Re: [PATCH] powerpc: kernel/kgdb.c: fix memory leakage

[tiejun.chen]

On 02/08/2013 10:41 AM, Benjamin Herrenschmidt wrote:
> 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...


Actually booke already copy the thread_info when we enter the debug exception, 
and I will send a patch to do the same thing for book3e, so I also remove these 
copying action here then we're happy without these nasty stuff :)

Tiejun

> 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;
> > >   }

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/