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

> On Wed, Apr 24, 2019 at 10:55:50AM +0200, 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;
> > + }
> > + return ret;
> > + }
>
> We already have a similar printk in patch 1, so is this warning really
> needed?

I don't think so. pr_warn() in klp_enable_patch() should be enough in my
opinion.

However,

if (ret == -ENOSYS)
return ret;

would be justified, wouldn't it?

Miroslav

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