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SubjectRe: [PATCH] livepatch: Convert error about unsupported reliable stacktrace into a warning
On Thu, Apr 18, 2019 at 01:29:36PM +0200, Petr Mladek wrote:
> The commit d0807da78e11d46f ("livepatch: Remove immediate feature") caused
> that any livepatch was refused when reliable stacktraces were not supported
> on the given architecture.
>
> The limitation is too strong. User space processes are safely migrated
> even when entering or leaving the kernel. Kthreads transition would
> need to get forced. But it is safe when:
>
> + The livepatch does not change the semantic of the code.
> + Callbacks do not depend on a safely finished transition.
>
> Suggested-by: Josh Poimboeuf <jpoimboe@redhat.com>
> Signed-off-by: Petr Mladek <pmladek@suse.com>
> ---
> kernel/livepatch/core.c | 5 ++---
> 1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
> index eb0ee10a1981..14f33ab6c583 100644
> --- a/kernel/livepatch/core.c
> +++ b/kernel/livepatch/core.c
> @@ -1003,11 +1003,10 @@ int klp_enable_patch(struct klp_patch *patch)
> return -ENODEV;
>
> if (!klp_have_reliable_stack()) {
> - pr_err("This architecture doesn't have support for the livepatch consistency model.\n");
> - return -EOPNOTSUPP;
> + pr_warn("This architecture doesn't have support for the livepatch consistency model.\n");
> + pr_warn("The livepatch transition may never complete.\n");
> }
>
> -
> mutex_lock(&klp_mutex);
>
> ret = klp_init_patch_early(patch);

Thanks Petr. I would also suggest that we remove the WARN_ONCE() from
the weak version of save_stack_trace_tsk_reliable(), since we expect it
to be used in this case.

--
Josh

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