Re: [PATCH] [kgdb] Switch master cpu after gdb thread command for SMP (v3)

[Sonic Zhang]

Hi Jason,

Does this patch applied on your developing tree well? Any comments?

Thanks

Sonic

On Wed, Oct 22, 2008 at 4:40 PM, sonic zhang <sonic.adi@xxxxxxxxx> wrote:
>   In blackfin SMP architecture, different core has its own L1 SRAM and MMR
>   memory, which code running on the other core can't access. In current kgdb
>   impelemntation, cpus are represented by thread with minus prefix.
>
> If user run thread command in gdb to switch to the thread of the other cpu,
> kgdb should:
> 1. send IPI signal to master cpu
> 2. release the specific passive cpu waiting in IPI handler
> 3. exit kgdb exception loop on master cpu and trap into kgdb wait in IPI handler
> 4. trap the released passive cpu into kgdb exception in IPI handler
>
> Signed-off-by: Sonic Zhang <sonic.adi@xxxxxxxxx>
> ---
>  include/linux/kgdb.h |   16 +++++++++++-
>  kernel/kgdb.c        |   66 +++++++++++++++++++++++++++++++++++++++++++-------
>  2 files changed, 72 insertions(+), 10 deletions(-)
>
> diff --git a/include/linux/kgdb.h b/include/linux/kgdb.h
> index 6adcc29..664e396 100644
> --- a/include/linux/kgdb.h
> +++ b/include/linux/kgdb.h
> @@ -106,7 +106,8 @@ struct kgdb_bkpt {
>  # define KGDB_MAX_BREAKPOINTS  1000
>  #endif
>
> -#define KGDB_HW_BREAKPOINT     1
> +#define KGDB_HW_BREAKPOINT     0x1
> +#define KGDB_THR_PROC_SWAP     0x2
>
>  /*
>  * Functions each KGDB-supporting architecture must provide:
> @@ -203,6 +204,19 @@ kgdb_arch_handle_exception(int vector, int signo, int err_code,
>  */
>  extern void kgdb_roundup_cpus(unsigned long flags);
>
> +/**
> + *     kgdb_roundup_cpu - Get spcific CPU into a holding pattern
> + *     @cpu: Specific cpu id
> + *     @flags: Current IRQ state
> + *
> + *     On SMP systems, we need to switch cpu from current active one to
> + *     the other passive one. This get current active CPU into a known state
> + *     in kgdb_wait().
> + *
> + *     On non-SMP systems, this is not called.
> + */
> +extern void kgdb_roundup_cpu(int cpu, unsigned long flags);
> +
>  /* Optional functions. */
>  extern int kgdb_validate_break_address(unsigned long addr);
>  extern int kgdb_arch_set_breakpoint(unsigned long addr, char *saved_instr);
> diff --git a/kernel/kgdb.c b/kernel/kgdb.c
> index e4dcfb2..277986d 100644
> --- a/kernel/kgdb.c
> +++ b/kernel/kgdb.c
> @@ -565,6 +565,7 @@ static void kgdb_wait(struct pt_regs *regs)
>  {
>        unsigned long flags;
>        int cpu;
> +       struct task_struct *thread;
>
>        local_irq_save(flags);
>        cpu = raw_smp_processor_id();
> @@ -577,6 +578,8 @@ static void kgdb_wait(struct pt_regs *regs)
>        smp_wmb();
>        atomic_set(&cpu_in_kgdb[cpu], 1);
>
> +       kgdb_disable_hw_debug(regs);
> +
>        /* Wait till primary CPU is done with debugging */
>        while (atomic_read(&passive_cpu_wait[cpu]))
>                cpu_relax();
> @@ -584,6 +587,16 @@ static void kgdb_wait(struct pt_regs *regs)
>        kgdb_info[cpu].debuggerinfo = NULL;
>        kgdb_info[cpu].task = NULL;
>
> +       /* Trap into kgdb as the active CPU if gdb asks to switch. */
> +       thread = getthread(regs, -raw_smp_processor_id() - 2);
> +       if ((arch_kgdb_ops.flags & KGDB_THR_PROC_SWAP) &&
