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SubjectRe: [RFC Patch 2/2][Bugfix][x86][hw-breakpoint] Fix return-code to notifier chain in hw_breakpoint_handler
On Sat, Dec 26, 2009 at 11:58:33PM +0530, K.Prasad wrote:
> The hw-breakpoint handler will return NOTIFY_DONE for user-space breakpoints
> to generate SIGTRAP signal (and not for kernel-space addresses).
>
> Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
> ---
> arch/x86/kernel/hw_breakpoint.c | 9 +++++++--
> 1 file changed, 7 insertions(+), 2 deletions(-)
>
> Index: linux-2.6-tip/arch/x86/kernel/hw_breakpoint.c
> ===================================================================
> --- linux-2.6-tip.orig/arch/x86/kernel/hw_breakpoint.c
> +++ linux-2.6-tip/arch/x86/kernel/hw_breakpoint.c
> @@ -502,8 +502,6 @@ static int __kprobes hw_breakpoint_handl
> rcu_read_lock();
>
> bp = per_cpu(bp_per_reg[i], cpu);
> - if (bp)
> - rc = NOTIFY_DONE;
> /*
> * Reset the 'i'th TRAP bit in dr6 to denote completion of
> * exception handling
> @@ -517,6 +515,13 @@ static int __kprobes hw_breakpoint_handl
> rcu_read_unlock();
> break;
> }
> + /*
> + * Further processing in do_debug() is needed for a) user-space
> + * breakpoints (to generate signals) and b) when the system has
> + * taken exception due to multiple causes
> + */
> + if (bp->attr.bp_addr < TASK_SIZE)
> + rc = NOTIFY_DONE;
>
> perf_bp_event(bp, args->regs);
>
>


Looks good. This stops any further checks though. This
is fine in case we have the DR_STEP bit as we will
toggle to NOTIFY_DONE. But what about vm86 case? Is it
possible we might still have something to handle in this
side? (although I don't quite understand how we can have
a breakpoint triggered in vm86 mode).



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