linux-kernel - [PATCH] powerpc/xmon: really enable xmon when a breakpoint is set

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Date:   Mon, 21 May 2018 15:21:08 +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>,
        "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
        Vaibhav Jain <vaibhav@...ux.vnet.ibm.com>,
        "Guilherme G. Piccoli" <gpiccoli@...ux.vnet.ibm.com>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Cc:     Michal Suchanek <msuchanek@...e.de>
Subject: [PATCH] powerpc/xmon: really enable xmon when a breakpoint is set

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.

Commit e1368d0c9edb ("powerpc/xmon: Setup debugger hooks when first
break-point is set") adds force_enable_xmon function that prints
"xmon: Enabling debugger hooks" but does not enable them.

Add the call to xmon_init to install the debugger hooks in
force_enable_xmon and also call force_enable_xmon when single-stepping
in xmon.

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 | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
index a0842f1ff72c..504bd1c3d8b0 100644
--- a/arch/powerpc/xmon/xmon.c
+++ b/arch/powerpc/xmon/xmon.c
@@ -179,6 +179,9 @@ static const char *getvecname(unsigned long vec);
 
 static int do_spu_cmd(void);
 
+static void xmon_init(int enable);
+static inline void force_enable_xmon(void);
+
 #ifdef CONFIG_44x
 static void dump_tlb_44x(void);
 #endif
@@ -1094,6 +1097,7 @@ 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) {
@@ -1275,6 +1279,7 @@ static inline void force_enable_xmon(void)
 	if (!xmon_on) {
 		printf("xmon: Enabling debugger hooks\n");
 		xmon_on = 1;
+		xmon_init(1);
 	}
 }
 
-- 
2.13.6