> +               kgdb_contthread && kgdb_contthread == thread) {
> +               kgdb_breakpoint();
> +               clocksource_touch_watchdog();
> +               local_irq_restore(flags);
> +               return;
> +       }
> +
>        /* fix up hardware debug registers on local cpu */
>        if (arch_kgdb_ops.correct_hw_break)
>                arch_kgdb_ops.correct_hw_break();
> @@ -1066,13 +1079,16 @@ static void gdb_cmd_query(struct kgdb_state *ks)
>                        sprintf(tmpstr, "shadowCPU%d",
>                                        (int)(-ks->threadid - 2));
>                        kgdb_mem2hex(tmpstr, remcom_out_buffer, strlen(tmpstr));
> +
> +                       if (arch_kgdb_ops.flags & KGDB_THR_PROC_SWAP)
> +                               ks->thr_query = 1;
>                }
>                break;
>        }
>  }
>
>  /* Handle the 'H' task query packets */
> -static void gdb_cmd_task(struct kgdb_state *ks)
> +static int gdb_cmd_task(struct kgdb_state *ks)
>  {
>        struct task_struct *thread;
>        char *ptr;
> @@ -1089,6 +1105,15 @@ static void gdb_cmd_task(struct kgdb_state *ks)
>                kgdb_usethread = thread;
>                ks->kgdb_usethreadid = ks->threadid;
>                strcpy(remcom_out_buffer, "OK");
> +#ifdef CONFIG_SMP
> +               if ((arch_kgdb_ops.flags & KGDB_THR_PROC_SWAP) &&
> +                       !ks->thr_query && ks->kgdb_usethreadid < -1 &&
> +                       - ks->kgdb_usethreadid - 2 != raw_smp_processor_id()) {
> +                       kgdb_roundup_cpu(raw_smp_processor_id(), 0);
> +                       kgdb_contthread = kgdb_usethread;
> +                       return 1;
> +               }
> +#endif
>                break;
>        case 'c':
>                ptr = &remcom_in_buffer[2];
> @@ -1106,6 +1131,8 @@ static void gdb_cmd_task(struct kgdb_state *ks)
>                strcpy(remcom_out_buffer, "OK");
>                break;
>        }
> +
> +       return 0;
>  }
>
>  /* Handle the 'T' thread query packets */
> @@ -1114,6 +1141,9 @@ static void gdb_cmd_thread(struct kgdb_state *ks)
>        char *ptr = &remcom_in_buffer[1];
>        struct task_struct *thread;
>
> +       if (arch_kgdb_ops.flags & KGDB_THR_PROC_SWAP)
> +               ks->thr_query = 0;
> +
>        kgdb_hex2long(&ptr, &ks->threadid);
>        thread = getthread(ks->linux_regs, ks->threadid);
>        if (thread)
> @@ -1223,7 +1253,12 @@ static int gdb_serial_stub(struct kgdb_state *ks)
>        /* Clear the out buffer. */
>        memset(remcom_out_buffer, 0, sizeof(remcom_out_buffer));
>
> -       if (kgdb_connected) {
> +       if ((arch_kgdb_ops.flags & KGDB_THR_PROC_SWAP) && kgdb_contthread) {
> +               remcom_out_buffer[0] = 'O';
> +               remcom_out_buffer[1] = 'K';
> +               remcom_out_buffer[2] = 0;
> +               put_packet(remcom_out_buffer);
> +       } else if (kgdb_connected) {
>                unsigned char thref[8];
>                char *ptr;
>
> @@ -1238,6 +1273,7 @@ static int gdb_serial_stub(struct kgdb_state *ks)
>                put_packet(remcom_out_buffer);
>        }
>
> +       kgdb_contthread = current;
>        kgdb_usethread = kgdb_info[ks->cpu].task;
>        ks->kgdb_usethreadid = shadow_pid(kgdb_info[ks->cpu].task->pid);
