If there are no objections, I will commit the following patch.
--
This patch fixes some corner cases where KGDB will silently hang or
kill the system, if a user accidentally tries to source step into a
spin_unlock() call or source step in on a macro containing
smp_processor_id(). The use of raw_smp_processor_id is desired in
kernel/kgdb.c to fix this particular problem.
To fix issues with accidental source step in on spin_unlock(), the
idea is to check for the existence of a break point on the second
entry to kgdb and try to remove it. Next an attempt will be made to
continue normal operations. A third entry will generate a panic(), so
as to stop infinite loops.
Testing has shown that kgdb is much more robust with these changes
and "random accidental run control".
Signed-off-by: Jason Wessel <[EMAIL PROTECTED]>
---
arch/i386/kernel/kgdb.c | 8 ++++++++
kernel/kgdb.c | 47
++++++++++++++++++++++++++++++++++++++++-------
2 files changed, 48 insertions(+), 7 deletions(-)
Index: linux-2.6.21.1/kernel/kgdb.c
===================================================================
--- linux-2.6.21.1.orig/kernel/kgdb.c
+++ linux-2.6.21.1/kernel/kgdb.c
@@ -70,6 +70,8 @@ int kgdb_connected;
int kgdb_may_fault;
/* All the KGDB handlers are installed */
int kgdb_from_module_registered = 0;
+/* Guard for recursive entry */
+static int exception_level = 0;
/* We provide a kgdb_io_ops structure that may be overriden. */
struct kgdb_io __attribute__ ((weak)) kgdb_io_ops;
@@ -166,6 +168,12 @@ int __attribute__ ((weak))
return 0;
}
+unsigned long __attribute__ ((weak))
+ kgdb_arch_pc(int exception, struct pt_regs *regs)
+{
+ return instruction_pointer(regs);
+}
+
static int hex(char ch)
{
if ((ch >= 'a') && (ch <= 'f'))
@@ -580,11 +588,11 @@ static void kgdb_wait(struct pt_regs *re
int processor;
local_irq_save(flags);
- processor = smp_processor_id();
+ processor = raw_smp_processor_id();
kgdb_info[processor].debuggerinfo = regs;
kgdb_info[processor].task = current;
atomic_set(&procindebug[processor], 1);
- atomic_set(&kgdb_sync_softlockup[smp_processor_id()], 1);
+ atomic_set(&kgdb_sync_softlockup[raw_smp_processor_id()], 1);
/* Wait till master processor goes completely into the debugger.
* FIXME: this looks racy */
@@ -784,7 +792,7 @@ static inline int shadow_pid(int realpid
if (realpid) {
return realpid;
}
- return pid_max + smp_processor_id();
+ return pid_max + raw_smp_processor_id();
}
static char gdbmsgbuf[BUFMAX + 1];
@@ -848,12 +856,36 @@ int kgdb_handle_exception(int ex_vector,
long kgdb_usethreadid = 0;
int error = 0, all_cpus_synced = 0;
struct pt_regs *shadowregs;
- int processor = smp_processor_id();
+ int processor = raw_smp_processor_id();
void *local_debuggerinfo;
/* Panic on recursive debugger calls. */
- if (atomic_read(&debugger_active) == smp_processor_id() + 1)
+ if (atomic_read(&debugger_active) == raw_smp_processor_id() + 1) {
+ exception_level++;
+ addr = kgdb_arch_pc(ex_vector, linux_regs);
+ kgdb_deactivate_sw_breakpoints();
+ if (kgdb_remove_sw_break(addr) == 0) {
+ /* If the break point removed ok at the place exception
+ * occurred, try to recover and print a warning to the end
+ * user because the user planted a breakpoint in a place
+ * that KGDB needs in order to function.
+ */
+ exception_level = 0;
+ kgdb_skipexception(ex_vector, linux_regs);
+ kgdb_activate_sw_breakpoints();
+ printk(KERN_CRIT "KGDB: re-enter exception: breakpoint
removed\n");
+ WARN_ON(1);
+ return 0;
+ }
+ remove_all_break();
+ kgdb_skipexception(ex_vector, linux_regs);
+ if (exception_level > 1)
+ panic("Recursive entry to debugger");
+
+ printk(KERN_CRIT "KGDB: re-enter exception: ALL breakpoints
removed\n");
+ panic("Recursive entry to debugger");
return 0;
+ }
acquirelock:
@@ -864,7 +896,7 @@ int kgdb_handle_exception(int ex_vector,
local_irq_save(flags);
/* Hold debugger_active */
- procid = smp_processor_id();
+ procid = raw_smp_processor_id();
while (cmpxchg(&atomic_read(&debugger_active), 0, (procid + 1)) != 0) {
int i = 25; /* an arbitrary number */
@@ -877,7 +909,7 @@ int kgdb_handle_exception(int ex_vector,
udelay(1);
}
- atomic_set(&kgdb_sync_softlockup[smp_processor_id()], 1);
+ atomic_set(&kgdb_sync_softlockup[raw_smp_processor_id()], 1);
/*
* Don't enter if the last instance of the exception handler wanted to
@@ -945,6 +977,7 @@ int kgdb_handle_exception(int ex_vector,
kgdb_deactivate_sw_breakpoints();
debugger_step = 0;
kgdb_contthread = NULL;
+ exception_level = 0;
if (kgdb_connected) {
/* If we're still unable to roundup all of the CPUs,
Index: linux-2.6.21.1/arch/i386/kernel/kgdb.c
===================================================================
--- linux-2.6.21.1.orig/arch/i386/kernel/kgdb.c
+++ linux-2.6.21.1/arch/i386/kernel/kgdb.c
@@ -302,6 +302,14 @@ int kgdb_skipexception(int exception, st
return 0;
}
+unsigned long kgdb_arch_pc(int exception, struct pt_regs *regs)
+{
+ if (exception == 3) {
+ return instruction_pointer(regs) - 1;
+ }
+ return instruction_pointer(regs);
+}
+
struct kgdb_arch arch_kgdb_ops = {
.gdb_bpt_instr = {0xcc},
.flags = KGDB_HW_BREAKPOINT,
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