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SubjectRe: [PATCH 1/2] ftrace: disable tracing on resize

Pekka,

I forgot to add you to the Cc list. Could you test this patch to see if it
fixes the bug you reported. It fixed a bug I was able to reproduce, but I
was never able to reproduce the exact same bug you have seen.

-- Steve


On Mon, 10 Nov 2008, Steven Rostedt wrote:

> Impact: fix for bug on resize
>
> This patch addresses the bug found here:
>
> http://bugzilla.kernel.org/show_bug.cgi?id=11996
>
> When ftrace converted to the new unified trace buffer, the resizing of
> the buffer was not protected as much as it was originally. If tracing
> is performed while the resize occurs, then the buffer can be corrupted.
>
> This patch disables all ftrace buffer modifications before a resize
> takes place.
>
> Signed-off-by: Steven Rostedt <srostedt@redhat.com>
> ---
> kernel/trace/trace.c | 17 ++++++++++++++++-
> 1 files changed, 16 insertions(+), 1 deletions(-)
>
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 9f3b478..abfa810 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -2676,7 +2676,7 @@ tracing_entries_write(struct file *filp, const char __user *ubuf,
> {
> unsigned long val;
> char buf[64];
> - int ret;
> + int ret, cpu;
> struct trace_array *tr = filp->private_data;
>
> if (cnt >= sizeof(buf))
> @@ -2704,6 +2704,14 @@ tracing_entries_write(struct file *filp, const char __user *ubuf,
> goto out;
> }
>
> + /* disable all cpu buffers */
> + for_each_tracing_cpu(cpu) {
> + if (global_trace.data[cpu])
> + atomic_inc(&global_trace.data[cpu]->disabled);
> + if (max_tr.data[cpu])
> + atomic_inc(&max_tr.data[cpu]->disabled);
> + }
> +
> if (val != global_trace.entries) {
> ret = ring_buffer_resize(global_trace.buffer, val);
> if (ret < 0) {
> @@ -2735,6 +2743,13 @@ tracing_entries_write(struct file *filp, const char __user *ubuf,
> if (tracing_disabled)
> cnt = -ENOMEM;
> out:
> + for_each_tracing_cpu(cpu) {
> + if (global_trace.data[cpu])
> + atomic_dec(&global_trace.data[cpu]->disabled);
> + if (max_tr.data[cpu])
> + atomic_dec(&max_tr.data[cpu]->disabled);
> + }
> +
> max_tr.entries = global_trace.entries;
> mutex_unlock(&trace_types_lock);
>
> --
> 1.5.6.5
>
> --
>
>


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