linux-kernel - [RFC PATCH] checkpatch: Check check for places where dev_err_probe() would likely be better than dev

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Date:   Sun, 11 Sep 2022 15:15:33 +0200
From:   Christophe JAILLET <christophe.jaillet@...adoo.fr>
To:     Andy Whitcroft <apw@...onical.com>, Joe Perches <joe@...ches.com>,
        Dwaipayan Ray <dwaipayanray1@...il.com>,
        Lukas Bulwahn <lukas.bulwahn@...il.com>
Cc:     linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org,
        Christophe JAILLET <christophe.jaillet@...adoo.fr>
Subject: [RFC PATCH] checkpatch: Check check for places where dev_err_probe() would likely be better than dev_err()

Some functions are known to potentially return -EPROBE_DEFER. In such a
case, it is likely that dev_err_probe() is a better choice than err_err().

dev_err_probe():
  - is usually less verbose
  - generates smaller .o files
  - handles -EPROBE_DEFER so that logs are not spammed
  - automatically log the error code in a human readable way

Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
---
This patch is only a PoC to see if there is some interest in such a new
check.
The hard coded '5 lines of context' has been chosen because a typical
pattern is:

	clk = devm_clk_get(dev, "clk_lcd");
	if (IS_ERR(clk) {
		dev_err(dev, "Error meesage\n");
		return PTR_ERR(clk);
	}
---
 scripts/checkpatch.pl | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 2737e4ced574..88365749ed2e 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -2625,6 +2625,9 @@ sub process {
 	my $last_blank_line = 0;
 	my $last_coalesced_string_linenr = -1;
 
+	my $last_function_that_return_defer = "";
+	my $last_function_that_return_defer_linenr = 0;
+
 	our @report = ();
 	our $cnt_lines = 0;
 	our $cnt_error = 0;
@@ -7459,6 +7462,17 @@ sub process {
 			WARN("DUPLICATED_SYSCTL_CONST",
 				"duplicated sysctl range checking value '$1', consider using the shared one in include/linux/sysctl.h\n" . $herecurr);
 		}
+
+# check for places where dev_err_probe() would likely be better than dev_err()
+		if ($line =~ /((?:devm_)?clk_get)s*\(/) {
+			$last_function_that_return_defer = $1;
+			$last_function_that_return_defer_linenr = $linenr;
+		}
+		if ($last_function_that_return_defer_linenr >= ($linenr - 5) &&
+		    $line =~ /dev_err[^_]/) {
+			WARN("LIKELY_DEV_ERR_PROBE",
+				"dev_err_probe() is likely a better choice than err_err() after a " . $last_function_that_return_defer . "() call\n" . $herecurr);
+		}
 	}
 
 	# If we have no input at all, then there is nothing to report on
-- 
2.34.1