Revert "livepatch: Remove reliable stacktrace check in klp_try_switch_task()" [Linux 5.3]

This Linux kernel change "Revert “livepatch: Remove reliable stacktrace check in klp_try_switch_task()”" is included in the Linux 5.3 release. This change is authored by Miroslav Benes <mbenes [at]> on Tue Jun 11 16:13:19 2019 +0200. The commit for this change in Linux stable tree is 67059d6 (patch).

Revert "livepatch: Remove reliable stacktrace check in klp_try_switch_task()"

This reverts commit 1d98a69e5cef3aeb68bcefab0e67e342d6bb4dad. Commit
31adf2308f33 ("livepatch: Convert error about unsupported reliable
stacktrace into a warning") weakened the enforcement for architectures
to have reliable stack traces support. The system only warns now about

It only makes sense to reintroduce the compile time checking in
klp_try_switch_task() again and bail out early.

Signed-off-by: Miroslav Benes <>
Acked-by: Josh Poimboeuf <>
Reviewed-by: Kamalesh Babulal <>
Signed-off-by: Petr Mladek <>

There are 7 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.

 kernel/livepatch/transition.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c
index 0a3889c..cb85dae 100644
--- a/kernel/livepatch/transition.c
+++ b/kernel/livepatch/transition.c
@@ -306,6 +306,13 @@ static bool klp_try_switch_task(struct task_struct *task)
        return true;

+    * For arches which don't have reliable stack traces, we have to rely
+    * on other methods (e.g., switching tasks at kernel exit).
+    */
+   if (!klp_have_reliable_stack())
+       return false;
+   /*
     * Now try to check the stack for any to-be-patched or to-be-unpatched
     * functions.  If all goes well, switch the task to the target patch
     * state.

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