[Qemu-devel] [PATCH] gdbstub: do not restart crashed guest

[Qemu-devel] [PATCH] gdbstub: do not restart crashed guest

[Paolo Bonzini]

If a guest has crashed with an internal error or similar, detaching
gdb (or any other debugger action) should not restart it.

Cc: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 gdbstub.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/gdbstub.c b/gdbstub.c
index e80e1d3..90e54cb 100644
--- a/gdbstub.c
+++ b/gdbstub.c
@@ -371,7 +371,9 @@ static inline void gdb_continue(GDBState *s)
 #ifdef CONFIG_USER_ONLY
     s->running_state = 1;
 #else
-    vm_start();
+    if (runstate_check(RUN_STATE_DEBUG)) {
+        vm_start();
+    }
 #endif
 }
 
-- 
1.8.1.4

Re: [Qemu-devel] [PATCH] gdbstub: do not restart crashed guest

[Laszlo Ersek]

On 05/30/13 13:20, Paolo Bonzini wrote:
> If a guest has crashed with an internal error or similar, detaching
> gdb (or any other debugger action) should not restart it.
> 
> Cc: Jan Kiszka <jan.kiszka@siemens.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  gdbstub.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/gdbstub.c b/gdbstub.c
> index e80e1d3..90e54cb 100644
> --- a/gdbstub.c
> +++ b/gdbstub.c
> @@ -371,7 +371,9 @@ static inline void gdb_continue(GDBState *s)
>  #ifdef CONFIG_USER_ONLY
>      s->running_state = 1;
>  #else
> -    vm_start();
> +    if (runstate_check(RUN_STATE_DEBUG)) {
> +        vm_start();
> +    }
>  #endif
>  }
>  
> 

I sought to check the gdb_continue() call sites, and uses of
RUN_STATE_DEBUG. Seems reasonable.

Reviewed-by: Laszlo Ersek <lersek@redhat.com>

(
FWIW I wonder why in commit ad02b96a Luiz allowed DEBUG -> SUSPENDED. As
far as I understand, when the debugger is attached, the guest is not
running, hence it can't go directly to RUN_STATE_SUSPENDED. Maybe due to
a concurrent monitor command?

Technically it does seem possible; from main_loop_should_exit():

    if (qemu_debug_requested()) {
        vm_stop(RUN_STATE_DEBUG);
    }
    if (qemu_suspend_requested()) {
        qemu_system_suspend();
    }

Both requests could become pending during one iteration of the loop, and
the next iteration will see both of them. OK.
)

Laszlo

Re: [Qemu-devel] [PATCH] gdbstub: do not restart crashed guest

[Luiz Capitulino]

On Thu, 30 May 2013 13:55:50 +0200
Laszlo Ersek <lersek@redhat.com> wrote:

> On 05/30/13 13:20, Paolo Bonzini wrote:
> > If a guest has crashed with an internal error or similar, detaching
> > gdb (or any other debugger action) should not restart it.
> > 
> > Cc: Jan Kiszka <jan.kiszka@siemens.com>
> > Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> > ---
> >  gdbstub.c | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> > 
> > diff --git a/gdbstub.c b/gdbstub.c
> > index e80e1d3..90e54cb 100644
> > --- a/gdbstub.c
> > +++ b/gdbstub.c
> > @@ -371,7 +371,9 @@ static inline void gdb_continue(GDBState *s)
> >  #ifdef CONFIG_USER_ONLY
> >      s->running_state = 1;
> >  #else
> > -    vm_start();
> > +    if (runstate_check(RUN_STATE_DEBUG)) {
> > +        vm_start();
> > +    }
> >  #endif
> >  }
> >  
> > 
> 
> I sought to check the gdb_continue() call sites, and uses of
> RUN_STATE_DEBUG. Seems reasonable.
> 
> Reviewed-by: Laszlo Ersek <lersek@redhat.com>
> 
> (
> FWIW I wonder why in commit ad02b96a Luiz allowed DEBUG -> SUSPENDED. As
> far as I understand, when the debugger is attached, the guest is not
> running, hence it can't go directly to RUN_STATE_SUSPENDED. Maybe due to
> a concurrent monitor command?

I honestly don't remember if I took into account the explanation you gave
below. You're right that a stopped guest can't suspend.

> 
> Technically it does seem possible; from main_loop_should_exit():
> 
>     if (qemu_debug_requested()) {
>         vm_stop(RUN_STATE_DEBUG);
>     }
>     if (qemu_suspend_requested()) {
>         qemu_system_suspend();
>     }
> 
> Both requests could become pending during one iteration of the loop, and
> the next iteration will see both of them. OK.
> )
> 
> Laszlo
> 

Re: [Qemu-devel] [PATCH] gdbstub: do not restart crashed guest

[Anthony Liguori]

Applied.  Thanks.

Regards,

Anthony Liguori