[PATCH] kgdb: disable do_fork and sys_open tests on boot when DEBUG_RODATA is enabled

[Yang Shi]

kgdbts do_fork and sys_open tests are scheduled before mark_rodata_ro gets
called when kgdbts is run on boot. But, the breakpoint is removed by a kernel
thread which may be scheduled after mark_rodata_ro is called. So, this will
cause the below kernel panic:

KGDB: BP remove failed: ffffffc0000c36a8
KGDB: re-enter exception: ALL breakpoints killed
CPU: 0 PID: 2 Comm: kthreadd Not tainted 4.5.0-rc1 #110
Hardware name: Freescale Layerscape 2085a RDB Board (DT)
Call trace:
[<ffffffc00008a998>] dump_backtrace+0x0/0x1b0
[<ffffffc00008ab6c>] show_stack+0x24/0x30
[<ffffffc0004d2644>] dump_stack+0x8c/0xc8
[<ffffffc00017ca08>] kgdb_handle_exception+0x228/0x238
[<ffffffc000096a24>] kgdb_step_brk_fn+0x2c/0x40
[<ffffffc000083c2c>] single_step_handler+0x7c/0x108
[<ffffffc000082474>] do_debug_exception+0x54/0xb8
Exception stack(0xffffffc0797175b0 to 0xffffffc0797176d0)
75a0:                                   ffffffc079714000 ffffffffffffffff
75c0: ffffffc079717770 ffffffc000085418 deadbeefdeadbeef deadbeefdeadbeef
75e0: deadbeefdeadbeef deadbeefdeadbeef deadbeefdeadbeef deadbeefdeadbeef
7600: deadbeefdeadbeef deadbeefdeadbeef deadbeefdeadbeef deadbeefdeadbeef
7620: deadbeefdeadbeef deadbeefdeadbeef deadbeefdeadbeef deadbeefdeadbeef
7640: deadbeefdeadbeef deadbeefdeadbeef ffffffc0000c36a8 000000009600004f
7660: 0000000000000004 00000000d4208000 ffffffc079709580 ffffffc0000c36ac
7680: ffffffc0000c36a8 622f2f2f2f626565 7f7f7f7f7f7f7f7f 63ff332b37603532
76a0: 7f7f7f7f7f7f7f7f 0101010101010101 0000000000000030 0000000000000000
76c0: 0000000000000000 ffffffc001abb11d
[<ffffffc0000854b4>] el1_dbg+0x18/0x6c
[<ffffffc000096dd4>] kgdb_arch_set_breakpoint+0x64/0xe8
[<ffffffc00017bc50>] kgdb_validate_break_address+0x28/0x68
[<ffffffc00017bdd0>] dbg_set_sw_break+0x20/0x118
[<ffffffc00017e440>] gdb_serial_stub+0xc60/0xcc0
[<ffffffc00017c3a8>] kgdb_cpu_enter+0x428/0x6c0
[<ffffffc00017c8e8>] kgdb_handle_exception+0x108/0x238
[<ffffffc000096a24>] kgdb_step_brk_fn+0x2c/0x40
[<ffffffc000083c2c>] single_step_handler+0x7c/0x108
[<ffffffc000082474>] do_debug_exception+0x54/0xb8
Exception stack(0xffffffc079717b50 to 0xffffffc079717c70)
7b40:                                   0000000000000611 ffffffc0000eab88
7b60: ffffffc079717d10 ffffffc000085598 ffffffc079717d10 00000000f2000400
7b80: ffffffc000cbd000 ffffffc000096a38 ffffffc000d84cf3 ffffffc00011a940
7ba0: 0000000500000001 0000000000000000 0000000000000000 0000000000000000
7bc0: 0000000000000000 0000000000000002 ffffffc079717d10 0000000000000000
7be0: ffffffc079717c00 ffffffc000096a60 0000000000800711 ffffffc0000eab88
7c00: ffffffc0763f0e00 0000000000000000 0000000000000000 0000000000000000
7c20: ffffffc079717e60 0000000000000000 0000000000000000 ffffffc000d2d000
7c40: 0000000000001150 010181a300000002 00000000bdb6099c ffffffc0017a96f0
7c60: ed81000001000000 ffffffc07630fb4c
[<ffffffc0000854b4>] el1_dbg+0x18/0x6c
[<ffffffc0000ebac0>] kthreadd+0x1d8/0x268
[<ffffffc000085cd0>] ret_from_fork+0x10/0x40
Kernel panic - not syncing: Recursive entry to debugger

Disable do_fork and sys_open tests on boot, but they still can be run after
the system is bootup.

Signed-off-by: Yang Shi <yang.shi@xxxxxxxxxx>
---
 drivers/misc/kgdbts.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/misc/kgdbts.c b/drivers/misc/kgdbts.c
index 99635dd..4464489 100644
--- a/drivers/misc/kgdbts.c
+++ b/drivers/misc/kgdbts.c
@@ -980,10 +980,12 @@ static void kgdbts_run_tests(void)
 	int i;
 
 	ptr = strchr(config, 'F');
-	if (ptr)
+	if (ptr &&
+	    (!IS_ENABLED(CONFIG_DEBUG_RODATA) || !IS_ENABLED(CONFIG_KGDB_TESTS_ON_BOOT)))
 		fork_test = simple_strtol(ptr + 1, NULL, 10);
 	ptr = strchr(config, 'S');
-	if (ptr)
+	if (ptr &&
+	    (!IS_ENABLED(CONFIG_DEBUG_RODATA) || !IS_ENABLED(CONFIG_KGDB_TESTS_ON_BOOT)))
 		do_sys_open_test = simple_strtol(ptr + 1, NULL, 10);
 	ptr = strchr(config, 'N');
 	if (ptr)
-- 
2.0.2