git: 3fd63ddfdf35 - main - Limit when we call DELAY from KCSAN on amd64

[Andrew Turner]

The branch main has been updated by andrew:

URL: https://cgit.FreeBSD.org/src/commit/?id=3fd63ddfdf3541faea762143365dbc70c16fa49e

commit 3fd63ddfdf3541faea762143365dbc70c16fa49e
Author:     Andrew Turner <andrew at FreeBSD.org>
AuthorDate: 2021-02-05 11:41:17 +0000
Commit:     Andrew Turner <andrew at FreeBSD.org>
CommitDate: 2021-02-25 12:38:05 +0000

    Limit when we call DELAY from KCSAN on amd64
    
    In some cases the DELAY implementation on amd64 can recurse on a spin
    mutex in the i8254 early delay code. Detect when this is going to
    happen and don't call delay in this case. It is safe to not delay here
    with the only issue being KCSAN may not detect data races.
    
    Reviewed by:    kib
    Tested by:      arichardson
    Sponsored by:   Innovate UK
    Differential Revision:  https://reviews.freebsd.org/D28895
---
 sys/amd64/include/csan.h | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/sys/amd64/include/csan.h b/sys/amd64/include/csan.h
index c886daa12f69..9daf8275492c 100644
--- a/sys/amd64/include/csan.h
+++ b/sys/amd64/include/csan.h
@@ -31,6 +31,9 @@
  * $FreeBSD$
  */
 
+#include <sys/timetc.h>
+
+#include <machine/clock.h>
 #include <machine/cpufunc.h>
 #include <machine/stack.h>
 #include <machine/vmparam.h>
@@ -64,7 +67,14 @@ kcsan_md_enable_intrs(uint64_t *state)
 static inline void
 kcsan_md_delay(uint64_t us)
 {
-	DELAY(us);
+	/*
+	 * Only call DELAY if not using the early delay code. The i8254
+	 * early delay function may cause us to recurse on a spin lock
+	 * leading to a panic.
+	 */
+	if ((tsc_is_invariant && tsc_freq != 0) ||
+	    timecounter->tc_quality > 0)
+		DELAY(us);
 }
 
 static void