The branch main has been updated by markj:
URL:
https://cgit.FreeBSD.org/src/commit/?id=0440b3d2cbf83afb55209a9938b31a48912f222c
commit 0440b3d2cbf83afb55209a9938b31a48912f222c
Author: Mark Johnston <ma...@freebsd.org>
AuthorDate: 2025-05-28 20:45:27 +0000
Commit: Mark Johnston <ma...@freebsd.org>
CommitDate: 2025-05-28 21:05:16 +0000
dtrace: Add compiler barriers around updates to per-CPU flags
Otherwise there's nothing preventing reordering of memory accesses with
respect to these flags being set or cleared. Since their most common
use is to create a section in dtrace probe context where memory faults
are intercepted by dtrace_trap(), such reordering can turn dtrace errors
into fatal exceptions.
MFC after: 2 weeks
Sponsored by: Innovate UK
---
sys/cddl/contrib/opensolaris/uts/common/dtrace/dtrace.c | 2 ++
sys/cddl/contrib/opensolaris/uts/common/sys/dtrace.h | 16 +++++++++++-----
2 files changed, 13 insertions(+), 5 deletions(-)
diff --git a/sys/cddl/contrib/opensolaris/uts/common/dtrace/dtrace.c
b/sys/cddl/contrib/opensolaris/uts/common/dtrace/dtrace.c
index cfd403ac1a01..7192df200ae2 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/dtrace/dtrace.c
+++ b/sys/cddl/contrib/opensolaris/uts/common/dtrace/dtrace.c
@@ -549,10 +549,12 @@ dtrace_load##bits(uintptr_t addr)
\
return (0); \
} \
\
+ __compiler_membar(); \
*flags |= CPU_DTRACE_NOFAULT; \
/*CSTYLED*/ \
rval = *((volatile uint##bits##_t *)addr); \
*flags &= ~CPU_DTRACE_NOFAULT; \
+ __compiler_membar(); \
\
return (!(*flags & CPU_DTRACE_FAULT) ? rval : 0); \
}
diff --git a/sys/cddl/contrib/opensolaris/uts/common/sys/dtrace.h
b/sys/cddl/contrib/opensolaris/uts/common/sys/dtrace.h
index 263b254b9021..c274a9f3357a 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/sys/dtrace.h
+++ b/sys/cddl/contrib/opensolaris/uts/common/sys/dtrace.h
@@ -2421,11 +2421,17 @@ extern void dtrace_helpers_destroy(proc_t *);
#define DTRACE_CPUFLAG_ISSET(flag) \
(cpu_core[curcpu].cpuc_dtrace_flags & (flag))
-#define DTRACE_CPUFLAG_SET(flag) \
- (cpu_core[curcpu].cpuc_dtrace_flags |= (flag))
-
-#define DTRACE_CPUFLAG_CLEAR(flag) \
- (cpu_core[curcpu].cpuc_dtrace_flags &= ~(flag))
+#define DTRACE_CPUFLAG_SET(flag) do { \
+ __compiler_membar(); \
+ cpu_core[curcpu].cpuc_dtrace_flags |= (flag); \
+ __compiler_membar(); \
+} while (0)
+
+#define DTRACE_CPUFLAG_CLEAR(flag) do { \
+ __compiler_membar(); \
+ cpu_core[curcpu].cpuc_dtrace_flags &= ~(flag); \
+ __compiler_membar(); \
+} while (0)
#endif /* _KERNEL */
