6.17-stable review patch. If anyone has any objections, please let me know.
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From: Quanmin Yan yanquanmin1@huawei.com
commit 9fd7bb5083d1e1027b8ac1e365c29921ab88b177 upstream.
In DAMON's damon_sysfs_repeat_call_fn(), time_before() is used to compare the current jiffies with next_update_jiffies to determine whether to update the sysfs files at this moment.
On 32-bit systems, the kernel initializes jiffies to "-5 minutes" to make jiffies wrap bugs appear earlier. However, this causes time_before() in damon_sysfs_repeat_call_fn() to unexpectedly return true during the first 5 minutes after boot on 32-bit systems (see [1] for more explanation, which fixes another jiffies-related issue before). As a result, DAMON does not update sysfs files during that period.
There is also an issue unrelated to the system's word size[2]: if the user stops DAMON just after next_update_jiffies is updated and restarts it after 'refresh_ms' or a longer delay, next_update_jiffies will retain an older value, causing time_before() to return false and the update to happen earlier than expected.
Fix these issues by making next_update_jiffies a global variable and initializing it each time DAMON is started.
Link: https://lkml.kernel.org/r/20251030020746.967174-3-yanquanmin1@huawei.com Link: https://lkml.kernel.org/r/20250822025057.1740854-1-ekffu200098@gmail.com [1] Link: https://lore.kernel.org/all/20251029013038.66625-1-sj@kernel.org/ [2] Fixes: d809a7c64ba8 ("mm/damon/sysfs: implement refresh_ms file internal work") Suggested-by: SeongJae Park sj@kernel.org Reviewed-by: SeongJae Park sj@kernel.org Signed-off-by: Quanmin Yan yanquanmin1@huawei.com Cc: Kefeng Wang wangkefeng.wang@huawei.com Cc: ze zuo zuoze1@huawei.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- mm/damon/sysfs.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-)
--- a/mm/damon/sysfs.c +++ b/mm/damon/sysfs.c @@ -1514,16 +1514,17 @@ static struct damon_ctx *damon_sysfs_bui return ctx; }
+static unsigned long damon_sysfs_next_update_jiffies; + static int damon_sysfs_repeat_call_fn(void *data) { struct damon_sysfs_kdamond *sysfs_kdamond = data; - static unsigned long next_update_jiffies;
if (!sysfs_kdamond->refresh_ms) return 0; - if (time_before(jiffies, next_update_jiffies)) + if (time_before(jiffies, damon_sysfs_next_update_jiffies)) return 0; - next_update_jiffies = jiffies + + damon_sysfs_next_update_jiffies = jiffies + msecs_to_jiffies(sysfs_kdamond->refresh_ms);
if (!mutex_trylock(&damon_sysfs_lock)) @@ -1569,6 +1570,9 @@ static int damon_sysfs_turn_damon_on(str } kdamond->damon_ctx = ctx;
+ damon_sysfs_next_update_jiffies = + jiffies + msecs_to_jiffies(kdamond->refresh_ms); + repeat_call_control->fn = damon_sysfs_repeat_call_fn; repeat_call_control->data = kdamond; repeat_call_control->repeat = true;