Re: [Kgdb-bugreport] [PATCH] attempt fix up breakpoint on reenter to KGDB
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Re: [Kgdb-bugreport] [PATCH] attempt fix up breakpoint on reenter to KGDB
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From: Pete/Piet D. <pe...@bl...> - 2007-05-15 07:32:38
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Jason Wessel wrote:
> If there are no objections, I will commit the following patch.
Sounds great to me; avoiding spin locks() is a hassle.
Ever noticed a problem with kgdb surviving a weekend of non-use?
I hit a breakpoint on Saturday and hoped to continue looking at it
today but the kgdb-stub, as usual, got out of phase and I had
to re-do the test that caused the breakpoint; I've seen it happen
many times.
- -piet
>
> --
>
> 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 <jas...@wi...>
>
> ---
> 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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