mm/damon/core: use time_in_range_open() for damos quota window start

damos_adjust_quota() uses time_after_eq() to show if it is time to start a
new quota charge window, comparing the current jiffies and the scheduled
next charge window start time.  If it is, the next charge window start
time is updated and the new charge window starts.

The time check and next window start time update is skipped while the
scheme is deactivated by the watermarks.  Let's suppose the deactivation
is kept more than LONG_MAX jiffies (assuming CONFIG_HZ of 250, more than
99 days in 32 bit systems and more than one billion years in 64 bit
systems), resulting in having the jiffies larger than the next charge
window start time + LONG_MAX.  Then, the time_after_eq() call can return
false until another LONG_MAX jiffies are passed.

This means the scheme can continue working after being reactivated by the
watermarks.  But, soon, the quota will be exceeded and the scheme will
again effectively stop working until the next charge window starts.
Because the current charge window is extended to up to LONG_MAX jiffies,
however, it will look like it stopped unexpectedly and indefinitely, from
the user's perspective.

Fix this by using !time_in_range_open() instead.

The issue was discovered [1] by sashiko.

Link: https://lore.kernel.org/20260329152306.45796-1-sj@kernel.org
Link: https://lore.kernel.org/20260324040722.57944-1-sj@kernel.org
Fixes: ee801b7dd782 ("mm/damon/schemes: activate schemes based on a watermarks mechanism")
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: <stable@vger.kernel.org> # 5.16.x
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/damon/core.c b/mm/damon/core.c
index 19642c175568905720f0e6cf8bbf6f3e0381dd05..3bc7a2bbfe7def505b3089a2dd0d545b00494bb1 100644 (file)
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -2449,7 +2449,8 @@ static void damos_adjust_quota(struct damon_ctx *c, struct damos *s)
        }
 
        /* New charge window starts */
-       if (time_after_eq(jiffies, quota->charged_from +
+       if (!time_in_range_open(jiffies, quota->charged_from,
+                               quota->charged_from +
                                msecs_to_jiffies(quota->reset_interval))) {
                if (damos_quota_is_set(quota) &&
                                quota->charged_sz >= quota->esz)