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>
b0d7f5f0c9