checkpatch: fix false positives in REPEATED_WORD warning

Presence of hexadecimal address or symbol results in false warning
message by checkpatch.pl.

For example, running checkpatch on commit b8ad540d ("mptcp: fix
memory leak in mptcp_subflow_create_socket()") results in warning:

  WARNING:REPEATED_WORD: Possible repeated word: 'ff'
      00 00 00 00 00 00 00 00 00 2f 30 0a 81 88 ff ff  ........./0.....

Similarly, the presence of list command output in commit results in
an unnecessary warning.

For example, running checkpatch on commit 899e5ffb ("perf record:
Introduce --switch-output-event") gives:

  WARNING:REPEATED_WORD: Possible repeated word: 'root'
    dr-xr-x---. 12 root root    4096 Apr 27 17:46 ..

Here, it reports 'ff' and 'root' to be repeated, but it is in fact part
of some address or code, where it has to be repeated.

In these cases, the intent of the warning to find stylistic issues in
commit messages is not met and the warning is just completely wrong in
this case.

To avoid these warnings, add an additional regex check for the directory
permission pattern and avoid checking the line for this class of
warning.  Similarly, to avoid hex pattern, check if the word consists of
hex symbols and skip this warning if it is not among the common english
words formed using hex letters.

A quick evaluation on v5.6..v5.8 showed that this fix reduces
REPEATED_WORD warnings by the frequency of 1890.

A quick manual check found all cases are related to hex output or list
command outputs in commit messages.

Link: https://lkml.kernel.org/r/20201024102253.13614-1-yashsri421@gmail.comSigned-off-by: Aditya Srivastava <yashsri421@gmail.com>
Acked-by: Joe Perches <joe@perches.com>
Cc: Dwaipayan Ray <dwaipayanray1@gmail.com>
Cc: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

scripts/checkpatch.pl

@@ -853,6 +853,13 @@ our $declaration_macros = qr{(?x:
 	(?:SKCIPHER_REQUEST|SHASH_DESC|AHASH_REQUEST)_ON_STACK\s*\(
 )};
 
+our %allow_repeated_words = (
+	add => '',
+	added => '',
+	bad => '',
+	be => '',
+);
+
 sub deparenthesize {
 	my ($string) = @_;
 	return "" if (!defined($string));
@@ -3049,7 +3056,9 @@ sub process {
 		}
 
 # check for repeated words separated by a single space
-		if ($rawline =~ /^\+/ || $in_commit_log) {
+# avoid false positive from list command eg, '-rw-r--r-- 1 root root'
+		if (($rawline =~ /^\+/ || $in_commit_log) &&
+		    $rawline !~ /[bcCdDlMnpPs\?-][rwxsStT-]{9}/) {
 			pos($rawline) = 1 if (!$in_commit_log);
 			while ($rawline =~ /\b($word_pattern) (?=($word_pattern))/g) {
 
@@ -3074,6 +3083,11 @@ sub process {
 				next if ($start_char =~ /^\S$/);
 				next if (index(" \t.,;?!", $end_char) == -1);
 
+                                # avoid repeating hex occurrences like 'ff ff fe 09 ...'
+                                if ($first =~ /\b[0-9a-f]{2,}\b/i) {
+                                        next if (!exists($allow_repeated_words{lc($first)}));
+                                }
+
 				if (WARN("REPEATED_WORD",
 					 "Possible repeated word: '$first'\n" . $herecurr) &&
 				    $fix) {