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SubjectRe: [PATCH 3/3] livepatch: Cleanup message handling in klp_try_switch_task()
On Wed, 24 Apr 2019, Petr Mladek wrote:

> WARN_ON_ONCE() could not be called safely under rq lock because
> of console deadlock issues. Fortunately, simple printk_deferred()
> is enough because the warning is printed from a well defined
> location and context.
>
> Also klp_try_switch_task() is called under klp_mutex.
> Therefore, the buffer for debug messages could be static.
>
> Signed-off-by: Petr Mladek <pmladek@suse.com>
> ---
> kernel/livepatch/transition.c | 19 ++++++++++++++-----
> 1 file changed, 14 insertions(+), 5 deletions(-)
>
> diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c
> index 9c89ae8b337a..e8183d18227f 100644
> --- a/kernel/livepatch/transition.c
> +++ b/kernel/livepatch/transition.c
> @@ -254,6 +254,7 @@ static int klp_check_stack_func(struct klp_func *func,
> static int klp_check_stack(struct task_struct *task, char *err_buf)
> {
> static unsigned long entries[MAX_STACK_ENTRIES];
> + static int enosys_warned;
> struct stack_trace trace;
> struct klp_object *obj;
> struct klp_func *func;
> @@ -263,8 +264,16 @@ static int klp_check_stack(struct task_struct *task, char *err_buf)
> trace.nr_entries = 0;
> trace.max_entries = MAX_STACK_ENTRIES;
> trace.entries = entries;
> +
> ret = save_stack_trace_tsk_reliable(task, &trace);
> - WARN_ON_ONCE(ret == -ENOSYS);
> + if (ret == -ENOSYS) {
> + if (!enosys_warned) {
> + printk_deferred(KERN_WARNING "%s: save_stack_trace_tsk_reliable() not supported on this architecture.\n",
> + __func__);
> + enosys_warned = 1;

... abusing the fact that you are also printk maintainer :) ... looking at
the above, wouldn't it make sense to introduce generic
printk_deferred_once() instead?

--
Jiri Kosina
SUSE Labs

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