linux-kernel - [PATCH 1/2] devtmpfs: fix placement of complete() call

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Message-Id: <20210312103027.2701413-1-linux@rasmusvillemoes.dk>
Date:   Fri, 12 Mar 2021 11:30:26 +0100
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Christoph Hellwig <hch@....de>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        linux-kernel@...r.kernel.org
Subject: [PATCH 1/2] devtmpfs: fix placement of complete() call

Calling complete() from within the __init function is wrong -
theoretically, the init process could proceed all the way to freeing
the init mem before the devtmpfsd thread gets to execute the return
instruction in devtmpfs_setup().

In practice, it seems to be harmless as gcc inlines devtmpfs_setup()
into devtmpfsd(). So the calls of the __init functions init_chdir()
etc. actually happen from devtmpfs_setup(), but the __ref on that one
silences modpost (it's all right, because those calls happen before
the complete()). But it does make the __init annotation of the setup
function moot, which we'll fix in a subsequent patch.

Fixes: bcbacc4909f1 ("devtmpfs: refactor devtmpfsd()")
Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
---
 drivers/base/devtmpfs.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/base/devtmpfs.c b/drivers/base/devtmpfs.c
index 653c8c6ac7a7..aedeb2dc1a18 100644
--- a/drivers/base/devtmpfs.c
+++ b/drivers/base/devtmpfs.c
@@ -419,7 +419,6 @@ static int __init devtmpfs_setup(void *p)
 	init_chroot(".");
 out:
 	*(int *)p = err;
-	complete(&setup_done);
 	return err;
 }

@@ -432,6 +431,7 @@ static int __ref devtmpfsd(void *p)
 {
 	int err = devtmpfs_setup(p);

+	complete(&setup_done);
 	if (err)
 		return err;
 	devtmpfs_work_loop();
-- 
2.29.2