@@ -230,13 +230,15 @@ void thread_change_pc(struct task_struct *tsk, struct pt_regs *regs)
struct arch_hw_breakpoint *info;
int i;
+ preempt_disable();
+
for (i = 0; i < nr_wp_slots(); i++) {
struct perf_event *bp = __this_cpu_read(bp_per_reg[i]);
if (unlikely(bp && counter_arch_bp(bp)->perf_single_step))
goto reset;
}
- return;
+ goto out;
reset:
regs_set_return_msr(regs, regs->msr & ~MSR_SE);
@@ -245,6 +247,9 @@ void thread_change_pc(struct task_struct *tsk, struct pt_regs *regs)
__set_breakpoint(i, info);
info->perf_single_step = false;
}
+
+out:
+ preempt_enable();
}
static bool is_larx_stcx_instr(int type)
thread_change_pc() uses CPU local data, so must be protected from swapping CPUs while it is reading the breakpoint struct. The error is more noticeable after 1e60f3564bad ("powerpc/watchpoints: Track perf single step directly on the breakpoint"), which added an unconditional __this_cpu_read() call in thread_change_pc(). However the existing __this_cpu_read() that runs if a breakpoint does need to be re-inserted has the same issue. Signed-off-by: Benjamin Gray <bgray@linux.ibm.com> --- There's probably a more idiomatic way to express this. We technically don't need to disable preemption for the entire function: we should only need to disable preemption within each loop iteration while handling the pointer we are working with. Each iteration itself is independent. --- arch/powerpc/kernel/hw_breakpoint.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)