[PATCH 092/105] hw_breakpoint: Fix cpu check in task_bp_pinned(cpu)

[Kamal Mostafa]

3.8.13.4 -stable review patch.  If anyone has any objections, please let me know.

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

From: Oleg Nesterov <oleg at redhat.com>

commit 8b4d801b2b123b6c09742f861fe44a8527b84d47 upstream.

trinity fuzzer triggered WARN_ONCE("Can't find any breakpoint
slot") in arch_install_hw_breakpoint() but the problem is not
arch-specific.

The problem is, task_bp_pinned(cpu) checks "cpu == iter->cpu"
but this doesn't account the "all cpus" events with iter->cpu <
0.

This means that, say, register_user_hw_breakpoint(tsk) can
happily create the arbitrary number > HBP_NUM of breakpoints
which can not be activated. toggle_bp_task_slot() is equally
wrong by the same reason and nr_task_bp_pinned[] can have
negative entries.

Simple test:

	# perl -e 'sleep 1 while 1' &
	# perf record -e mem:0x10,mem:0x10,mem:0x10,mem:0x10,mem:0x10 -p `pidof perl`

Before this patch this triggers the same problem/WARN_ON(),
after the patch it correctly fails with -ENOSPC.

Reported-by: Vince Weaver <vincent.weaver at maine.edu>
Signed-off-by: Oleg Nesterov <oleg at redhat.com>
Acked-by: Frederic Weisbecker <fweisbec at gmail.com>
Link: http://lkml.kernel.org/r/20130620155006.GA6324@redhat.com
Signed-off-by: Ingo Molnar <mingo at kernel.org>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 kernel/events/hw_breakpoint.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/events/hw_breakpoint.c b/kernel/events/hw_breakpoint.c
index fe8a916..4a99beb 100644
--- a/kernel/events/hw_breakpoint.c
+++ b/kernel/events/hw_breakpoint.c
@@ -120,7 +120,7 @@ static int task_bp_pinned(int cpu, struct perf_event *bp, enum bp_type_idx type)
 	list_for_each_entry(iter, &bp_task_head, hw.bp_list) {
 		if (iter->hw.bp_target == tsk &&
 		    find_slot_idx(iter) == type &&
-		    cpu == iter->cpu)
+		    (iter->cpu < 0 || cpu == iter->cpu))
 			count += hw_breakpoint_weight(iter);
 	}
 
-- 
1.8.1.2