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Subject[for-next][PATCH 06/17] livepatch/ftrace: Add recursion protection to the ftrace callback
From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>

If a ftrace callback does not supply its own recursion protection and
does not set the RECURSION_SAFE flag in its ftrace_ops, then ftrace will
make a helper trampoline to do so before calling the callback instead of
just calling the callback directly.

The default for ftrace_ops is going to change. It will expect that handlers
provide their own recursion protection, unless its ftrace_ops states
otherwise.

Link: https://lkml.kernel.org/r/20201028115613.291169246@goodmis.org
Link: https://lkml.kernel.org/r/20201106023547.122802424@goodmis.org

Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Jiri Kosina <jikos@kernel.org>
Cc: Joe Lawrence <joe.lawrence@redhat.com>
Cc: live-patching@vger.kernel.org
Reviewed-by: Petr Mladek <pmladek@suse.com>
Acked-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
kernel/livepatch/patch.c | 5 +++++
1 file changed, 5 insertions(+)

diff --git a/kernel/livepatch/patch.c b/kernel/livepatch/patch.c
index b552cf2d85f8..6c0164d24bbd 100644
--- a/kernel/livepatch/patch.c
+++ b/kernel/livepatch/patch.c
@@ -45,9 +45,13 @@ static void notrace klp_ftrace_handler(unsigned long ip,
struct klp_ops *ops;
struct klp_func *func;
int patch_state;
+ int bit;

ops = container_of(fops, struct klp_ops, fops);

+ bit = ftrace_test_recursion_trylock();
+ if (bit < 0)
+ return;
/*
* A variant of synchronize_rcu() is used to allow patching functions
* where RCU is not watching, see klp_synchronize_transition().
@@ -117,6 +121,7 @@ static void notrace klp_ftrace_handler(unsigned long ip,

unlock:
preempt_enable_notrace();
+ ftrace_test_recursion_unlock(bit);
}

/*
--
2.28.0

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