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authorK.Prasad <prasad@linux.vnet.ibm.com>2010-01-28 16:44:15 +0530
committerFrederic Weisbecker <fweisbec@gmail.com>2010-01-29 02:44:30 +0100
commite0e53db6133c32964fd17f20b17073a402f07ed3 (patch)
tree72daeb1abb53901a0c8c10cbff234b5c4f9521c0
parent40f9249a73f6c251adea492b1c3d19d39e2a9bda (diff)
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>
-rw-r--r--arch/x86/kernel/hw_breakpoint.c10
1 files changed, 7 insertions, 3 deletions
diff --git a/arch/x86/kernel/hw_breakpoint.c b/arch/x86/kernel/hw_breakpoint.c
index 05d5fec64a9..ae90b473943 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);