[Patch 2/2 v2] Return proper code to notifier chain inhw_breakpoint_handler

[K.Prasad]

Processing of debug exceptions (in do_debug()) can stop if it originated from
a hw-breakpoint exception (return NOTIFY_STOP). For certain cases such as
a) user-space breakpoints with pending SIGTRAP signal delivery (as in the case
of ptrace induced breakpoints) and b) exceptions due to multiple causes (other
than breakpoints) we will continue to process the exception (by returning
NOTIFY_DONE).

Signed-off-by: K.Prasad <prasad@xxxxxxxxxxxxxxxxxx>
---
 arch/x86/kernel/hw_breakpoint.c |   10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

Index: linux-2.6-tip.bugfix_perf_hbkpt/arch/x86/kernel/hw_breakpoint.c
===================================================================
--- linux-2.6-tip.bugfix_perf_hbkpt.orig/arch/x86/kernel/hw_breakpoint.c
+++ linux-2.6-tip.bugfix_perf_hbkpt/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
@@ -522,7 +520,13 @@ static int __kprobes hw_breakpoint_handl
 
 		rcu_read_unlock();
 	}
-	if (dr6 & (~DR_TRAP_BITS))
+	/*
+	 * 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 ((current->thread.debugreg6 & DR_TRAP_BITS) ||
+	    (dr6 & (~DR_TRAP_BITS)))
 		rc = NOTIFY_DONE;
 
 	set_debugreg(dr7, 7);

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