From mboxrd@z Thu Jan 1 00:00:00 1970 From: panand@redhat.com (Pratyush Anand) Date: Fri, 26 May 2017 16:42:33 +0530 Subject: Query: arm64: hwbreakpoint: single stepping in case of custom overflow_handler Message-ID: To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org Hi Will, When we run test from samples/hw_breakpoint/data_breakpoint.c, it triggers continuous watchpoint exception handler. Reproducer: # insmod data_breakpoint.ko ksym=__sysrq_enabled # cat /proc/sys/kernel/sysrq So, wanted to understand that why do we not allow single stepping in case overflow_handler is a customized one and not from perf infrastructure? Patch [1] allows to work with a custom overflow_handler, but I am not sure if that could be an acceptable choice. There are issues with samples/hw_breakpoint/data_breakpoint.c, even when using patch [1],because overflow_handler of test calls dump_stack(). I am not yet sure,what happened here..my guess is that dump_stack() triggered a SW BRK exception somewhere. Anyway,thats a secondary problem,I can look into if patch [1] makes sense. ~Pratyush [1] diff --git a/arch/arm64/kernel/hw_breakpoint.c b/arch/arm64/kernel/hw_breakpoint.c index 749f81779420..ea8ab0656dd0 100644 --- a/arch/arm64/kernel/hw_breakpoint.c +++ b/arch/arm64/kernel/hw_breakpoint.c @@ -661,7 +661,7 @@ static int breakpoint_handler(unsigned long unused, unsigned int esr, perf_bp_event(bp, regs); /* Do we need to handle the stepping? */ - if (is_default_overflow_handler(bp)) + if (bp->overflow_handler) step = 1; unlock: rcu_read_unlock(); @@ -789,7 +789,7 @@ static int watchpoint_handler(unsigned long addr, unsigned int esr, perf_bp_event(wp, regs); /* Do we need to handle the stepping? */ - if (is_default_overflow_handler(wp)) + if (wp->overflow_handler) step = 1; } if (min_dist > 0 && min_dist != -1) { @@ -800,7 +800,7 @@ static int watchpoint_handler(unsigned long addr, unsigned int esr, perf_bp_event(wp, regs); /* Do we need to handle the stepping? */ - if (is_default_overflow_handler(wp)) + if (wp->overflow_handler) step = 1; } rcu_read_unlock();