Subject: [PATCH 03/13] powerpc/rtas: avoid device tree lookups in rtas_os_term()

From: Nathan Lynch <[email-masked]>
Date: Fri, 18 Nov 2022 09:07:41 -0600

rtas_os_term() is called during panic. Its behavior depends on a
couple of conditions in the /rtas node of the device tree, the
traversal of which entails locking and local IRQ state changes. If the
kernel panics while devtree_lock is held, rtas_os_term() as currently
written could hang.

Instead of discovering the relevant characteristics at panic time,
cache them in file-static variables at boot. Note the lookup for
"ibm,extended-os-term" is converted to of_property_read_bool() since
it is a boolean property, not a RTAS function token.

Signed-off-by: Nathan Lynch <[email-masked]>
---
 arch/powerpc/kernel/rtas.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/kernel/rtas.c b/arch/powerpc/kernel/rtas.c
index c12dd5ed5e00..81e4996012b7 100644
--- a/arch/powerpc/kernel/rtas.c
+++ b/arch/powerpc/kernel/rtas.c
@@ -947,6 +947,8 @@ void __noreturn rtas_halt(void)
 
 /* Must be in the RMO region, so we place it here */
 static char rtas_os_term_buf[2048];
+static s32 ibm_os_term_token = RTAS_UNKNOWN_SERVICE;
+static bool ibm_extended_os_term;
 
 void rtas_os_term(char *str)
 {
@@ -958,14 +960,13 @@ void rtas_os_term(char *str)
 	 * this property may terminate the partition which we want to avoid
 	 * since it interferes with panic_timeout.
 	 */
-	if (RTAS_UNKNOWN_SERVICE == rtas_token("ibm,os-term") ||
-	    RTAS_UNKNOWN_SERVICE == rtas_token("ibm,extended-os-term"))
+	if (ibm_os_term_token == RTAS_UNKNOWN_SERVICE || !ibm_extended_os_term)
 		return;
 
 	snprintf(rtas_os_term_buf, 2048, "OS panic: %s", str);
 
 	do {
-		status = rtas_call(rtas_token("ibm,os-term"), 1, 1, NULL,
+		status = rtas_call(ibm_os_term_token, 1, 1, NULL,
 				   __pa(rtas_os_term_buf));
 	} while (rtas_busy_delay(status));
 
@@ -1335,6 +1336,13 @@ void __init rtas_initialize(void)
 	no_entry = of_property_read_u32(rtas.dev, "linux,rtas-entry", &entry);
 	rtas.entry = no_entry ? rtas.base : entry;
 
+	/*
+	 * Discover these now to avoid device tree lookups in the
+	 * panic path.
+	 */
+	ibm_os_term_token = rtas_token("ibm,os-term");
+	ibm_extended_os_term = of_property_read_bool(rtas.dev, "ibm,extended-os-term");
+
 	/* If RTAS was found, allocate the RMO buffer for it and look for
 	 * the stop-self token if any
 	 */
-- 
2.37.1