The following commit has been merged into the timers/core branch of tip:
Commit-ID: 8c111f1b967687f47bb0cfbedf2863b62c23223c
Gitweb: https://git.kernel.org/tip/8c111f1b967687f47bb0cfbedf2863b62c23223c
Author: Jeff Layton <jlayton@xxxxxxxxxx>
AuthorDate: Tue, 10 Sep 2024 13:43:34 -04:00
Committer: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitterDate: Wed, 02 Oct 2024 18:06:03 +02:00
timekeeping: Don't use seqcount loop in ktime_mono_to_any() on 64-bit systems
ktime_mono_to_any() only fetches the offset inside the loop. This is a
single word on 64-bit CPUs, and seqcount_read_begin() implies a full SMP
barrier.
Use READ_ONCE() to fetch the offset instead of doing a seqcount loop on
64-bit and add the matching WRITE_ONCE()'s to update the offsets in
tk_set_wall_to_mono() and tk_update_sleep_time().
[ tglx: Get rid of the #ifdeffery ]
Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/all/20240910-mgtime-v3-1-84406ed53fad@xxxxxxxxxx
---
kernel/time/timekeeping.c | 16 +++++++++++++---
1 file changed, 13 insertions(+), 3 deletions(-)
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 47e44b9..a57f2ee 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -161,13 +161,15 @@ static void tk_set_wall_to_mono(struct timekeeper *tk, struct timespec64 wtm)
WARN_ON_ONCE(tk->offs_real != timespec64_to_ktime(tmp));
tk->wall_to_monotonic = wtm;
set_normalized_timespec64(&tmp, -wtm.tv_sec, -wtm.tv_nsec);
- tk->offs_real = timespec64_to_ktime(tmp);
- tk->offs_tai = ktime_add(tk->offs_real, ktime_set(tk->tai_offset, 0));
+ /* Paired with READ_ONCE() in ktime_mono_to_any() */
+ WRITE_ONCE(tk->offs_real, timespec64_to_ktime(tmp));
+ WRITE_ONCE(tk->offs_tai, ktime_add(tk->offs_real, ktime_set(tk->tai_offset, 0)));
}
static inline void tk_update_sleep_time(struct timekeeper *tk, ktime_t delta)
{
- tk->offs_boot = ktime_add(tk->offs_boot, delta);
+ /* Paired with READ_ONCE() in ktime_mono_to_any() */
+ WRITE_ONCE(tk->offs_boot, ktime_add(tk->offs_boot, delta));
/*
* Timespec representation for VDSO update to avoid 64bit division
* on every update.
@@ -930,6 +932,14 @@ ktime_t ktime_mono_to_any(ktime_t tmono, enum tk_offsets offs)
unsigned int seq;
ktime_t tconv;
+ if (IS_ENABLED(CONFIG_64BIT)) {
+ /*
+ * Paired with WRITE_ONCE()s in tk_set_wall_to_mono() and
+ * tk_update_sleep_time().
+ */
+ return ktime_add(tmono, READ_ONCE(*offset));
+ }
+
do {
seq = read_seqcount_begin(&tk_core.seq);
tconv = ktime_add(tmono, *offset);
|