linux-kernel - [PATCH] selftests/fpu: fix debugfs_simple

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Date:   Sun, 25 Oct 2020 11:20:04 +0100 (CET)
From:   Julia Lawall <julia.lawall@...ia.fr>
To:     Petteri Aimonen <jpa@....mail.kapsi.fi>,
        Borislav Petkov <bp@...e.de>,
        Nick Desaulniers <ndesaulniers@...gle.com>
cc:     nicstange@...il.com, kbuild-all@...ts.01.org,
        linux-kernel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] selftests/fpu: fix debugfs_simple_attr.cocci warnings

From: kernel test robot <lkp@...el.com>

lib/test_fpu.c:66:0-23: WARNING: test_fpu_fops should be defined with DEFINE_DEBUGFS_ATTRIBUTE

 Use DEFINE_DEBUGFS_ATTRIBUTE rather than DEFINE_SIMPLE_ATTRIBUTE
 for debugfs files.

Semantic patch information:
 Rationale: DEFINE_SIMPLE_ATTRIBUTE + debugfs_create_file()
 imposes some significant overhead as compared to
 DEFINE_DEBUGFS_ATTRIBUTE + debugfs_create_file_unsafe().

Generated by: scripts/coccinelle/api/debugfs/debugfs_simple_attr.cocci

Fixes: 4185b3b92792 ("selftests/fpu: Add an FPU selftest")
CC: Petteri Aimonen <jpa@....mail.kapsi.fi>
Signed-off-by: kernel test robot <lkp@...el.com>
Signed-off-by: Julia Lawall <julia.lawall@...ia.fr>
---

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
head:   b6f96e75ae121ead54da3f58c545d68184079f90
commit: 4185b3b92792eaec5869266e594338343421ffb0 selftests/fpu: Add an FPU selftest
:::::: branch date: 2 hours ago
:::::: commit date: 4 months ago

I don't know much about this issue, but I'm passing the warning along.
The original commit of the semantic patch contains some more information:

    In order to protect against file removal races, debugfs files created via
    debugfs_create_file() now get wrapped by a struct file_operations at their
    opening.

    If the original struct file_operations are known to be safe against removal
    races by themselves already, the proxy creation may be bypassed by creating
    the files through debugfs_create_file_unsafe().

    In order to help debugfs users who use the common
      DEFINE_SIMPLE_ATTRIBUTE() + debugfs_create_file()
    idiom to transition to removal safe struct file_operations, the helper
    macro DEFINE_DEBUGFS_ATTRIBUTE() has been introduced.

    Thus, the preferred strategy is to use
      DEFINE_DEBUGFS_ATTRIBUTE() + debugfs_create_file_unsafe()
    now.

 test_fpu.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

--- a/lib/test_fpu.c
+++ b/lib/test_fpu.c
@@ -63,7 +63,7 @@ static int test_fpu_get(void *data, u64
 	return status;
 }

-DEFINE_SIMPLE_ATTRIBUTE(test_fpu_fops, test_fpu_get, NULL, "%lld\n");
+DEFINE_DEBUGFS_ATTRIBUTE(test_fpu_fops, test_fpu_get, NULL, "%lld\n");
 static struct dentry *selftest_dir;

 static int __init test_fpu_init(void)
@@ -72,8 +72,8 @@ static int __init test_fpu_init(void)
 	if (!selftest_dir)
 		return -ENOMEM;

-	debugfs_create_file("test_fpu", 0444, selftest_dir, NULL,
-			    &test_fpu_fops);
+	debugfs_create_file_unsafe("test_fpu", 0444, selftest_dir, NULL,
+				   &test_fpu_fops);

 	return 0;
 }