Commit e0e53db6 authored Jan 28, 2010 by K.Prasad Committed by Frederic Weisbecker Jan 29, 2010

x86/hw-breakpoints: Optimize return code from notifier chain in hw_breakpoint_handler



Processing of debug exceptions in do_debug() can stop if it
originated from a hw-breakpoint exception by returning NOTIFY_STOP
in most cases.

But for certain cases such as:

a) user-space breakpoints with pending SIGTRAP signal delivery (as
in the case of ptrace induced breakpoints).

b) exceptions due to other causes than breakpoints

We will continue to process the exception by returning NOTIFY_DONE.

Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Roland McGrath <roland@redhat.com>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Jan Kiszka <jan.kiszka@siemens.com>
LKML-Reference: <20100128111415.GC13935@in.ibm.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>

parent 40f9249a

arch/x86/kernel/hw_breakpoint.c

+7 −3

Original line number	Diff line number	Diff line
		@@ -502,8 +502,6 @@ static int __kprobes hw_breakpoint_handler(struct die_args *args)
		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_handler(struct die_args *args)

		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);