On Mon, May 06, 2019 at 07:40:32PM -0500, Josh Poimboeuf wrote: > 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 <[email protected]> > > --- > > 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.
BTW, if you agree with this approach then we can leave the WARN_ON_ONCE() in save_stack_trace_tsk_reliable() after all. -- Josh
