[PATCH 3.2 102/164] tracing/syscalls: Fix perf syscall tracing when syscall_nr == -1

[Ben Hutchings]

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

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

From: Will Deacon <will.deacon@xxxxxxx>

commit 60916a9382e88fbf5e54fd36a3e658efd7ab7bed upstream.

syscall_get_nr can return -1 in the case that the task is not executing
a system call.

This patch fixes perf_syscall_{enter,exit} to check that the syscall
number is valid before using it as an index into a bitmap.

Link: http://lkml.kernel.org/r/1345137254-7377-1-git-send-email-will.deacon@xxxxxxx

Cc: Jason Baron <jbaron@xxxxxxxxxx>
Cc: Wade Farnsworth <wade_farnsworth@xxxxxxxxxx>
Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Signed-off-by: Will Deacon <will.deacon@xxxxxxx>
Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 kernel/trace/trace_syscalls.c | 4 ++++
 1 file changed, 4 insertions(+)

--- a/kernel/trace/trace_syscalls.c
+++ b/kernel/trace/trace_syscalls.c
@@ -519,6 +519,8 @@ static void perf_syscall_enter(void *ign
 	int size;
 
 	syscall_nr = syscall_get_nr(current, regs);
+	if (syscall_nr < 0)
+		return;
 	if (!test_bit(syscall_nr, enabled_perf_enter_syscalls))
 		return;
 
@@ -593,6 +595,8 @@ static void perf_syscall_exit(void *igno
 	int size;
 
 	syscall_nr = syscall_get_nr(current, regs);
+	if (syscall_nr < 0)
+		return;
 	if (!test_bit(syscall_nr, enabled_perf_exit_syscalls))
 		return;
 

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