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From:   SeongJae Park <sj@kernel.org>
To:     stable@vger.kernel.org
Cc:     SeongJae Park <sj@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        damon@lists.linux.dev, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Subject: [PATCH RESEND 6.5.y] mm/damon/sysfs: check DAMOS regions update progress from before_terminate()
Date:   Sat, 28 Oct 2023 21:39:36 +0000
Message-Id: <20231028213936.45621-1-sj@kernel.org>
In-Reply-To: <2023102716-prudishly-reggae-1b29@gregkh>
References: 
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DAMON_SYSFS can receive DAMOS tried regions update request while kdamond
is already out of the main loop and before_terminate callback
(damon_sysfs_before_terminate() in this case) is not yet called.  And
damon_sysfs_handle_cmd() can further be finished before the callback is
invoked.  Then, damon_sysfs_before_terminate() unlocks damon_sysfs_lock,
which is not locked by anyone.  This happens because the callback function
assumes damon_sysfs_cmd_request_callback() should be called before it.
Check if the assumption was true before doing the unlock, to avoid this
problem.

Link: https://lkml.kernel.org/r/20231007200432.3110-1-sj@kernel.org
Fixes: f1d13cacabe1 ("mm/damon/sysfs: implement DAMOS tried regions update command")
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: <stable@vger.kernel.org>	[6.2.x]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
(cherry picked from commit 76b7069bcc89dec33f03eb08abee165d0306b754)
---

I sent this patch yesterday, but seems not archived in lore.kernel.org.
Sending again Cc-ing more mailing lists, to ensure it is sent and others can
find it, to avoid any duplicated works.

 mm/damon/sysfs.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/mm/damon/sysfs.c b/mm/damon/sysfs.c
index 33e1d5c9cb54..df165820c605 100644
--- a/mm/damon/sysfs.c
+++ b/mm/damon/sysfs.c
@@ -1202,6 +1202,8 @@ static int damon_sysfs_set_targets(struct damon_ctx *ctx,
 	return 0;
 }
 
+static bool damon_sysfs_schemes_regions_updating;
+
 static void damon_sysfs_before_terminate(struct damon_ctx *ctx)
 {
 	struct damon_target *t, *next;
@@ -1209,10 +1211,12 @@ static void damon_sysfs_before_terminate(struct damon_ctx *ctx)
 
 	/* damon_sysfs_schemes_update_regions_stop() might not yet called */
 	kdamond = damon_sysfs_cmd_request.kdamond;
-	if (kdamond && damon_sysfs_cmd_request.cmd ==
+	if (kdamond && (damon_sysfs_cmd_request.cmd ==
 			DAMON_SYSFS_CMD_UPDATE_SCHEMES_TRIED_REGIONS &&
+			damon_sysfs_schemes_regions_updating) &&
 			ctx == kdamond->damon_ctx) {
 		damon_sysfs_schemes_update_regions_stop(ctx);
+		damon_sysfs_schemes_regions_updating = false;
 		mutex_unlock(&damon_sysfs_lock);
 	}
 
@@ -1331,7 +1335,6 @@ static int damon_sysfs_commit_input(struct damon_sysfs_kdamond *kdamond)
 static int damon_sysfs_cmd_request_callback(struct damon_ctx *c)
 {
 	struct damon_sysfs_kdamond *kdamond;
-	static bool damon_sysfs_schemes_regions_updating;
 	int err = 0;
 
 	/* avoid deadlock due to concurrent state_store('off') */
-- 
2.34.1