[PATCH 1/3] x86/reboot: Allow "blindly" calling nmi_shootdown_cpus() without a callback

[Sean Christopherson]

Warn if nmi_shootdown_cpus() is called after the crash IPI has been issued
if and only if the caller wants to run a specific callback, and drop the
check nmi_shootdown_cpus_on_restart() whose sole purpose was to avoid
triggering the warning.  This will allow removing the "on restart" variant.

Note, the only caller of nmi_shootdown_cpus_on_restart() unconditionally
disables IRQs, i.e. doubling down on disabling IRQs when a crash IPI has
already been issued doesn't affect the resulting functionality.

Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
 arch/x86/kernel/reboot.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/reboot.c b/arch/x86/kernel/reboot.c
index 615922838c51..25f68952af57 100644
--- a/arch/x86/kernel/reboot.c
+++ b/arch/x86/kernel/reboot.c
@@ -915,10 +915,14 @@ void nmi_shootdown_cpus(nmi_shootdown_cb callback)
 	/*
 	 * Avoid certain doom if a shootdown already occurred; re-registering
 	 * the NMI handler will cause list corruption, modifying the callback
-	 * will do who knows what, etc...
+	 * will do who knows what, etc...  Blindly attempting a shootdown is
+	 * allowed if the caller's goal is purely to ensure a shootdown occurs,
+	 * i.e. if the caller doesn't want to run a specific callback.
 	 */
-	if (WARN_ON_ONCE(crash_ipi_issued))
+	if (crash_ipi_issued) {
+		WARN_ON_ONCE(callback);
 		return;
+	}
 
 	/* Make a note of crashing cpu. Will be used in NMI callback. */
 	crashing_cpu = safe_smp_processor_id();
@@ -956,8 +960,7 @@ void nmi_shootdown_cpus(nmi_shootdown_cb callback)
 
 static inline void nmi_shootdown_cpus_on_restart(void)
 {
-	if (!crash_ipi_issued)
-		nmi_shootdown_cpus(NULL);
+	nmi_shootdown_cpus(NULL);
 }
 
 /*

base-commit: 8cf0b93919e13d1e8d4466eb4080a4c4d9d66d7b
-- 
2.47.0.rc1.288.g06298d1525-goog


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