Hi Tiezhu,
On Tue, Sep 8, 2026 at 3:58 PM Tiezhu Yang <yangtiezhu@loongson.cn> wrote:
>
> v2: Use single variable "need_sigtrap" to send SIGTRAP in do_watch().
>
> This series addresses severe functional degradations in standard
> perf_event usage, including initialization failures and one-shot
> triggering limitations.
>
> All fixes have been verified with user-space reproducers on real
> hardware and align with the LoongArch Reference Manual.
>
> Here is a user-space reproducer demonstrating that standard perf
> hardware breakpoints can now reliably monitor 10,000 hits without
> a single event leakage or subsystem lockup.
>
> (1) Test program (perf-hw-breakpoint.c):
>
> #include <stdint.h>
> #include <stdio.h>
> #include <sys/ioctl.h>
> #include <sys/syscall.h>
> #include <unistd.h>
> #include <linux/hw_breakpoint.h>
> #include <linux/perf_event.h>
>
> #ifndef noinline
> #define noinline __attribute__((noinline))
> #endif
>
> static noinline void test_function(const uint8_t *data)
> {
> asm volatile("" :: "r"(data[0]) : "memory");
> }
>
> int main(void)
> {
> int fd, ret, i;
> size_t count;
> uint8_t data[] = "TEST DATA";
> struct perf_event_attr attr = {0};
>
> attr.type = PERF_TYPE_BREAKPOINT;
> attr.size = sizeof(struct perf_event_attr);
> attr.bp_type = HW_BREAKPOINT_RW;
> attr.bp_addr = (uintptr_t)data;
> attr.bp_len = HW_BREAKPOINT_LEN_1;
> attr.exclude_kernel = 1;
> attr.exclude_hv = 1;
> attr.disabled = 1;
>
> fd = syscall(__NR_perf_event_open, &attr, 0, -1, -1, 0);
> ioctl(fd, PERF_EVENT_IOC_RESET, 0);
> ioctl(fd, PERF_EVENT_IOC_ENABLE, 0);
>
> for (i = 0; i < 10000; i++)
> test_function(data);
>
> ioctl(fd, PERF_EVENT_IOC_DISABLE, 0);
> read(fd, &count, sizeof(size_t));
>
> printf("perf count = %zu\n", count);
>
> close(fd);
> return 0;
> }
>
> (2) Test steps:
>
> $ gcc perf-hw-breakpoint.c -o perf-hw-breakpoint
> $ ./perf-hw-breakpoint
>
> (3) Test results:
>
> Without this series:
>
> perf count = 0
>
> With this series:
>
> perf count = 10000
>
> Tiezhu Yang (6):
> LoongArch: Fix bitmask corruption in update_bp_registers()
> LoongArch: Remove redundant call in update_bp_registers()
> LoongArch: Fix architectural naming typo for CSR_FWPS_SKIP
> LoongArch: Only send SIGTRAP signal if necessary in do_watch()
> LoongArch: Fix perf hardware breakpoint failure via installation
> LoongArch: Fix one-shot limitation for perf hardware breakpoints
Thanks! Without these patches, perf-event tests always fail; with
them, they fail intermittently.
Reproduce with:
1. git clone https://github.com/jimblandy/perf-event && cd perf-event
2. cargo test -r # or --test breakpoint
Best,
Rui
>
> arch/loongarch/include/asm/hw_breakpoint.h | 4 +-
> arch/loongarch/include/asm/loongarch.h | 7 +++-
> arch/loongarch/kernel/hw_breakpoint.c | 43 ++++++++++++++++------
> arch/loongarch/kernel/traps.c | 12 +++---
> 4 files changed, 46 insertions(+), 20 deletions(-)
>
> --
> 2.42.0
>
>