git: eaed922eda58 - main - panic()/KERNEL_PANICKED(): Move back to using 'panicstr' as a flag

The branch main has been updated by olce:

URL: https://cgit.FreeBSD.org/src/commit/?id=eaed922eda584da7306e7c371ff6adf3fc4dc4c3

commit eaed922eda584da7306e7c371ff6adf3fc4dc4c3
Author:     Olivier Certner <olce@FreeBSD.org>
AuthorDate: 2024-01-18 10:15:18 +0000
Commit:     Olivier Certner <olce@FreeBSD.org>
CommitDate: 2024-01-26 21:07:56 +0000

    panic()/KERNEL_PANICKED(): Move back to using 'panicstr' as a flag
    
    Currently, no performance-critical path tests for a panic.  Moreover, we
    today have KERNEL_PANICKED() which wraps the test into
    __predict_false(), already catering to those (potential) use cases.
    Also, in practice we don't support 64-bit architectures without caches,
    so reading an 'int' instead of a pointer doesn't (directly) save any
    memory access.  Finally, 'panicked' is redundant with 'panicstr' (and
    wastes a tiny amount of memory).
    
    Consequently:
    1. Use again 'panicstr' as a flag indicating that the system is
    panicking.  To this end:
      - Modify panic() so that it ensures this pointer is set to some
        non-NULL value even if the caller didn't pass any panic string.
      - Modify KERNEL_PANICKED() to test for 'panicstr'.
      - Remove 'panicked'.
    2. Annotate 'panicstr' with '__read_mostly' (instead of using
    '__read_frequently' as for 'panicked').  This may have to be changed if,
    in the future, some performance-intensive path needs to test it.
    3. Convert a few more direct tests of 'panicstr' to using
    KERNEL_PANICKED().
    
    Reviewed by:            kib, markj, emaste
    Approved by:            markj (mentor)
    MFC after:              2 weeks
    Sponsored by:           The FreeBSD Foundation
    Differential Revision:  https://reviews.freebsd.org/D43569
---
 sys/kern/kern_shutdown.c | 15 +++++++++++----
 sys/sys/kassert.h        |  3 +--
 2 files changed, 12 insertions(+), 6 deletions(-)

diff --git a/sys/kern/kern_shutdown.c b/sys/kern/kern_shutdown.c
index 3b0e3997c852..d66c7ba0d344 100644
--- a/sys/kern/kern_shutdown.c
+++ b/sys/kern/kern_shutdown.c
@@ -224,8 +224,7 @@ SYSCTL_INT(_kern, OID_AUTO, kerneldump_gzlevel, CTLFLAG_RWTUN,
  * Variable panicstr contains argument to first call to panic; used as flag
  * to indicate that the kernel has already called panic.
  */
-const char *panicstr;
-bool __read_frequently panicked;
+const char *panicstr __read_mostly;
 
 int __read_mostly dumping;		/* system is dumping */
 int rebooting;				/* system is rebooting */
@@ -899,6 +898,15 @@ vpanic(const char *fmt, va_list ap)
 	int bootopt, newpanic;
 	static char buf[256];
 
+	/*
+	 * 'fmt' must not be NULL as it is put into 'panicstr' which is then
+	 * used as a flag to detect if the kernel has panicked.  Also, although
+	 * vsnprintf() supports a NULL 'fmt' argument, use a more informative
+	 * message.
+	 */
+	if (fmt == NULL)
+		fmt = "<no panic string!>";
+
 	spinlock_enter();
 
 #ifdef SMP
@@ -907,7 +915,7 @@ vpanic(const char *fmt, va_list ap)
 	 * concurrently entering panic.  Only the winner will proceed
 	 * further.
 	 */
-	if (panicstr == NULL && !kdb_active) {
+	if (!KERNEL_PANICKED() && !kdb_active) {
 		other_cpus = all_cpus;
 		CPU_CLR(PCPU_GET(cpuid), &other_cpus);
 		stop_cpus_hard(other_cpus);
@@ -927,7 +935,6 @@ vpanic(const char *fmt, va_list ap)
 	else {
 		bootopt |= RB_DUMP;
 		panicstr = fmt;
-		panicked = true;
 		newpanic = 1;
 	}
 
diff --git a/sys/sys/kassert.h b/sys/sys/kassert.h
index 7b54ac6ae519..da8701ce3858 100644
--- a/sys/sys/kassert.h
+++ b/sys/sys/kassert.h
@@ -35,8 +35,7 @@
 
 #ifdef _KERNEL
 extern const char *panicstr;	/* panic message */
-extern bool panicked;
-#define	KERNEL_PANICKED()	__predict_false(panicked)
+#define	KERNEL_PANICKED()	__predict_false(panicstr != NULL)
 
 /*
  * Trap accesses going through a pointer. Moreover if kasan is available trap