hw_breakpoint: Fix cpu check in task_bp_pinned( cpu)

Commit-ID:  8b4d801b2b123b6c09742f861fe44a8527b84d47
Gitweb:     http://git.kernel.org/tip/8b4d801b2b123b6c09742f861fe44a8527b84d47
Author:     Oleg Nesterov <[email protected]>
AuthorDate: Thu, 20 Jun 2013 17:50:06 +0200
Committer:  Ingo Molnar <[email protected]>
CommitDate: Thu, 20 Jun 2013 17:57:00 +0200

hw_breakpoint: Fix cpu check in task_bp_pinned(cpu)

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.

---
 kernel/events/hw_breakpoint.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index a64f8ae..a853dea 100644
@@ -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);
 	}