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.
--
Josh
