sun, 28 Jun 2026 14:54:41 -0700

damon_sample_prcl_start() callers assume it will clean up resources when
it fails.  And the function does the cleanup for context buildup failures.
However, it is not doing the cleanup for damon_start() failure.  As a
result, when damon_start() fails, it leaks the memory for DAMON context. 
Free the context in case of the failure to fix the issues.

Note that the issue can reliably be reproduced because the module calls
damon_start() in the exclusive mode.  For example,

    $ sudo damo start
    $ echo $$ | sudo tee /sys/module/damon_sample_prcl/parameters/target_pid
    $ echo Y | sudo tee /sys/module/damon_sample_prcl/parameters/enabled
    $ sudo cat /proc/allocinfo | grep damon_new_ctx

Because the first command is running another DAMON instance, the third
command fails the damon_start() call because the new DAMON instance cannot
exclusively run.  And without this fix, by repeating the third and the
fourth commands above, we can show the memory consumption is only
increasing due to the leaks.  It requires the sudo permission though.

The issue was discovered [1] by Sashiko.

Link: https://lore.kernel.org/20260628215447.96166-3-sj@kernel.org
Link: https://lore.kernel.org/20260609145814.70163-1-sj@kernel.org [1]
Fixes: 2aca254620a8 ("samples/damon: introduce a skeleton of a smaple DAMON module for proactive reclamation")
Signed-off-by: SJ Park <sj@kernel.org>
Reviewed-by: Zenghui Yu <zenghui.yu@linux.dev>
Cc: <stable@vger.kernel.org> # 6.14.x
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 samples/damon/prcl.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/samples/damon/prcl.c~samples-damon-prcl-handle-damon_start-failure
+++ a/samples/damon/prcl.c
@@ -106,8 +106,10 @@ static int damon_sample_prcl_start(void)
 	damon_set_schemes(ctx, &scheme, 1);
 
 	err = damon_start(&ctx, 1, true);
-	if (err)
+	if (err) {
+		damon_destroy_ctx(ctx);
 		return err;
+	}
 
 	repeat_call_control.data = ctx;
 	return damon_call(ctx, &repeat_call_control);
_

Patches currently in -mm which might be from sj@kernel.org are

mm-damon-sysfs-schemes-fix-dir-put-orders-in-access_pattern_add_dirs.patch
mm-damon-sysfs-schemes-put-stats-for-scheme_add_dirs-internal-error.patch
mm-damon-ops-common-handle-extreme-intervals-in-damon_hot_score.patch
maintainers-s-seongjae-sj.patch
samples-damon-wsse-handle-damon_start-failure.patch
samples-damon-prcl-handle-damon_start-failure.patch
samples-damon-mtier-handle-damon_start-failure.patch
samples-damon-mtier-handle-damon_stop-failure.patch
samples-damon-wsse-stop-and-free-damon-ctx-when-damon_call-fails.patch
samples-damon-prcl-stop-and-free-damon-ctx-when-damon_call-fails.patch