On Sat, 30 Dec 2023 16:51:56 -0500
Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
> Below is the patch for 6.1 of this change, and it depends on:
>
> 20231230164736.3b8c86c4@xxxxxxxxxxxxxxxxxx
And this is for 5.15.
-- Steve
---
kernel/trace/ring_buffer.c | 77 ++++++++++++++-------------------------------
1 file changed, 24 insertions(+), 53 deletions(-)
Index: test-linux.git/kernel/trace/ring_buffer.c
===================================================================
--- test-linux.git.orig/kernel/trace/ring_buffer.c 2023-12-30 16:51:29.022248800 -0500
+++ test-linux.git/kernel/trace/ring_buffer.c 2023-12-30 16:51:47.278447539 -0500
@@ -691,44 +691,6 @@ rb_time_read_cmpxchg(local_t *l, unsigne
return ret == expect;
}
-static int rb_time_cmpxchg(rb_time_t *t, u64 expect, u64 set)
-{
- unsigned long cnt, top, bottom;
- unsigned long cnt2, top2, bottom2;
- u64 val;
-
- /* Any interruptions in this function should cause a failure */
- cnt = local_read(&t->cnt);
-
- /* The cmpxchg always fails if it interrupted an update */
- if (!__rb_time_read(t, &val, &cnt2))
- return false;
-
- if (val != expect)
- return false;
-
- if ((cnt & 3) != cnt2)
- return false;
-
- cnt2 = cnt + 1;
-
- rb_time_split(val, &top, &bottom);
- top = rb_time_val_cnt(top, cnt);
- bottom = rb_time_val_cnt(bottom, cnt);
-
- rb_time_split(set, &top2, &bottom2);
- top2 = rb_time_val_cnt(top2, cnt2);
- bottom2 = rb_time_val_cnt(bottom2, cnt2);
-
- if (!rb_time_read_cmpxchg(&t->cnt, cnt, cnt2))
- return false;
- if (!rb_time_read_cmpxchg(&t->top, top, top2))
- return false;
- if (!rb_time_read_cmpxchg(&t->bottom, bottom, bottom2))
- return false;
- return true;
-}
-
#else /* 64 bits */
/* local64_t always succeeds */
@@ -742,13 +704,6 @@ static void rb_time_set(rb_time_t *t, u6
{
local64_set(&t->time, val);
}
-
-static bool rb_time_cmpxchg(rb_time_t *t, u64 expect, u64 set)
-{
- u64 val;
- val = local64_cmpxchg(&t->time, expect, set);
- return val == expect;
-}
#endif
/*
@@ -3562,20 +3517,36 @@ __rb_reserve_next(struct ring_buffer_per
} else {
u64 ts;
/* SLOW PATH - Interrupted between A and C */
- a_ok = rb_time_read(&cpu_buffer->write_stamp, &info->after);
- /* Was interrupted before here, write_stamp must be valid */
+
+ /* Save the old before_stamp */
+ a_ok = rb_time_read(&cpu_buffer->before_stamp, &info->before);
RB_WARN_ON(cpu_buffer, !a_ok);
+
+ /*
+ * Read a new timestamp and update the before_stamp to make
+ * the next event after this one force using an absolute
+ * timestamp. This is in case an interrupt were to come in
+ * between E and F.
+ */
ts = rb_time_stamp(cpu_buffer->buffer);
+ rb_time_set(&cpu_buffer->before_stamp, ts);
+
+ barrier();
+ /*E*/ a_ok = rb_time_read(&cpu_buffer->write_stamp, &info->after);
+ /* Was interrupted before here, write_stamp must be valid */
+ RB_WARN_ON(cpu_buffer, !a_ok);
barrier();
- /*E*/ if (write == (local_read(&tail_page->write) & RB_WRITE_MASK) &&
- info->after < ts &&
- rb_time_cmpxchg(&cpu_buffer->write_stamp,
- info->after, ts)) {
- /* Nothing came after this event between C and E */
+ /*F*/ if (write == (local_read(&tail_page->write) & RB_WRITE_MASK) &&
+ info->after == info->before && info->after < ts) {
+ /*
+ * Nothing came after this event between C and F, it is
+ * safe to use info->after for the delta as it
+ * matched info->before and is still valid.
+ */
info->delta = ts - info->after;
} else {
/*
- * Interrupted between C and E:
+ * Interrupted between C and F:
* Lost the previous events time stamp. Just set the
* delta to zero, and this will be the same time as
* the event this event interrupted. And the events that
