linux-kernel - [PATCH AUTOSEL 6.0 21/27] powerpc/rtas: avoid device tree lookups in rtas_os

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Date:   Tue, 27 Dec 2022 15:33:36 -0500
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Nathan Lynch <nathanl@...ux.ibm.com>,
        Nicholas Piggin <npiggin@...il.com>,
        Andrew Donnellan <ajd@...ux.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Sasha Levin <sashal@...nel.org>, ldufour@...ux.ibm.com,
        sourabhjain@...ux.ibm.com, paulus@...abs.org,
        linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH AUTOSEL 6.0 21/27] powerpc/rtas: avoid device tree lookups in rtas_os_term()

From: Nathan Lynch <nathanl@...ux.ibm.com>

[ Upstream commit ed2213bfb192ab51f09f12e9b49b5d482c6493f3 ]

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 an RTAS function token.

Signed-off-by: Nathan Lynch <nathanl@...ux.ibm.com>
Reviewed-by: Nicholas Piggin <npiggin@...il.com>
Reviewed-by: Andrew Donnellan <ajd@...ux.ibm.com>
[mpe: Incorporate suggested change from Nick]
Signed-off-by: Michael Ellerman <mpe@...erman.id.au>
Link: https://lore.kernel.org/r/20221118150751.469393-4-nathanl@linux.ibm.com
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 arch/powerpc/kernel/rtas.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/kernel/rtas.c b/arch/powerpc/kernel/rtas.c
index 0b8a858aa847..082b0c9e0c8a 100644
--- a/arch/powerpc/kernel/rtas.c
+++ b/arch/powerpc/kernel/rtas.c
@@ -875,6 +875,7 @@ 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;
 
 void rtas_os_term(char *str)
 {
@@ -886,14 +887,13 @@ 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)
 		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));
 
@@ -1255,6 +1255,13 @@ 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.
+	 */
+	if (of_property_read_bool(rtas.dev, "ibm,extended-os-term"))
+		ibm_os_term_token = rtas_token("ibm,os-term");
+
 	/* If RTAS was found, allocate the RMO buffer for it and look for
 	 * the stop-self token if any
 	 */
-- 
2.35.1