[PATCH 6.18 081/175] riscv: trace: fix snapshot deadlock with sbi ecall

Greg Kroah-Hartman
2026-02-09T14:29:38Z

From: Martin Kaiser <martin@kaiser.cx>

[ Upstream commit b0d7f5f0c9f05f1b6d4ee7110f15bef9c11f9df0 ]

If sbi_ecall.c's functions are traceable,

echo "__sbi_ecall:snapshot" > /sys/kernel/tracing/set_ftrace_filter

may get the kernel into a deadlock.

(Functions in sbi_ecall.c are excluded from tracing if
CONFIG_RISCV_ALTERNATIVE_EARLY is set.)

__sbi_ecall triggers a snapshot of the ringbuffer. The snapshot code
raises an IPI interrupt, which results in another call to __sbi_ecall
and another snapshot...

All it takes to get into this endless loop is one initial __sbi_ecall.
On RISC-V systems without SSTC extension, the clock events in
timer-riscv.c issue periodic sbi ecalls, making the problem easy to
trigger.

Always exclude the sbi_ecall.c functions from tracing to fix the
potential deadlock.

sbi ecalls can easiliy be logged via trace events, excluding ecall
functions from function tracing is not a big limitation.

Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Link: https://patch.msgid.link/20251223135043.1336524-1-martin@kaiser.cx
Signed-off-by: Paul Walmsley <pjw@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/riscv/kernel/Makefile | 15 ++++++++-------
1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
index f60fce69b7259..a01f6439d62b1 100644
--- a/arch/riscv/kernel/Makefile
+++ b/arch/riscv/kernel/Makefile
@@ -3,12 +3,6 @@
# Makefile for the RISC-V Linux kernel
#

-ifdef CONFIG_FTRACE
-CFLAGS_REMOVE_ftrace.o = $(CC_FLAGS_FTRACE)
-CFLAGS_REMOVE_patch.o = $(CC_FLAGS_FTRACE)
-CFLAGS_REMOVE_sbi.o = $(CC_FLAGS_FTRACE)
-CFLAGS_REMOVE_return_address.o = $(CC_FLAGS_FTRACE)
-endif
CFLAGS_syscall_table.o += $(call cc-disable-warning, override-init)
CFLAGS_compat_syscall_table.o += $(call cc-disable-warning, override-init)

@@ -24,7 +18,6 @@ CFLAGS_sbi_ecall.o := -mcmodel=medany
ifdef CONFIG_FTRACE
CFLAGS_REMOVE_alternative.o = $(CC_FLAGS_FTRACE)
CFLAGS_REMOVE_cpufeature.o = $(CC_FLAGS_FTRACE)
-CFLAGS_REMOVE_sbi_ecall.o = $(CC_FLAGS_FTRACE)
endif
ifdef CONFIG_RELOCATABLE
CFLAGS_alternative.o += -fno-pie
@@ -43,6 +36,14 @@ CFLAGS_sbi_ecall.o += -D__NO_FORTIFY
endif
endif

+ifdef CONFIG_FTRACE
+CFLAGS_REMOVE_ftrace.o = $(CC_FLAGS_FTRACE)
+CFLAGS_REMOVE_patch.o = $(CC_FLAGS_FTRACE)
+CFLAGS_REMOVE_sbi.o = $(CC_FLAGS_FTRACE)
+CFLAGS_REMOVE_return_address.o = $(CC_FLAGS_FTRACE)
+CFLAGS_REMOVE_sbi_ecall.o = $(CC_FLAGS_FTRACE)
+endif
+
always-$(KBUILD_BUILTIN) += vmlinux.lds

obj-y += head.o
--
2.51.0