Commit ed2213bf authored by Nathan Lynch's avatar Nathan Lynch Committed by Michael Ellerman
Browse files

powerpc/rtas: avoid device tree lookups in rtas_os_term() 



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: default avatarNathan Lynch <nathanl@linux.ibm.com>
Reviewed-by: default avatarNicholas Piggin <npiggin@gmail.com>
Reviewed-by: default avatarAndrew Donnellan <ajd@linux.ibm.com>
[mpe: Incorporate suggested change from Nick]
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20221118150751.469393-4-nathanl@linux.ibm.com
parent b10af504

arch/powerpc/kernel/rtas.c

+10 −3
Original line number Diff line number Diff line
@@ -947,6 +947,7 @@ 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)

{
@@ -958,14 +959,13 @@ 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));
@@ -1335,6 +1335,13 @@ 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

	 */