[RFC Patch 2/2][Bugfix][x86][hw-breakpoint] Fix return-code tonotifier chain in hw_breakpoint_handler

[K.Prasad]

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@xxxxxxxxxxxxxxxxxx>
---
 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);
 

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