[PATCH] riscv: trace: fix snapshot deadlock with sbi ecall
From: Martin Kaiser <hidden>
Date: 2025-12-23 14:07:06
Also in:
linux-riscv, lkml
Subsystem:
risc-v architecture, the rest · Maintainers:
Paul Walmsley, Palmer Dabbelt, Albert Ou, Linus Torvalds
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 <redacted> --- 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 9026400cba10..cabb99cadfb6 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
--
2.43.7