linux-kernel - [PATCH v2] ext4: Enable code path when DX

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Message-Id: <20210201003125.90257-1-viniciustinti@gmail.com>
Date:   Mon,  1 Feb 2021 00:31:25 +0000
From:   Vinicius Tinti <viniciustinti@...il.com>
To:     Andreas Dilger <adilger.kernel@...ger.ca>,
        Nathan Chancellor <natechancellor@...il.com>
Cc:     Theodore Ts'o <tytso@....edu>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Vinicius Tinti <viniciustinti@...il.com>,
        linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org,
        clang-built-linux@...glegroups.com
Subject: [PATCH v2] ext4: Enable code path when DX_DEBUG is set

By enabling -Wunreachable-code-aggressive on Clang the following code
paths are unreachable.

This has been present since commit ac27a0ec112a ("[PATCH] ext4: initial
copy of files from ext3") and fs/ext3 had it present at the beginning of
git history. It has not been changed since.

Clang warns:

fs/ext4/namei.c:831:17: warning: code will never be executed
[-Wunreachable-code]
                        unsigned n = count - 1;
                                     ^~~~~
fs/ext4/namei.c:830:7: note: silence by adding parentheses to mark code as
explicitly dead
                if (0) { // linear search cross check
                    ^
                    /* DISABLES CODE */ ( )

Signed-off-by: Vinicius Tinti <viniciustinti@...il.com>
---
 fs/ext4/namei.c | 23 ++++++++++++-----------
 1 file changed, 12 insertions(+), 11 deletions(-)

diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index cf652ba3e74d..46ae6a4e4be5 100644
--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -827,20 +827,21 @@ dx_probe(struct ext4_filename *fname, struct inode *dir,
 				p = m + 1;
 		}
 
-		if (0) { // linear search cross check
-			unsigned n = count - 1;
-			at = entries;
-			while (n--)
+#ifdef DX_DEBUG
+		// linear search cross check
+		unsigned n = count - 1;
+		at = entries;
+		while (n--)
+		{
+			dxtrace(printk(KERN_CONT ","));
+			if (dx_get_hash(++at) > hash)
 			{
-				dxtrace(printk(KERN_CONT ","));
-				if (dx_get_hash(++at) > hash)
-				{
-					at--;
-					break;
-				}
+				at--;
+				break;
 			}
-			ASSERT(at == p - 1);
 		}
+		ASSERT(at == p - 1);
+#endif
 
 		at = p - 1;
 		dxtrace(printk(KERN_CONT " %x->%u\n",
-- 
2.25.1