linux-kernel - [PATCH v2] powerpc/xmon: Also setup debugger hooks when single-stepping

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Message-Id: <20180523180054.9937-1-msuchanek@suse.de>
Date:   Wed, 23 May 2018 20:00:54 +0200
From:   Michal Suchanek <msuchanek@...e.de>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Balbir Singh <bsingharora@...il.com>,
        Nicholas Piggin <npiggin@...il.com>,
        Breno Leitao <leitao@...ian.org>,
        Vaibhav Jain <vaibhav@...ux.vnet.ibm.com>,
        "Guilherme G. Piccoli" <gpiccoli@...ux.vnet.ibm.com>,
        Michal Suchanek <msuchanek@...e.de>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: [PATCH v2] powerpc/xmon: Also setup debugger hooks when single-stepping

When single-stepping kernel code from xmon without a debug hook enabled
the kernel crashes. This can happen when kernel starts with xmon on
crash disabled but xmon is entered using sysrq.

Call force_enable_xmon when single-stepping in xmon to install the xmon
debug hooks.

Fixes: e1368d0c9edb ("powerpc/xmon: Setup debugger hooks when first
break-point is set")

Signed-off-by: Michal Suchanek <msuchanek@...e.de>
---
 arch/powerpc/xmon/xmon.c | 21 +++++++++++----------
 1 file changed, 11 insertions(+), 10 deletions(-)

v2: calling force_enable_xmon in do_step is sufficient

diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
index a0842f1ff72c..252df9741d20 100644
--- a/arch/powerpc/xmon/xmon.c
+++ b/arch/powerpc/xmon/xmon.c
@@ -778,6 +778,16 @@ static int xmon_fault_handler(struct pt_regs *regs)
 	return 0;
 }
 
+/* Force enable xmon if not already enabled */
+static inline void force_enable_xmon(void)
+{
+	/* Enable xmon hooks if needed */
+	if (!xmon_on) {
+		printf("xmon: Enabling debugger hooks\n");
+		xmon_on = 1;
+	}
+}
+
 static struct bpt *at_breakpoint(unsigned long pc)
 {
 	int i;
@@ -1094,6 +1104,7 @@ static int do_step(struct pt_regs *regs)
 	unsigned int instr;
 	int stepped;
 
+	force_enable_xmon();
 	/* check we are in 64-bit kernel mode, translation enabled */
 	if ((regs->msr & (MSR_64BIT|MSR_PR|MSR_IR)) == (MSR_64BIT|MSR_IR)) {
 		if (mread(regs->nip, &instr, 4) == 4) {
@@ -1268,16 +1279,6 @@ static long check_bp_loc(unsigned long addr)
 	return 1;
 }
 
-/* Force enable xmon if not already enabled */
-static inline void force_enable_xmon(void)
-{
-	/* Enable xmon hooks if needed */
-	if (!xmon_on) {
-		printf("xmon: Enabling debugger hooks\n");
-		xmon_on = 1;
-	}
-}
-
 static char *breakpoint_help_string =
     "Breakpoint command usage:\n"
     "b                show breakpoints\n"
-- 
2.13.6