path: root/kernel/trace/trace_sched_wakeup.c
diff options
authorSteven Rostedt <srostedt@redhat.com>2009-04-03 11:12:23 -0400
committerIngo Molnar <mingo@elte.hu>2009-04-07 13:58:54 +0200
commit301fd748e2c81e78e74edbc694a64caa7b95dda2 (patch)
tree563f5e7796b451fbefb49fa441f18374a4a761a1 /kernel/trace/trace_sched_wakeup.c
parenta053958f073740219df1da596b42bfefdab634c4 (diff)
tracing: remove CALLER_ADDR2 from wakeup tracer
Maneesh Soni was getting a crash when running the wakeup tracer. We debugged it down to the recording of the function with the CALLER_ADDR2 macro. This is used to get the location of the caller to schedule. But the problem comes when schedule is called by assmebly. In the case that Maneesh had, retint_careful would call schedule. But retint_careful does not set up a proper frame pointer. CALLER_ADDR2 is defined as __builtin_return_address(2). This produces the following assembly in the wakeup tracer code. mov 0x0(%rbp),%rcx <--- get the frame pointer of the caller mov %r14d,%r8d mov 0xf2de8e(%rip),%rdi mov 0x8(%rcx),%rsi <-- this is __builtin_return_address(1) mov 0x28(%rdi,%rax,8),%rbx mov (%rcx),%rax <-- get the frame pointer of the caller's caller mov %r12,%rcx mov 0x8(%rax),%rdx <-- this is __builtin_return_address(2) At the reading of 0x8(%rax) Maneesh's machine would take a fault. The reason is that retint_careful did not set up the return address and the content of %rax here was zero. To verify this, I sent Maneesh a patch to create a frame pointer in retint_careful. He ran the test again but this time he would take the same type of fault from sysret_careful. The retint_careful was no longer an issue, but there are other callers that still have issues. Instead of adding frame pointers for all callers to schedule (in possibly all archs), it is much safer to simply not use CALLER_ADDR2. This loses out on knowing what called schedule, but the function tracer will help there if needed. Reported-by: Maneesh Soni <maneesh@in.ibm.com> Signed-off-by: Steven Rostedt <rostedt@goodmis.org> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel/trace/trace_sched_wakeup.c')
1 files changed, 7 insertions, 1 deletions
diff --git a/kernel/trace/trace_sched_wakeup.c b/kernel/trace/trace_sched_wakeup.c
index 3c5ad6b2ec8..5bc00e8f153 100644
--- a/kernel/trace/trace_sched_wakeup.c
+++ b/kernel/trace/trace_sched_wakeup.c
@@ -154,7 +154,7 @@ probe_wakeup_sched_switch(struct rq *rq, struct task_struct *prev,
if (unlikely(!tracer_enabled || next != wakeup_task))
goto out_unlock;
- trace_function(wakeup_trace, CALLER_ADDR1, CALLER_ADDR2, flags, pc);
+ trace_function(wakeup_trace, CALLER_ADDR0, CALLER_ADDR1, flags, pc);
tracing_sched_switch_trace(wakeup_trace, prev, next, flags, pc);
@@ -257,6 +257,12 @@ probe_wakeup(struct rq *rq, struct task_struct *p, int success)
data = wakeup_trace->data[wakeup_cpu];
data->preempt_timestamp = ftrace_now(cpu);
tracing_sched_wakeup_trace(wakeup_trace, p, current, flags, pc);
+ /*
+ * We must be careful in using CALLER_ADDR2. But since wake_up
+ * is not called by an assembly function (where as schedule is)
+ * it should be safe to use it here.
+ */
trace_function(wakeup_trace, CALLER_ADDR1, CALLER_ADDR2, flags, pc);