[3.8] tracing: fixes

Ingo,

This is the same as the last git pull I made (tip/perf/urgent) but without the last patch, as there's some minor fixes required for that patch.

Thanks,

-- Steve

Please pull the latest tip/perf/urgent-2 tree, which can be found at:

git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace.git
tip/perf/urgent-2

Head SHA1: d417f1730039a7fe59b66c6ac04fdaf8d1cfa96f

Steven Rostedt (2):
ftrace: Be first to run code modification on modules
tracing: Fix sparse warning with is_signed_type() macro

----

 include/linux/ftrace_event.h |    2 +-
 kernel/trace/ftrace.c        |    2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

From: Steven Rostedt <[email protected]>

If some other kernel subsystem has a module notifier, and adds a kprobe to a ftrace mcount point (now that kprobes work on ftrace points), when the ftrace notifier runs it will fail and disable ftrace, as well as kprobes that are attached to ftrace points.

Here's the error:

 WARNING: at kernel/trace/ftrace.c:1618 ftrace_bug+0x239/0x280()
 Hardware name: Bochs
 Modules linked in: fat(+) stap_56d28a51b3fe546293ca0700b10bcb29__8059(F) nfsv4 auth_rpcgss nfs dns_resolver fscache xt_nat iptable_nat nf_conntrack_ipv4 nf_defrag_ipv4 nf_nat_ipv4 nf_nat nf_conntrack lockd sunrpc ppdev parport_pc parport microcode virtio_net i2c_piix4 drm_kms_helper ttm drm i2c_core [last unloaded: bid_shared]
 Pid: 8068, comm: modprobe Tainted: GF            3.7.0-0.rc8.git0.1.fc19.x86_64 #1
 Call Trace:
  [<ffffffff8105e70f>] warn_slowpath_common+0x7f/0xc0
  [<ffffffff81134106>] ? __probe_kernel_read+0x46/0x70
  [<ffffffffa0180000>] ? 0xffffffffa017ffff
  [<ffffffffa0180000>] ? 0xffffffffa017ffff
  [<ffffffff8105e76a>] warn_slowpath_null+0x1a/0x20
  [<ffffffff810fd189>] ftrace_bug+0x239/0x280
  [<ffffffff810fd626>] ftrace_process_locs+0x376/0x520
  [<ffffffff810fefb7>] ftrace_module_notify+0x47/0x50
  [<ffffffff8163912d>] notifier_call_chain+0x4d/0x70
  [<ffffffff810882f8>] __blocking_notifier_call_chain+0x58/0x80
  [<ffffffff81088336>] blocking_notifier_call_chain+0x16/0x20
  [<ffffffff810c2a23>] sys_init_module+0x73/0x220
  [<ffffffff8163d719>] system_call_fastpath+0x16/0x1b
 ---[ end trace 9ef46351e53bbf80 ]---
 ftrace failed to modify [<ffffffffa0180000>] init_once+0x0/0x20 [fat]
  actual: cc:bb:d2:4b:e1

A kprobe was added to the init_once() function in the fat module on load. But this happened before ftrace could have touched the code. As ftrace didn't run yet, the kprobe system had no idea it was a ftrace point and simply added a breakpoint to the code (0xcc in the cc:bb:d2:4b:e1).

Then when ftrace went to modify the location from a call to mcount/fentry into a nop, it didn't see a call op, but instead it saw the breakpoint op and not knowing what to do with it, ftrace shut itself down.

The solution is to simply give the ftrace module notifier the max priority. This should have been done regardless, as the core code ftrace modification also happens very early on in boot up. This makes the module modification closer to core modification.

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

index 51b7159..356bc2f 100644
@@ -3998,7 +3998,7 @@ static int ftrace_module_notify(struct notifier_block *self,
 
 struct notifier_block ftrace_module_nb = {
 	.notifier_call = ftrace_module_notify,
-	.priority = 0,
+	.priority = INT_MAX,	/* Run before anything that can use kprobes */
 };
 
 extern unsigned long __start_mcount_loc[];

1.7.10.4

Correct! Thank you for fix that.

Masami HIRAMATSU
IT Management Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: [email protected]

From: Steven Rostedt <[email protected]>

Sparse complains when is_signed_type() is used on a pointer. This macro is needed for the format output used for ftrace and perf, to know if a binary field is a signed type or not. The is_signed_type() macro is used against all fields that are recorded by events to automate the operation.

The problem sparse has is with the current way is_signed_type() works:

((type)-1 < 0)

If "type" is a poiner, than sparse does not like it being compared to an integer (zero). The simple fix is to just give zero the same type. The runtime result stays the same.

---
 include/linux/ftrace_event.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index 642928c..cc87955 100644
@@ -266,7 +266,7 @@ extern int trace_define_field(struct ftrace_event_call *call, const char *type,
 extern int trace_add_event_call(struct ftrace_event_call *call);
 extern void trace_remove_event_call(struct ftrace_event_call *call);
 
-#define is_signed_type(type)	(((type)(-1)) < 0)
+#define is_signed_type(type)	(((type)(-1)) < (type)0)
 
 int trace_set_clr_event(const char *system, const char *event, int set);
 

1.7.10.4