linux-kernel - [PATCH v2 1/4] mm: Create a new system state and fix core_kernel

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Date:   Tue, 28 Sep 2021 09:15:34 +0200
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Andrew Morton <akpm@...ux-foundation.org>, arnd@...db.de
Cc:     Christophe Leroy <christophe.leroy@...roup.eu>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-s390@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-arch@...r.kernel.org,
        Gerald Schaefer <gerald.schaefer@...ux.ibm.com>
Subject: [PATCH v2 1/4] mm: Create a new system state and fix core_kernel_text()

core_kernel_text() considers that until system_state in at least
SYSTEM_RUNNING, init memory is valid.

But init memory is freed a few lines before setting SYSTEM_RUNNING,
so we have a small period of time when core_kernel_text() is wrong.

Create an intermediate system state called SYSTEM_FREEING_INIT that
is set before starting freeing init memory, and use it in
core_kernel_text() to report init memory invalid earlier.

Cc: Gerald Schaefer <gerald.schaefer@...ux.ibm.com>
Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
---
v2: New
---
 include/linux/kernel.h | 1 +
 init/main.c            | 2 ++
 kernel/extable.c       | 2 +-
 3 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 2776423a587e..471bc0593679 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -248,6 +248,7 @@ extern bool early_boot_irqs_disabled;
 extern enum system_states {
 	SYSTEM_BOOTING,
 	SYSTEM_SCHEDULING,
+	SYSTEM_FREEING_INITMEM,
 	SYSTEM_RUNNING,
 	SYSTEM_HALT,
 	SYSTEM_POWER_OFF,
diff --git a/init/main.c b/init/main.c
index 3f7216934441..c457d393fdd4 100644
--- a/init/main.c
+++ b/init/main.c
@@ -1505,6 +1505,8 @@ static int __ref kernel_init(void *unused)
 	kernel_init_freeable();
 	/* need to finish all async __init code before freeing the memory */
 	async_synchronize_full();
+
+	system_state = SYSTEM_FREEING_INITMEM;
 	kprobe_free_init_mem();
 	ftrace_free_init_mem();
 	kgdb_free_init_mem();
diff --git a/kernel/extable.c b/kernel/extable.c
index b0ea5eb0c3b4..290661f68e6b 100644
--- a/kernel/extable.c
+++ b/kernel/extable.c
@@ -76,7 +76,7 @@ int notrace core_kernel_text(unsigned long addr)
 	    addr < (unsigned long)_etext)
 		return 1;
 
-	if (system_state < SYSTEM_RUNNING &&
+	if (system_state < SYSTEM_FREEING_INITMEM &&
 	    init_kernel_text(addr))
 		return 1;
 	return 0;
-- 
2.31.1