Commit cc879ab3 authored by Benjamin Gray's avatar Benjamin Gray Committed by Michael Ellerman
Browse files

powerpc/watchpoints: Disable preemption in thread_change_pc() 



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 1e60f356 ("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: default avatarBenjamin Gray <bgray@linux.ibm.com>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230829063457.54157-2-bgray@linux.ibm.com
parent 4ff3ba4d

arch/powerpc/kernel/hw_breakpoint.c

+6 −1
Original line number Diff line number Diff line
@@ -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)