[PATCH 1/1] mm/damon/sysfs: check DAMOS regions update progress from before_terminate()

[PATCH 1/1] mm/damon/sysfs: check DAMOS regions update progress from before_terminate()

[SeongJae Park]

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.

Fixes: f1d13cacabe1 ("mm/damon/sysfs: implement DAMOS tried regions update command")
Cc: <stable@vger.kernel.org> # 6.2.x
Signed-off-by: SeongJae Park <sj@kernel.org>
---
 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 b86ba7b0a921..f60e56150feb 100644
--- a/mm/damon/sysfs.c
+++ b/mm/damon/sysfs.c
@@ -1208,6 +1208,8 @@ 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;
@@ -1219,8 +1221,10 @@ static void damon_sysfs_before_terminate(struct damon_ctx *ctx)
 	cmd = damon_sysfs_cmd_request.cmd;
 	if (kdamond && ctx == kdamond->damon_ctx &&
 			(cmd == DAMON_SYSFS_CMD_UPDATE_SCHEMES_TRIED_REGIONS ||
-			 cmd == DAMON_SYSFS_CMD_UPDATE_SCHEMES_TRIED_BYTES)) {
+			 cmd == DAMON_SYSFS_CMD_UPDATE_SCHEMES_TRIED_BYTES) &&
+			damon_sysfs_schemes_regions_updating) {
 		damon_sysfs_schemes_update_regions_stop(ctx);
+		damon_sysfs_schemes_regions_updating = false;
 		mutex_unlock(&damon_sysfs_lock);
 	}
 
@@ -1340,7 +1344,6 @@ 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;
 	bool total_bytes_only = false;
 	int err = 0;
 
-- 
2.34.1

Re: [PATCH 1/1] mm/damon/sysfs: check DAMOS regions update progress from before_terminate()

[SeongJae Park]

Hello,

On Sat, 7 Oct 2023 20:04:32 +0000 SeongJae Park <sj@kernel.org> wrote:

> 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.
> 
> Fixes: f1d13cacabe1 ("mm/damon/sysfs: implement DAMOS tried regions update command")
> Cc: <stable@vger.kernel.org> # 6.2.x

And this will not cleanly applied to 6.5.y, since this is based on latest
mm-unstable tree.  I will send a backport once this is merged into the
mainline.


Thanks,
SJ

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