checkpatch: add some <foo>_destroy functions to NEEDLESS_IF tests

Sergey Senozhatsky has modified several destroy functions that can
now be called with NULL values.

 - kmem_cache_destroy()
 - mempool_destroy()
 - dma_pool_destroy()

Update checkpatch to warn when those functions are preceded by an if.

Update checkpatch to --fix all the calls too only when the code style
form is using leading tabs.

from:
	if (foo)
		<func>(foo);
to:
	<func>(foo);
Signed-off-by: NJoe Perches <joe@perches.com>
Tested-by: NSergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Julia Lawall <julia.lawall@lip6.fr>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

scripts/checkpatch.pl

@@ -4836,10 +4836,34 @@ sub process {
 
 # check for needless "if (<foo>) fn(<foo>)" uses
 		if ($prevline =~ /\bif\s*\(\s*($Lval)\s*\)/) {
-			my $expr = '\s*\(\s*' . quotemeta($1) . '\s*\)\s*;';
-			if ($line =~ /\b(kfree|usb_free_urb|debugfs_remove(?:_recursive)?)$expr/) {
-				WARN('NEEDLESS_IF',
-				     "$1(NULL) is safe and this check is probably not required\n" . $hereprev);
+			my $tested = quotemeta($1);
+			my $expr = '\s*\(\s*' . $tested . '\s*\)\s*;';
+			if ($line =~ /\b(kfree|usb_free_urb|debugfs_remove(?:_recursive)?|(?:kmem_cache|mempool|dma_pool)_destroy)$expr/) {
+				my $func = $1;
+				if (WARN('NEEDLESS_IF',
+					 "$func(NULL) is safe and this check is probably not required\n" . $hereprev) &&
+				    $fix) {
+					my $do_fix = 1;
+					my $leading_tabs = "";
+					my $new_leading_tabs = "";
+					if ($lines[$linenr - 2] =~ /^\+(\t*)if\s*\(\s*$tested\s*\)\s*$/) {
+						$leading_tabs = $1;
+					} else {
+						$do_fix = 0;
+					}
+					if ($lines[$linenr - 1] =~ /^\+(\t+)$func\s*\(\s*$tested\s*\)\s*;\s*$/) {
+						$new_leading_tabs = $1;
+						if (length($leading_tabs) + 1 ne length($new_leading_tabs)) {
+							$do_fix = 0;
+						}
+					} else {
+						$do_fix = 0;
+					}
+					if ($do_fix) {
+						fix_delete_line($fixlinenr - 1, $prevrawline);
+						$fixed[$fixlinenr] =~ s/^\+$new_leading_tabs/\+$leading_tabs/;
+					}
+				}
 			}
 		}