linux-kernel - [PATCH 3.16 126/212] powerpc/xmon: Fix data-breakpoint

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Message-ID: <lsq.1496331796.714660311@decadent.org.uk>
Date:   Thu, 01 Jun 2017 16:43:16 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Michael Ellerman" <mpe@...erman.id.au>,
        "Ravi Bangoria" <ravi.bangoria@...ux.vnet.ibm.com>
Subject: [PATCH 3.16 126/212] powerpc/xmon: Fix data-breakpoint

3.16.44-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>

commit c21a493a2b44650707d06741601894329486f2ad upstream.

Currently xmon data-breakpoint feature is broken.

Whenever there is a watchpoint match occurs, hw_breakpoint_handler will
be called by do_break via notifier chains mechanism. If watchpoint is
registered by xmon, hw_breakpoint_handler won't find any associated
perf_event and returns immediately with NOTIFY_STOP. Similarly, do_break
also returns without notifying to xmon.

Solve this by returning NOTIFY_DONE when hw_breakpoint_handler does not
find any perf_event associated with matched watchpoint, rather than
NOTIFY_STOP, which tells the core code to continue calling the other
breakpoint handlers including the xmon one.

Signed-off-by: Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@...erman.id.au>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 arch/powerpc/kernel/hw_breakpoint.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/arch/powerpc/kernel/hw_breakpoint.c
+++ b/arch/powerpc/kernel/hw_breakpoint.c
@@ -227,8 +227,10 @@ int __kprobes hw_breakpoint_handler(stru
 	rcu_read_lock();

 	bp = __get_cpu_var(bp_per_reg);
-	if (!bp)
+	if (!bp) {
+		rc = NOTIFY_DONE;
 		goto out;
+	}
 	info = counter_arch_bp(bp);

 	/*