ARM: hw_breakpoint: do not allocate new breakpoints with preemption disabled

The watchpoint single-stepping code calls register_user_hw_breakpoint to
register a mismatch breakpoint for stepping over the watchpoint. This is
performed with preemption disabled, which is unsafe as we may end up scheduling
whilst in_atomic(). Furthermore, using the perf API is rather overkill since
we are already in the hw-breakpoint backend and only require access to reserved
breakpoints anyway.

This patch reworks the watchpoint stepping code so that we don't require
another perf_event for the mismatch breakpoint. Instead, we hold a separate
arch_hw_breakpoint_ctrl struct inside the watchpoint which is used exclusively
for stepping. We can check whether or not stepping is enabled when installing
or uninstalling the watchpoint and operate on the breakpoint accordingly.

Signed-off-by: Will Deacon <will.deacon@arm.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/arch/arm/include/asm/hw_breakpoint.h b/arch/arm/include/asm/hw_breakpoint.h
index 4d8ae9d67abe..881429d0b849 100644
--- a/arch/arm/include/asm/hw_breakpoint.h
+++ b/arch/arm/include/asm/hw_breakpoint.h
@@ -20,7 +20,7 @@ struct arch_hw_breakpoint_ctrl {
 struct arch_hw_breakpoint {
         u32     address;
         u32     trigger;
-        struct perf_event *suspended_wp;
+        struct arch_hw_breakpoint_ctrl step_ctrl;
         struct arch_hw_breakpoint_ctrl ctrl;
 };