>        ks->pass_exception = 0;
> @@ -1284,7 +1320,8 @@ static int gdb_serial_stub(struct kgdb_state *ks)
>                        gdb_cmd_query(ks);
>                        break;
>                case 'H': /* task related */
> -                       gdb_cmd_task(ks);
> +                       if (gdb_cmd_task(ks))
> +                               goto kgdb_exit;
>                        break;
>                case 'T': /* Query thread status */
>                        gdb_cmd_thread(ks);
> @@ -1324,6 +1361,7 @@ default_handle:
>                        if (error >= 0 || remcom_in_buffer[0] == 'D' ||
>                            remcom_in_buffer[0] == 'k') {
>                                error = 0;
> +                               kgdb_contthread = NULL;
>                                goto kgdb_exit;
>                        }
>
> @@ -1464,11 +1502,15 @@ acquirelock:
>         * Get the passive CPU lock which will hold all the non-primary
>         * CPU in a spin state while the debugger is active
>         */
> -       if (!kgdb_single_step) {
> +       if (!kgdb_single_step && !kgdb_contthread) {
>                for (i = 0; i < NR_CPUS; i++)
>                        atomic_set(&passive_cpu_wait[i], 1);
>        }
>
> +       if (kgdb_contthread)
> +               atomic_set(&passive_cpu_wait[raw_smp_processor_id()], 1);
> +
> +
>        /*
>         * spin_lock code is good enough as a barrier so we don't
>         * need one here:
> @@ -1477,7 +1519,7 @@ acquirelock:
>
>  #ifdef CONFIG_SMP
>        /* Signal the other CPUs to enter kgdb_wait() */
> -       if ((!kgdb_single_step) && kgdb_do_roundup)
> +       if ((!kgdb_single_step && !kgdb_contthread) && kgdb_do_roundup)
>                kgdb_roundup_cpus(flags);
>  #endif
>
> @@ -1496,7 +1538,6 @@ acquirelock:
>        kgdb_post_primary_code(ks->linux_regs, ks->ex_vector, ks->err_code);
>        kgdb_deactivate_sw_breakpoints();
>        kgdb_single_step = 0;
> -       kgdb_contthread = current;
>        exception_level = 0;
>
>        /* Talk to debugger with gdbserial protocol */
> @@ -1510,7 +1551,14 @@ acquirelock:
>        kgdb_info[ks->cpu].task = NULL;
>        atomic_set(&cpu_in_kgdb[ks->cpu], 0);
>
> -       if (!kgdb_single_step) {
> +#ifdef CONFIG_SMP
> +       i = -(ks->kgdb_usethreadid + 2);
> +       if ((arch_kgdb_ops.flags & KGDB_THR_PROC_SWAP) &&
> +               kgdb_contthread && i != cpu) {
> +               atomic_set(&passive_cpu_wait[i], 0);
> +       }
> +#endif
> +       if (!kgdb_single_step && !kgdb_contthread) {
>                for (i = NR_CPUS-1; i >= 0; i--)
>                        atomic_set(&passive_cpu_wait[i], 0);
>                /*
> @@ -1536,9 +1584,9 @@ kgdb_restore:
>  int kgdb_nmicallback(int cpu, void *regs)
>  {
>  #ifdef CONFIG_SMP
> -       if (!atomic_read(&cpu_in_kgdb[cpu]) &&
> +       if (!atomic_read(&cpu_in_kgdb[cpu]) && (kgdb_contthread ||
>                        atomic_read(&kgdb_active) != cpu &&
> -                       atomic_read(&cpu_in_kgdb[atomic_read(&kgdb_active)])) {
> +                       atomic_read(&cpu_in_kgdb[atomic_read(&kgdb_active)]))) {
>                kgdb_wait((struct pt_regs *)regs);
>                return 0;
>        }
> --
> 1.6.0
>
>
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