Re: [PATCH 03/13] powerpc/rtas: avoid device tree lookups in rtas_os_term()
From: "Nicholas Piggin" <npiggin@gmail.com>
Date: 2022-11-28 02:30:30
On Sat Nov 19, 2022 at 1:07 AM AEST, Nathan Lynch wrote:
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.
Nice.
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.
Small nit, but you could do that at the query site unless you were going to start using ibm,os-term without the extended capability. Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
quoted hunk ↗ jump to hunk
Signed-off-by: Nathan Lynch <redacted> --- 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