Re: [PATCH 07/11 v3] livepatch: Trigger WARNING if livepatch function fails due to recursion

[Miroslav Benes]

On Thu, 5 Nov 2020, Steven Rostedt wrote:

> From: "Steven Rostedt (VMware)" 
> 
> If for some reason a function is called that triggers the recursion
> detection of live patching, trigger a warning. By not executing the live
> patch code, it is possible that the old unpatched function will be called
> placing the system into an unknown state.
> 
> Link: https://lore.kernel.org/r/20201029145709.GD16774@alley
> 
> Cc: Josh Poimboeuf 
> Cc: Jiri Kosina 
> Cc: Joe Lawrence 
> Cc: live-patch...@vger.kernel.org
> Suggested-by: Miroslav Benes 
> Reviewed-by: Petr Mladek 
> Signed-off-by: Steven Rostedt (VMware) 

Acked-by: Miroslav Benes 

> ---
> Changes since v2:
> 
>  - Blame Miroslav instead of Petr ;-)

Thanks. Fortunately, if printk is broken in WARN_ON_ONCE(), I can always 
blame Petr again :)

M

[PATCH 07/11 v3] livepatch: Trigger WARNING if livepatch function fails due to recursion

[VMware]

From: "Steven Rostedt (VMware)" 

If for some reason a function is called that triggers the recursion
detection of live patching, trigger a warning. By not executing the live
patch code, it is possible that the old unpatched function will be called
placing the system into an unknown state.

Link: https://lore.kernel.org/r/20201029145709.GD16774@alley

Cc: Josh Poimboeuf 
Cc: Jiri Kosina 
Cc: Joe Lawrence 
Cc: live-patch...@vger.kernel.org
Suggested-by: Miroslav Benes 
Reviewed-by: Petr Mladek 
Signed-off-by: Steven Rostedt (VMware) 
---
Changes since v2:

 - Blame Miroslav instead of Petr ;-)

 kernel/livepatch/patch.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/livepatch/patch.c b/kernel/livepatch/patch.c
index 6c0164d24bbd..15480bf3ce88 100644
--- a/kernel/livepatch/patch.c
+++ b/kernel/livepatch/patch.c
@@ -50,7 +50,7 @@ static void notrace klp_ftrace_handler(unsigned long ip,
ops = container_of(fops, struct klp_ops, fops);
 
bit = ftrace_test_recursion_trylock();
-   if (bit < 0)
+   if (WARN_ON_ONCE(bit < 0))
return;
/*
 * A variant of synchronize_rcu() is used to allow patching functions
-- 
2.28.0