linux-kernel - Re: [PATCH] livepatch: klp_send_signal should treat PF_IO_WORKER like PF

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Date:   Thu, 25 Mar 2021 10:30:36 +0100 (CET)
From:   Miroslav Benes <mbenes@...e.cz>
To:     Joe Lawrence <joe.lawrence@...hat.com>
cc:     Dong Kai <dongkai11@...wei.com>, jpoimboe@...hat.com,
        jikos@...nel.org, pmladek@...e.com, axboe@...nel.dk,
        live-patching@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] livepatch: klp_send_signal should treat PF_IO_WORKER
 like PF_KTHREAD

> (PF_KTHREAD | PF_IO_WORKER) is open coded in soo many places maybe this is a
> silly question, but...
> 
> If the livepatch code could use fake_signal_wake_up(), we could consolidate
> the pattern in klp_send_signals() with the one in freeze_task().  Then there
> would only one place for wake up / fake signal logic.
> 
> I don't fully understand the differences in the freeze_task() version, so I
> only pose this as a question and not v2 request.

The plan was to remove our live patching fake signal completely and use 
the new infrastructure Jens proposed in the past.

Something like

diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c
index f6310f848f34..3a4beb9395c4 100644
--- a/kernel/livepatch/transition.c
+++ b/kernel/livepatch/transition.c
@@ -9,6 +9,7 @@
 
 #include <linux/cpu.h>
 #include <linux/stacktrace.h>
+#include <linux/tracehook.h>
 #include "core.h"
 #include "patch.h"
 #include "transition.h"
@@ -369,9 +370,7 @@ static void klp_send_signals(void)
                         * Send fake signal to all non-kthread tasks which are
                         * still not migrated.
                         */
-                       spin_lock_irq(&task->sighand->siglock);
-                       signal_wake_up(task, 0);
-                       spin_unlock_irq(&task->sighand->siglock);
+                       set_notify_signal(task);
                }
        }
        read_unlock(&tasklist_lock);
diff --git a/kernel/signal.c b/kernel/signal.c
index a15c584a0455..b7cf4eda8611 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -181,8 +181,7 @@ void recalc_sigpending_and_wake(struct task_struct *t)
 
 void recalc_sigpending(void)
 {
-       if (!recalc_sigpending_tsk(current) && !freezing(current) &&
-           !klp_patch_pending(current))
+       if (!recalc_sigpending_tsk(current) && !freezing(current))
                clear_thread_flag(TIF_SIGPENDING);
 
 }


Let me verify it still works and there are all the needed pieces merged 
for all the architectures we support (x86_64, ppc64le and s390x). I'll 
send a proper patch then.

Miroslav