Messages in this thread Patch in this message | | | Date | Tue, 18 Nov 2008 18:06:35 +0100 | From | Heiko Carstens <> | Subject | Re: ftrace: preemptoff selftest not working |
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On Tue, Nov 18, 2008 at 03:47:51PM +0100, Ingo Molnar wrote: > > * Steven Rostedt <rostedt@goodmis.org> wrote: > > > > > On Tue, 18 Nov 2008, Ingo Molnar wrote: > > > > > > * Steven Rostedt <rostedt@goodmis.org> wrote: > > > > > > > > Hence the trace buffer will be empty. The patch below makes the > > > > > selftests working for me, since then they run in preemptible > > > > > context. But it is ugly and I'm not proposing it for upstream ;) > > > > > > > > > > Just wanted to make you aware that there is a bug. > > > > > > > > Yep, this might be a better answer than what I put into linux-tip > > > > (and my git repo). > > > > > > > > See: > > > > > > > > ftrace: force pass of preemptoff selftest > > > > > > > > The cause of the bug was the conversion of the BKL back to a > > > > spinlock, and making it non preempt. The initcall code is called > > > > with the BKL applied which now means it can not preempt. This breaks > > > > the preempt tracer selftest. > > > > > > > > My solution was to just force a pass if this is detected. Perhaps > > > > moving the test might be better. > > > > > > it would be better to just drop the BKL in that selftest. (or in all > > > selftests - an elevated preempt count will skew a number of things) > > > > I have no problem with that, but does the BKL play any role for > > being held? I have no idea why it is taken in boot up, so I'm > > hestiant to touch it. > > we can drop it in selected initcalls just fine. Its only role is > old-style init functions racing with other async contexts of > themselves.
Something like below works fine for me...
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com> ---
kernel/trace/trace.c | 8 ++++++++ 1 file changed, 8 insertions(+)
Index: linux-2.6/kernel/trace/trace.c =================================================================== --- linux-2.6.orig/kernel/trace/trace.c +++ linux-2.6/kernel/trace/trace.c @@ -482,6 +482,13 @@ int register_tracer(struct tracer *type) } #ifdef CONFIG_FTRACE_STARTUP_TEST + /* + * When this gets called we hold the BKL which means that preemption + * is disabled. Various trace selftests however need to disable + * and enable preemption for successful tests. So we drop the BKL here + * and grab it after the tests again. + */ + unlock_kernel(); if (type->selftest) { struct tracer *saved_tracer = current_trace; struct trace_array *tr = &global_trace; @@ -515,6 +522,7 @@ int register_tracer(struct tracer *type) } printk(KERN_CONT "PASSED\n"); } + lock_kernel(); #endif type->next = trace_types;
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