On Thu, 2013-01-31 at 20:04 -0600, Jason Wessel wrote:
> > diff --git a/arch/powerpc/kernel/kgdb.c b/arch/powerpc/kernel/kgdb.c
> > index 8747447..5ca82cd 100644
> > --- a/arch/powerpc/kernel/kgdb.c
> > +++ b/arch/powerpc/kernel/kgdb.c
> > @@ -154,12 +154,12 @@ static int kgdb_handle_breakpoint(struct pt_regs
> > *regs)
> > static int kgdb_singlestep(struct pt_regs *regs)
> > {
> > struct thread_info *thread_info, *exception_thread_info;
> > - struct thread_info *backup_current_thread_info = \
> > - (struct thread_info *)kmalloc(sizeof(struct thread_info),
> > GFP_KERNEL);
> > + struct thread_info *backup_current_thread_info;
>
>
>
> Woh... This is definitely wrong. You have found a problem for sure,
> but this is not the right way to fix it.
>
> It is not a good idea to kmalloc while single stepping because you can
> hang the kernel if you single step any operation in kmalloc().
Ok. I applied the fix because it was obviously correct vs. the previous
version of the code (ie. the kmalloc was already there)
> I am in the process of going through all the kgdb mails from the last
> few months while I had been away from the project, so I didn't catch
> this one and I see it has upstream commit (fefd9e6f8). I'll submit
> another patch to fix this the right way and use a static variable.
> This is ok to use a static variable here because this is not something
> we can recursively call at a single CPU level.
But a static will be shared by all CPUs or do you mean a per-cpu one ?
> If Ben prefers we not burn the memory unless kgdb is active we can
> kmalloc / kfree the space we need at the time that kgdb is
> initialized. Else we can go with this patch you see below. We'll see
> what Ben desires.
What about the stack ? thread info isn't very big...
Cheers,
Ben.
> -----
> diff --git a/arch/powerpc/kernel/kgdb.c b/arch/powerpc/kernel/kgdb.c
> index a7bc752..bb12c8b 100644
> --- a/arch/powerpc/kernel/kgdb.c
> +++ b/arch/powerpc/kernel/kgdb.c
> @@ -151,15 +151,16 @@ static int kgdb_handle_breakpoint(struct pt_regs *regs)
> return 1;
> }
>
> +static struct thread_info kgdb_backup_thread_info[NR_CPUS];
> +
> static int kgdb_singlestep(struct pt_regs *regs)
> {
> struct thread_info *thread_info, *exception_thread_info;
> - struct thread_info *backup_current_thread_info;
> + int cpu = raw_smp_processor_id();
>
> if (user_mode(regs))
> return 0;
>
> - backup_current_thread_info = (struct thread_info
> *)kmalloc(sizeof(struct thread_info), GFP_KERNEL);
> /*
> * On Book E and perhaps other processors, singlestep is handled on
> * the critical exception stack. This causes current_thread_info()
> @@ -175,7 +176,7 @@ static int kgdb_singlestep(struct pt_regs *regs)
>
> if (thread_info != exception_thread_info) {
> /* Save the original current_thread_info. */
> - memcpy(backup_current_thread_info, exception_thread_info,
> sizeof *thread_info);
> + memcpy(&kgdb_backup_thread_info[cpu], exception_thread_info,
> sizeof *thread_info);
> memcpy(exception_thread_info, thread_info, sizeof *thread_info);
> }
>
> @@ -183,9 +184,8 @@ static int kgdb_singlestep(struct pt_regs *regs)
>
> if (thread_info != exception_thread_info)
> /* Restore current_thread_info lastly. */
> - memcpy(exception_thread_info, backup_current_thread_info,
> sizeof *thread_info);
> + memcpy(exception_thread_info, &kgdb_backup_thread_info[cpu],
> sizeof *thread_info);
>
> - kfree(backup_current_thread_info);
> return 1;
> }
>
>
> -----
>
>
> Thanks,
> Jason.
>
>
> >
> > if (user_mode(regs))
> > return 0;
> >
> > + backup_current_thread_info = (struct thread_info
> > *)kmalloc(sizeof(struct thread_info), GFP_KERNEL);
> > /*
> > * On Book E and perhaps other processors, singlestep is handled on
> > * the critical exception stack. This causes current_thread_info()
> > @@ -185,6 +185,7 @@ static int kgdb_singlestep(struct pt_regs *regs)
> > /* Restore current_thread_info lastly. */
> > memcpy(exception_thread_info, backup_current_thread_info,
> > sizeof *thread_info);
> >
> > + kfree(backup_current_thread_info);
> > return 1;
> > }
> >
> >
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