From e0e53db6133c32964fd17f20b17073a402f07ed3 Mon Sep 17 00:00:00 2001 From: "K.Prasad" Date: Thu, 28 Jan 2010 16:44:15 +0530 Subject: [PATCH] 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 Cc: Ingo Molnar Cc: Roland McGrath Cc: Alan Stern Cc: Jan Kiszka LKML-Reference: <20100128111415.GC13935@in.ibm.com> Signed-off-by: Frederic Weisbecker --- arch/x86/kernel/hw_breakpoint.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) diff --git a/arch/x86/kernel/hw_breakpoint.c b/arch/x86/kernel/hw_breakpoint.c index 05d5fec64a94..ae90b4739435 100644 --- a/arch/x86/kernel/hw_breakpoint.c +++ b/arch/x86/kernel/hw_breakpoint.c @@ -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); -- 2.20.1