From 880c43b185ca52239e75bc546cc4f4d9154d0fed Mon Sep 17 00:00:00 2001 From: FUJITA Tomonori Date: Tue, 14 Jul 2026 07:52:35 +0900 Subject: [PATCH] rust: time: fix as_micros_ceil() to round correctly for negative Delta The ceiling-division idiom `(n + d - 1) / d` only produces the correct result when `n` is non-negative. For example, if n = -1000 (exactly -1us), the old code computed (-1000 + 999) / 1000 == 0 instead of -1. For negative n, truncating division already rounds towards positive infinity, so no bias is needed in that case. Fixes: fae0cdc12340 ("rust: time: Introduce Delta type") Signed-off-by: FUJITA Tomonori Acked-by: Andreas Hindborg Cc: stable@vger.kernel.org Link: https://patch.msgid.link/20260713225235.3243480-1-tomo@flapping.org Signed-off-by: Miguel Ojeda --- rust/kernel/time.rs | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff --git a/rust/kernel/time.rs b/rust/kernel/time.rs index 363e93cbb139..b8463823aed9 100644 --- a/rust/kernel/time.rs +++ b/rust/kernel/time.rs @@ -441,15 +441,22 @@ pub const fn as_nanos(self) -> i64 { /// to the value in the [`Delta`]. #[inline] pub fn as_micros_ceil(self) -> i64 { + let n = self.as_nanos(); + let n = if n >= 0 { + n.saturating_add(NSEC_PER_USEC - 1) + } else { + n + }; + #[cfg(CONFIG_64BIT)] { - self.as_nanos().saturating_add(NSEC_PER_USEC - 1) / NSEC_PER_USEC + n / NSEC_PER_USEC } #[cfg(not(CONFIG_64BIT))] // SAFETY: It is always safe to call `ktime_to_us()` with any value. unsafe { - bindings::ktime_to_us(self.as_nanos().saturating_add(NSEC_PER_USEC - 1)) + bindings::ktime_to_us(n) } }