The patch titled Subject: mm/damon/core: set quota->charged_from to jiffies at first charge window has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-damon-core-set-quota-charged_from-to-jiffies-at-first-charge-window.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: Sang-Heon Jeon ekffu200098@gmail.com Subject: mm/damon/core: set quota->charged_from to jiffies at first charge window Date: Fri, 22 Aug 2025 11:50:57 +0900

Kernel initializes the "jiffies" timer as 5 minutes below zero, as shown in include/linux/jiffies.h

/* * Have the 32 bit jiffies value wrap 5 minutes after boot * so jiffies wrap bugs show up earlier. */ #define INITIAL_JIFFIES ((unsigned long)(unsigned int) (-300*HZ))

And jiffies comparison help functions cast unsigned value to signed to cover wraparound

#define time_after_eq(a,b) \ (typecheck(unsigned long, a) && \ typecheck(unsigned long, b) && \ ((long)((a) - (b)) >= 0))

When quota->charged_from is initialized to 0, time_after_eq() can incorrectly return FALSE even after reset_interval has elapsed. This occurs when (jiffies - reset_interval) produces a value with MSB=1, which is interpreted as negative in signed arithmetic.

This issue primarily affects 32-bit systems because: On 64-bit systems: MSB=1 values occur after ~292 million years from boot (assuming HZ=1000), almost impossible.

On 32-bit systems: MSB=1 values occur during the first 5 minutes after boot, and the second half of every jiffies wraparound cycle, starting from day 25 (assuming HZ=1000)

When above unexpected FALSE return from time_after_eq() occurs, the charging window will not reset. The user impact depends on esz value at that time.

If esz is 0, scheme ignores configured quotas and runs without any limits.

If esz is not 0, scheme stops working once the quota is exhausted. It remains until the charging window finally resets.

So, change quota->charged_from to jiffies at damos_adjust_quota() when it is considered as the first charge window. By this change, we can avoid unexpected FALSE return from time_after_eq()

Link: https://lkml.kernel.org/r/20250822025057.1740854-1-ekffu200098@gmail.com Fixes: 2b8a248d5873 ("mm/damon/schemes: implement size quota for schemes application speed control") # 5.16 Signed-off-by: Sang-Heon Jeon ekffu200098@gmail.com Reviewed-by: SeongJae Park sj@kernel.org Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/damon/core.c | 4 ++++ 1 file changed, 4 insertions(+)

--- a/mm/damon/core.c~mm-damon-core-set-quota-charged_from-to-jiffies-at-first-charge-window +++ a/mm/damon/core.c @@ -2111,6 +2111,10 @@ static void damos_adjust_quota(struct da if (!quota->ms && !quota->sz && list_empty(&quota->goals)) return;

+ /* First charge window */ + if (!quota->total_charged_sz && !quota->charged_from) + quota->charged_from = jiffies; + /* New charge window starts */ if (time_after_eq(jiffies, quota->charged_from + msecs_to_jiffies(quota->reset_interval))) { _

Patches currently in -mm which might be from ekffu200098@gmail.com are

mm-damon-core-set-quota-charged_from-to-jiffies-at-first-charge-window.patch mm-damon-update-expired-description-of-damos_action.patch docs-mm-damon-design-fix-typo-s-sz_trtied-sz_tried.patch selftests-damon-test-no-op-commit-broke-damon-status.patch selftests-damon-test-no-op-commit-broke-damon-status-fix.patch mm-damon-tests-core-kunit-add-damos_commit_filter-test.patch