linux-kernel - [PATCH] livepatch: Convert error about unsupported reliable stacktrace into a warning

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Message-Id: <20190418112936.13295-1-pmladek@suse.com>
Date:   Thu, 18 Apr 2019 13:29:36 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Jiri Kosina <jikos@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Miroslav Benes <mbenes@...e.cz>
Cc:     Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        live-patching@...r.kernel.org, linux-kernel@...r.kernel.org,
        Petr Mladek <pmladek@...e.com>
Subject: [PATCH] livepatch: Convert error about unsupported reliable stacktrace into a warning

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@...hat.com>
Signed-off-by: Petr Mladek <pmladek@...e.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);
-- 
2.16.4