Re: [Patch 02/12] Introducing generic hardware breakpoint handler interfaces

K.Prasad
2009-05-26T03:23:10Z

On Mon, May 25, 2009 at 08:36:36PM +0200, Frederic Weisbecker wrote:
> On Sat, May 16, 2009 at 05:55:52AM +0530, K.Prasad wrote:
> > This patch introduces the generic Hardware Breakpoint interfaces for both user
> > and kernel space requests.
> >
> > Original-patch-by: Alan Stern <stern@rowland.harvard.edu>
> > Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
> > Reviewed-by: Alan Stern <stern@rowland.harvard.edu>
> > ---
> > arch/Kconfig | 4
> > kernel/Makefile | 1
> > kernel/hw_breakpoint.c | 369 +++++++++++++++++++++++++++++++++++++++++++++++++
> > 3 files changed, 374 insertions(+)
> >
> > +/**
> > + * register_kernel_hw_breakpoint - register a hardware breakpoint for kernel space
> > + * @bp: the breakpoint structure to register
> > + *
> > + * @bp.info->name or @bp.info->address, @bp.info->len, @bp.info->type and
> > + * @bp->triggered must be set properly before invocation
> > + *
> > + */
> > +int register_kernel_hw_breakpoint(struct hw_breakpoint *bp)
> > +{
> > + int rc;
> > +
> > + rc = arch_validate_hwbkpt_settings(bp, NULL);
> > + if (rc)
> > + return rc;
> > +
> > + spin_lock_bh(&hw_breakpoint_lock);
> > +
> > + rc = -EINVAL;
> > + /* Check if we are over-committing */
> > + if ((hbp_kernel_pos > 0) && (!hbp_user_refcount[hbp_kernel_pos-1])) {
>
>
>
> If hbp_kernel_pos == 0, shouldn't it return -ENOSPC ?
> If several kernel users try to register a breakpoint, and there is no
> more room for one of them, then we know it has failed not because
> of an error in the breakpoint instance but because of a lack of
> resources.
>
> Frederic.
>

Agreed. It's done correctly in the case of register_user_hw_breakpoint()
but not here. Here's a tiny patch that corrects it.

Modify the return code in register_kernel_hw_breakpoint()

Modify the return code in register_kernel_hw_breakpoint() to return -ENOSPC
if we are error-returning due to lack of free HW breakpoint registers.

Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
---
kernel/hw_breakpoint.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

Index: linux-2.6-tip.hbkpt/kernel/hw_breakpoint.c
===================================================================
--- linux-2.6-tip.hbkpt.orig/kernel/hw_breakpoint.c
+++ linux-2.6-tip.hbkpt/kernel/hw_breakpoint.c
@@ -312,7 +312,7 @@ int register_kernel_hw_breakpoint(struct

spin_lock_bh(&hw_breakpoint_lock);

- rc = -EINVAL;
+ rc = -ENOSPC;
/* Check if we are over-committing */
if ((hbp_kernel_pos > 0) && (!hbp_user_refcount[hbp_kernel_pos-1])) {
hbp_kernel_pos--;