linux-kernel - [PATCH v3 1/3] livepatch: Skip task_call

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Date:   Fri, 24 Feb 2023 08:49:59 -0800
From:   Josh Poimboeuf <jpoimboe@...nel.org>
To:     live-patching@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, Seth Forshee <sforshee@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Song Liu <song@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Petr Mladek <pmladek@...e.com>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        Miroslav Benes <mbenes@...e.cz>,
        Jiri Kosina <jikos@...nel.org>, Ingo Molnar <mingo@...hat.com>,
        Rik van Riel <riel@...riel.com>
Subject: [PATCH v3 1/3] livepatch: Skip task_call_func() for current task

The current task doesn't need the scheduler's protection to unwind its
own stack.

Tested-by: Seth Forshee (DigitalOcean) <sforshee@...nel.org>
Reviewed-by: Petr Mladek <pmladek@...e.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>
---
 kernel/livepatch/transition.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c
index f1b25ec581e0..4d1f443778f7 100644
--- a/kernel/livepatch/transition.c
+++ b/kernel/livepatch/transition.c
@@ -307,7 +307,11 @@ static bool klp_try_switch_task(struct task_struct *task)
 	 * functions.  If all goes well, switch the task to the target patch
 	 * state.
 	 */
-	ret = task_call_func(task, klp_check_and_switch_task, &old_name);
+	if (task == current)
+		ret = klp_check_and_switch_task(current, &old_name);
+	else
+		ret = task_call_func(task, klp_check_and_switch_task, &old_name);
+
 	switch (ret) {
 	case 0:		/* success */
 		break;
-- 
2.39.1