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 2f6ce7e714ef842e43120ecd6a7ed287b502026d upstream.
Patch series "mm/damon: fixes for the jiffies-related issues", v2.
On 32-bit systems, the kernel initializes jiffies to "-5 minutes" to make jiffies wrap bugs appear earlier. However, this may cause the time_before() series of functions to return unexpected values, resulting in DAMON not functioning as intended. Meanwhile, similar issues exist in some specific user operation scenarios.
This patchset addresses these issues. The first patch is about the DAMON_STAT module, and the second patch is about the core layer's sysfs.
This patch (of 2):
In DAMON_STAT's damon_stat_damon_call_fn(), time_before_eq() is used to avoid unnecessarily frequent stat update.
On 32-bit systems, the kernel initializes jiffies to "-5 minutes" to make jiffies wrap bugs appear earlier. However, this causes time_before_eq() in DAMON_STAT 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_STAT does not update any monitoring results during that period, which becomes more confusing when DAMON_STAT_ENABLED_DEFAULT is enabled.
There is also an issue unrelated to the system's word size[2]: if the user stops DAMON_STAT just after last_refresh_jiffies is updated and restarts it after 5 seconds or a longer delay, last_refresh_jiffies will retain an older value, causing time_before_eq() to return false and the update to happen earlier than expected.
Fix these issues by making last_refresh_jiffies a global variable and initializing it each time DAMON_STAT is started.
Link: https://lkml.kernel.org/r/20251030020746.967174-2-yanquanmin1@huawei.com Link: https://lkml.kernel.org/r/20250822025057.1740854-1-ekffu200098@gmail.com [1] Link: https://lore.kernel.org/all/20251028143250.50144-1-sj@kernel.org/ [2] Fixes: fabdd1e911da ("mm/damon/stat: calculate and expose estimated memory bandwidth") Signed-off-by: Quanmin Yan yanquanmin1@huawei.com Suggested-by: SeongJae Park sj@kernel.org Reviewed-by: SeongJae Park sj@kernel.org 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/stat.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-)
--- a/mm/damon/stat.c +++ b/mm/damon/stat.c @@ -41,6 +41,8 @@ MODULE_PARM_DESC(memory_idle_ms_percenti
static struct damon_ctx *damon_stat_context;
+static unsigned long damon_stat_last_refresh_jiffies; + static void damon_stat_set_estimated_memory_bandwidth(struct damon_ctx *c) { struct damon_target *t; @@ -125,13 +127,12 @@ static void damon_stat_set_idletime_perc static int damon_stat_damon_call_fn(void *data) { struct damon_ctx *c = data; - static unsigned long last_refresh_jiffies;
/* avoid unnecessarily frequent stat update */ - if (time_before_eq(jiffies, last_refresh_jiffies + + if (time_before_eq(jiffies, damon_stat_last_refresh_jiffies + msecs_to_jiffies(5 * MSEC_PER_SEC))) return 0; - last_refresh_jiffies = jiffies; + damon_stat_last_refresh_jiffies = jiffies;
damon_stat_set_estimated_memory_bandwidth(c); damon_stat_set_idletime_percentiles(c); @@ -204,6 +205,8 @@ static int damon_stat_start(void) err = damon_start(&damon_stat_context, 1, true); if (err) return err; + + damon_stat_last_refresh_jiffies = jiffies; call_control.data = damon_stat_context; return damon_call(damon_stat_context, &call_control); }