[PATCH AUTOSEL 4.19 1/4] powerpc/rtas: avoid device tree lookups in rtas_os_term()

Sasha Levin
2022-12-27T20:47:58Z

From: Nathan Lynch <nathanl@linux.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@linux.ibm.com>
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Reviewed-by: Andrew Donnellan <ajd@linux.ibm.com>
[mpe: Incorporate suggested change from Nick]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20221118150751.469393-4-nathanl@linux.ibm.com
Signed-off-by: Sasha Levin <sashal@kernel.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 b492cb1c36fd..4c9ed28465b3 100644
--- a/arch/powerpc/kernel/rtas.c
+++ b/arch/powerpc/kernel/rtas.c
@@ -717,6 +717,7 @@ 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)
{
@@ -728,14 +729,13 @@ 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));

@@ -1332,6 +1332,13 @@ 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