Jason,
This check
atomic_read(&cpu_doing_single_step) != -1
may result in a loss of debug events on other cpus
Changing it to
atomic_read(&cpu_doing_single_step) == raw_smp_processor_id()
corrects that problem
I see that you've checked in this change. Would you mind waiting for 24 hours
after posting a patch? Thanks.
-Amit
On Wednesday 16 May 2007 00:36, Jason Wessel wrote:
> If there are no objections, I'd like to apply this patch as it fixes a
> critical gap when using source stepping that calls a low level
> singlestep that steps the boundary from the kernel to the user space.
> It is particularly bad when this corner case kills "init" as you get an
> unexpected reboot.
>
> ---
>
> This patch is to fix another corner case where kgdb can pass a single
> step trap to user space which was intended for the kernel. Now a
> source level "next" which single steps over an iret instruction will
> cause KGDB to continue and print an error to the console, vs the
> unpredictable consequence of sending a trap to unsuspecting code in
> the user space (normally resulting in process termination).
>
> Signed-off-by: Jason Wessel <[EMAIL PROTECTED]>
>
> ---
> arch/i386/kernel/kgdb.c | 31 +++++++++++++++++++------------
> arch/x86_64/kernel/kgdb.c | 17 ++++++++++++-----
> 2 files changed, 31 insertions(+), 17 deletions(-)
>
> Index: linux-2.6.21-standard/arch/i386/kernel/kgdb.c
> ===================================================================
> --- linux-2.6.21-standard.orig/arch/i386/kernel/kgdb.c
> +++ linux-2.6.21-standard/arch/i386/kernel/kgdb.c
> @@ -222,7 +222,7 @@ int kgdb_arch_handle_exception(int e_vec
> if (remcom_in_buffer[0] == 's') {
> linux_regs->eflags |= TF_MASK;
> debugger_step = 1;
> - atomic_set(&cpu_doing_single_step,smp_processor_id());
> + atomic_set(&cpu_doing_single_step,raw_smp_processor_id());
> }
>
> asm volatile ("movl %%db6, %0\n":"=r" (dr6));
> @@ -255,22 +255,29 @@ static int kgdb_notify(struct notifier_b
>
> /* Bad memory access? */
> if (cmd == DIE_PAGE_FAULT_NO_CONTEXT && atomic_read(&debugger_active)
> - && kgdb_may_fault) {
> + && kgdb_may_fault) {
> kgdb_fault_longjmp(kgdb_fault_jmp_regs);
> return NOTIFY_STOP;
> } else if (cmd == DIE_PAGE_FAULT)
> /* A normal page fault, ignore. */
> return NOTIFY_DONE;
> - else if ((cmd == DIE_NMI || cmd == DIE_NMI_IPI ||
> - cmd == DIE_NMIWATCHDOG) && atomic_read(&debugger_active)) {
> - /* CPU roundup */
> - kgdb_nmihook(smp_processor_id(), regs);
> - return NOTIFY_STOP;
> - } else if (cmd == DIE_NMI_IPI || cmd == DIE_NMI ||
> user_mode(regs) ||
> - (cmd == DIE_DEBUG &&
> atomic_read(&debugger_active))) - /* Normal watchdog event or
> userspace debugging, or spurious - * debug exception,
> ignore. */
> - return NOTIFY_DONE;
> + else if ((cmd == DIE_NMI || cmd == DIE_NMI_IPI ||
> + cmd == DIE_NMIWATCHDOG) && atomic_read(&debugger_active)) {
> + /* CPU roundup */
> + kgdb_nmihook(raw_smp_processor_id(), regs);
> + return NOTIFY_STOP;
> + } else if (cmd == DIE_DEBUG && atomic_read(&cpu_doing_single_step)
> != -1
> + && user_mode(regs)) {
> + /* single step exception from kernel space to user space so
> + * eat the exception and continue the process
> + */
> + printk(KERN_ERR "KGDB: trap/step from kernel to user space,
> resuming...\n");
> + return NOTIFY_STOP;
> + } else if (cmd == DIE_NMI_IPI || cmd == DIE_NMI || user_mode(regs) ||
> + (cmd == DIE_DEBUG && atomic_read(&debugger_active)))
> + /* Normal watchdog event or userspace debugging, or spurious
> + * debug exception, ignore. */
> + return NOTIFY_DONE;
>
> kgdb_handle_exception(args->trapnr, args->signr, args->err, regs);
>
> Index: linux-2.6.21-standard/arch/x86_64/kernel/kgdb.c
> ===================================================================
> --- linux-2.6.21-standard.orig/arch/x86_64/kernel/kgdb.c
> +++ linux-2.6.21-standard/arch/x86_64/kernel/kgdb.c
> @@ -183,7 +183,7 @@ int kgdb_arch_handle_exception(int e_vec
> debugger_step = 1;
> if (kgdb_contthread)
> atomic_set(&cpu_doing_single_step,
> - smp_processor_id());
> + raw_smp_processor_id());
>
> }
>
> @@ -237,7 +237,7 @@ void kgdb_shadowinfo(struct pt_regs *reg
> static char intr_desc[] = "Stack at interrupt entrypoint";
> static char exc_desc[] = "Stack at exception entrypoint";
> struct pt_regs *stregs;
> - int cpu = smp_processor_id();
> + int cpu = raw_smp_processor_id();
>
> if ((stregs = in_interrupt_stack(regs->rsp, cpu)))
> kgdb_mem2hex(intr_desc, buffer, strlen(intr_desc));
> @@ -248,7 +248,7 @@ void kgdb_shadowinfo(struct pt_regs *reg
> struct task_struct *kgdb_get_shadow_thread(struct pt_regs *regs, int
> threadid)
> {
> struct pt_regs *stregs;
> - int cpu = smp_processor_id();
> + int cpu = raw_smp_processor_id();
>
> if ((stregs = in_interrupt_stack(regs->rsp, cpu)))
> return current;
> @@ -261,7 +261,7 @@ struct task_struct *kgdb_get_shadow_thre
> struct pt_regs *kgdb_shadow_regs(struct pt_regs *regs, int threadid)
> {
> struct pt_regs *stregs;
> - int cpu = smp_processor_id();
> + int cpu = raw_smp_processor_id();
>
> if ((stregs = in_interrupt_stack(regs->rsp, cpu)))
> return stregs;
> @@ -285,9 +285,16 @@ static int kgdb_notify(struct notifier_b
> return NOTIFY_STOP;
> /* CPU roundup? */
> } else if (atomic_read(&debugger_active) && cmd == DIE_NMI_IPI) {
> - kgdb_nmihook(smp_processor_id(), regs);
> + kgdb_nmihook(raw_smp_processor_id(), regs);
> return NOTIFY_STOP;
> /* See if KGDB is interested. */
> + } else if (cmd == DIE_DEBUG && atomic_read(&cpu_doing_single_step)
> != -1
> + && user_mode(regs)) {
> + /* single step exception from kernel space to user space so
> + * eat the exception and continue the process
> + */
> + printk(KERN_ERR "KGDB: trap/step from kernel to user space,
> resuming...\n");
> + return NOTIFY_STOP;
> } else if (cmd == DIE_PAGE_FAULT || user_mode(regs) ||
> cmd == DIE_NMI_IPI || (cmd == DIE_DEBUG &&
> atomic_read(&debugger_active)))
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