On Tue, Apr 30, 2019 at 11:10:48AM +0200, Petr Mladek wrote: > WARN_ON_ONCE() could not be called safely under rq lock because > of console deadlock issues. Fortunately, there is another check > for the reliable stacktrace support in klp_enable_patch(). > > Signed-off-by: Petr Mladek <pmladek@xxxxxxxx> > --- > kernel/livepatch/transition.c | 9 ++++++++- > 1 file changed, 8 insertions(+), 1 deletion(-) > > diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c > index 9c89ae8b337a..8e0274075e75 100644 > --- a/kernel/livepatch/transition.c > +++ b/kernel/livepatch/transition.c > @@ -263,8 +263,15 @@ 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); > + /* > + * pr_warn() under task rq lock might cause a deadlock. > + * Fortunately, missing reliable stacktrace support has > + * already been handled when the livepatch was enabled. > + */ > + if (ret == -ENOSYS) > + return ret; I find the comment to be a bit wordy and confusing (and vague). Also this check is effectively the same as the klp_have_reliable_stack() check which is done in kernel/livepatch/core.c. So I think it would be clearer and more consistent if the same check is done here: if (!klp_have_reliable_stack()) return -ENOSYS; ret = save_stack_trace_tsk_reliable(task, &trace); [ no need to check ret for ENOSYS here ] Then, IMO, no comment is needed. -- Josh
