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Date:   Wed,  3 Mar 2021 10:38:45 +0100
Message-Id: <20210303093845.2743309-1-elver@google.com>
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Subject: [PATCH] kcsan, debugfs: Move debugfs file creation out of early init
From:   Marco Elver <elver@google.com>
To:     gregkh@linuxfoundation.org, rafael@kernel.org
Cc:     paulmck@kernel.org, dvyukov@google.com, glider@google.com,
        andreyknvl@google.com, kasan-dev@googlegroups.com,
        linux-kernel@vger.kernel.org, Marco Elver <elver@google.com>,
        stable <stable@vger.kernel.org>
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Precedence: bulk

Commit 56348560d495 ("debugfs: do not attempt to create a new file
before the filesystem is initalized") forbids creating new debugfs files
until debugfs is fully initialized. This breaks KCSAN's debugfs file
creation, which happened at the end of __init().

There is no reason to create the debugfs file during early
initialization. Therefore, move it into a late_initcall() callback.

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: stable <stable@vger.kernel.org>
Fixes: 56348560d495 ("debugfs: do not attempt to create a new file before the filesystem is initalized")
Signed-off-by: Marco Elver <elver@google.com>
---
I've marked this for 'stable', since 56348560d495 is also intended for
stable, and would subsequently break KCSAN in all stable kernels where
KCSAN is available (since 5.8).
---
 kernel/kcsan/core.c    | 2 --
 kernel/kcsan/debugfs.c | 4 +++-
 kernel/kcsan/kcsan.h   | 5 -----
 3 files changed, 3 insertions(+), 8 deletions(-)

diff --git a/kernel/kcsan/core.c b/kernel/kcsan/core.c
index 8c3867640c21..45c821d4e8bd 100644
--- a/kernel/kcsan/core.c
+++ b/kernel/kcsan/core.c
@@ -644,8 +644,6 @@ void __init kcsan_init(void)
 
 	BUG_ON(!in_task());
 
-	kcsan_debugfs_init();
-
 	for_each_possible_cpu(cpu)
 		per_cpu(kcsan_rand_state, cpu) = (u32)get_cycles();
 
diff --git a/kernel/kcsan/debugfs.c b/kernel/kcsan/debugfs.c
index c837ce6c52e6..c1dd02f3be8b 100644
--- a/kernel/kcsan/debugfs.c
+++ b/kernel/kcsan/debugfs.c
@@ -266,7 +266,9 @@ static const struct file_operations debugfs_ops =
 	.release = single_release
 };
 
-void __init kcsan_debugfs_init(void)
+static void __init kcsan_debugfs_init(void)
 {
 	debugfs_create_file("kcsan", 0644, NULL, NULL, &debugfs_ops);
 }
+
+late_initcall(kcsan_debugfs_init);
diff --git a/kernel/kcsan/kcsan.h b/kernel/kcsan/kcsan.h
index 594a5dd4842a..9881099d4179 100644
--- a/kernel/kcsan/kcsan.h
+++ b/kernel/kcsan/kcsan.h
@@ -31,11 +31,6 @@ extern bool kcsan_enabled;
 void kcsan_save_irqtrace(struct task_struct *task);
 void kcsan_restore_irqtrace(struct task_struct *task);
 
-/*
- * Initialize debugfs file.
- */
-void kcsan_debugfs_init(void);
-
 /*
  * Statistics counters displayed via debugfs; should only be modified in
  * slow-paths.
-- 
2.30.1.766.gb4fecdf3b7-goog