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ring-buffer: Have rb_time_cmpxchg() set the msb counter too

PATCH New Steven Rostedt 1 participant 1 message Dec 15, 2023

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Steven Rostedt

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PATCH 1/1 ring-buffer: Have rb_time_cmpxchg() set the msb counter too

From: "Steven Rostedt (Google)" <[email protected]>

The rb_time_cmpxchg() on 32-bit architectures requires setting three 32-bit words to represent the 64-bit timestamp, with some salt for synchronization. Those are: msb, top, and bottom

The issue is, the rb_time_cmpxchg() did not properly salt the msb portion, and the msb that was written was stale.

Fixes f03f2abce4f39 ("ring-buffer: Have 32 bit time stamps use all 64 bits")
Signed-off-by Steven Rostedt (Google) <[email protected]>
---
 kernel/trace/ring_buffer.c | 2 ++
 1 file changed, 2 insertions(+)
kernel/trace/ring_buffer.c +2 -0
index 78aacc78f03a..e9c10eabdb95 100644
@@ -722,10 +722,12 @@ static bool rb_time_cmpxchg(rb_time_t *t, u64 expect, u64 set)
 	 cnt2 = cnt + 1;
 
 	 rb_time_split(val, &top, &bottom, &msb);
+	 msb = rb_time_val_cnt(msb, cnt);
 	 top = rb_time_val_cnt(top, cnt);
 	 bottom = rb_time_val_cnt(bottom, cnt);
 
 	 rb_time_split(set, &top2, &bottom2, &msb2);
+	 msb2 = rb_time_val_cnt(msb2, cnt);
 	 top2 = rb_time_val_cnt(top2, cnt2);
 	 bottom2 = rb_time_val_cnt(bottom2, cnt2);
Signature · 1 line
2.42.0