x86,kgdb: Add low level debug hook

The only way the debugger can handle a trap in inside rcu_lock,
notify_die, or atomic_notifier_call_chain without a triple fault is
to have a low level "first opportunity handler" in the int3 exception
handler.

Generally this will be something the vast majority of folks will not
need, but for those who need it, it is added as a kernel .config
option called KGDB_LOW_LEVEL_TRAP.

CC: Ingo Molnar <mingo@elte.hu>
CC: Thomas Gleixner <tglx@linutronix.de>
CC: H. Peter Anvin <hpa@zytor.com>
CC: x86@kernel.org
Signed-off-by: Jason Wessel <jason.wessel@windriver.com>

diff --git a/arch/x86/include/asm/kgdb.h b/arch/x86/include/asm/kgdb.h
index e6c6c808489fc1bb5d9d6bf9920484749fb041db..006da3687cdcccfc44adff4726edbef9230088d9 100644 (file)
--- a/arch/x86/include/asm/kgdb.h
+++ b/arch/x86/include/asm/kgdb.h
@@ -76,4 +76,7 @@ static inline void arch_kgdb_breakpoint(void)
 #define BREAK_INSTR_SIZE       1
 #define CACHE_FLUSH_IS_SAFE    1
 
+extern int kgdb_ll_trap(int cmd, const char *str,
+                       struct pt_regs *regs, long err, int trap, int sig);
+
 #endif /* _ASM_X86_KGDB_H */

diff --git a/arch/x86/kernel/kgdb.c b/arch/x86/kernel/kgdb.c
index acba57169938e5f786d30b0a4d7f44ec3e134e20..95b89d4cb8f18f1595a430e0e6eaf8ac5f513487 100644 (file)
--- a/arch/x86/kernel/kgdb.c
+++ b/arch/x86/kernel/kgdb.c
@@ -538,7 +538,7 @@ static int __kgdb_notify(struct die_args *args, unsigned long cmd)
                        return NOTIFY_DONE;
        }
 
-       if (kgdb_handle_exception(args->trapnr, args->signr, args->err, regs))
+       if (kgdb_handle_exception(args->trapnr, args->signr, cmd, regs))
                return NOTIFY_DONE;
 
        /* Must touch watchdog before return to normal operation */
@@ -546,6 +546,26 @@ static int __kgdb_notify(struct die_args *args, unsigned long cmd)
        return NOTIFY_STOP;
 }
 
+#ifdef CONFIG_KGDB_LOW_LEVEL_TRAP
+int kgdb_ll_trap(int cmd, const char *str,
+                struct pt_regs *regs, long err, int trap, int sig)
+{
+       struct die_args args = {
+               .regs   = regs,
+               .str    = str,
+               .err    = err,
+               .trapnr = trap,
+               .signr  = sig,
+
+       };
+
+       if (!kgdb_io_module_registered)
+               return NOTIFY_DONE;
+
+       return __kgdb_notify(&args, cmd);
+}
+#endif /* CONFIG_KGDB_LOW_LEVEL_TRAP */
+
 static int
 kgdb_notify(struct notifier_block *self, unsigned long cmd, void *ptr)
 {

diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 02cfb9b8f5b10f8d282715cc7a79fd49e04b7468..7eaad4c5110a15934bc24b162acb274a85bf82c7 100644 (file)
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -15,6 +15,7 @@
 #include <linux/kprobes.h>
 #include <linux/uaccess.h>
 #include <linux/kdebug.h>
+#include <linux/kgdb.h>
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/ptrace.h>
@@ -451,6 +452,11 @@ void restart_nmi(void)
 /* May run on IST stack. */
 dotraplinkage void __kprobes do_int3(struct pt_regs *regs, long error_code)
 {
+#ifdef CONFIG_KGDB_LOW_LEVEL_TRAP
+       if (kgdb_ll_trap(DIE_INT3, "int3", regs, error_code, 3, SIGTRAP)
+                       == NOTIFY_STOP)
+               return;
+#endif /* CONFIG_KGDB_LOW_LEVEL_TRAP */
 #ifdef CONFIG_KPROBES
        if (notify_die(DIE_INT3, "int3", regs, error_code, 3, SIGTRAP)
                        == NOTIFY_STOP)

diff --git a/include/linux/kgdb.h b/include/linux/kgdb.h
index 406f6f9286f3f9d6fd7f6fc236721914e1110fd2..19d1b29a26947bd81c8302d334f0fe349f19febf 100644 (file)
--- a/include/linux/kgdb.h
+++ b/include/linux/kgdb.h
@@ -60,6 +60,7 @@ struct uart_port;
 void kgdb_breakpoint(void);
 
 extern int kgdb_connected;
+extern int kgdb_io_module_registered;
 
 extern atomic_t                        kgdb_setting_breakpoint;
 extern atomic_t                        kgdb_cpu_doing_single_step;

diff --git a/kernel/debug/debug_core.c b/kernel/debug/debug_core.c
index 88a83a225374a7bfebe5973785b405faa67bb4f6..375e42f0baf0fc305b1f650bd092297750c85852 100644 (file)
--- a/kernel/debug/debug_core.c
+++ b/kernel/debug/debug_core.c
@@ -66,7 +66,7 @@ int                           kgdb_connected;
 EXPORT_SYMBOL_GPL(kgdb_connected);
 
 /* All the KGDB handlers are installed */
-static int                     kgdb_io_module_registered;
+int                    kgdb_io_module_registered;
 
 /* Guard for recursive entry */
 static int                     exception_level;

diff --git a/lib/Kconfig.kgdb b/lib/Kconfig.kgdb
index ee8ae7132f209abe86ff5c8422c02dac940c7607..c56ccb4ad292dee7c0554bf41cf3b06767754717 100644 (file)
--- a/lib/Kconfig.kgdb
+++ b/lib/Kconfig.kgdb
@@ -57,6 +57,15 @@ config KGDB_TESTS_BOOT_STRING
          information about other strings you could use beyond the
          default of V1F100.
 
+config KGDB_LOW_LEVEL_TRAP
+       bool "KGDB: Allow debugging with traps in notifiers"
+       depends on X86
+       default n
+       help
+         This will add an extra call back to kgdb for the breakpoint
+         exception handler on which will will allow kgdb to step
+         through a notify handler.
+
 config KGDB_KDB
        bool "KGDB_KDB: include kdb frontend for kgdb"
        default n