From: Nathan Lynch <nath...@linux.ibm.com>
Enabling any of the powerpc:rtas_* tracepoints at boot is likely to
result in an oops on RTAS platforms. For example, booting a QEMU
pseries model with 'trace_event=powerpc:rtas_input' in the command
line leads to:
BUG: Kernel NULL pointer dereference on read at 0x00000008
Oops: Kernel access of bad area, sig: 7 [#1]
NIP [c00000000004231c] do_enter_rtas+0x1bc/0x460
LR [c00000000004231c] do_enter_rtas+0x1bc/0x460
Call Trace:
do_enter_rtas+0x1bc/0x460 (unreliable)
rtas_call+0x22c/0x4a0
rtas_get_boot_time+0x80/0x14c
read_persistent_clock64+0x124/0x150
read_persistent_wall_and_boot_offset+0x28/0x58
timekeeping_init+0x70/0x348
start_kernel+0xa0c/0xc1c
start_here_common+0x1c/0x20
(This is preceded by a warning for the failed lookup in
rtas_token_to_function().)
This happens when __do_enter_rtas_trace() attempts a token to function
descriptor lookup before the xarray containing the mappings has been
set up.
Fall back to linear scan of the table if rtas_token_to_function_xarray
is empty.
Fixes: 24098f580e2b ("powerpc/rtas: add tracepoints around RTAS entry")
Reviewed-by: Aneesh Kumar K.V (IBM) <aneesh.ku...@kernel.org>
Signed-off-by: Nathan Lynch <nath...@linux.ibm.com>
---
arch/powerpc/kernel/rtas.c | 18 ++++++++++++++----
1 file changed, 14 insertions(+), 4 deletions(-)
diff --git a/arch/powerpc/kernel/rtas.c b/arch/powerpc/kernel/rtas.c
index ae9b10c954a1..f60a8e7bd5ed 100644
--- a/arch/powerpc/kernel/rtas.c
+++ b/arch/powerpc/kernel/rtas.c
@@ -572,11 +572,21 @@ static const struct rtas_function
*rtas_token_to_function(s32 token)
return NULL;
func = rtas_token_to_function_untrusted(token);
+ if (func)
+ return func;
+ /*
+ * Fall back to linear scan in case the reverse mapping hasn't
+ * been initialized yet.
+ */
+ if (xa_empty(&rtas_token_to_function_xarray)) {
+ for_each_rtas_function(func) {
+ if (func->token == token)
+ return func;
+ }
+ }
- if (WARN_ONCE(!func, "unexpected failed lookup for token %d", token))
- return NULL;
-
- return func;
+ WARN_ONCE(true, "unexpected failed lookup for token %d", token);
+ return NULL;
}
/* This is here deliberately so it's only used in this file */
--
2.41.0
