[PATCH 2/2] kernel: add sysctl kernel.nr_taints

[Konstantin Khlebnikov <khlebnikov@yandex-team.ru>]

Once taint flag is set it's never cleared. Following taint could be detected
only via parsing kernel log messages which are different for each occasion.
For repeatable taints like TAINT_MACHINE_CHECK, TAINT_BAD_PAGE, TAINT_DIE,
TAINT_WARN, TAINT_LOCKUP it would be good to know count to see their rate.

This patch adds sysctl with vector of counters. One for each taint flag.
Counters are non-atomic in favor of simplicity. Exact count doesn't matter.
Writing vector of zeroes resets counters.

This is useful for detecting frequent problems with automatic monitoring.

Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
---
 include/linux/kernel.h |    1 +
 kernel/panic.c         |    2 ++
 kernel/sysctl.c        |    9 +++++++++
 3 files changed, 12 insertions(+)

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index e8a6808e4f2f..900d02167bbd 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -604,6 +604,7 @@ struct taint_flag {
 };
 
 extern const struct taint_flag taint_flags[TAINT_FLAGS_COUNT];
+extern int sysctl_nr_taints[TAINT_FLAGS_COUNT];
 
 extern const char hex_asc[];
 #define hex_asc_lo(x)	hex_asc[((x) & 0x0f)]
diff --git a/kernel/panic.c b/kernel/panic.c
index d7750a45ca8d..a3df00ebcba2 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -39,6 +39,7 @@
 int panic_on_oops = CONFIG_PANIC_ON_OOPS_VALUE;
 static unsigned long tainted_mask =
 	IS_ENABLED(CONFIG_GCC_PLUGIN_RANDSTRUCT) ? (1 << TAINT_RANDSTRUCT) : 0;
+int sysctl_nr_taints[TAINT_FLAGS_COUNT];
 static int pause_on_oops;
 static int pause_on_oops_flag;
 static DEFINE_SPINLOCK(pause_on_oops_lock);
@@ -434,6 +435,7 @@ void add_taint(unsigned flag, enum lockdep_ok lockdep_ok)
 		pr_warn("Disabling lock debugging due to kernel taint\n");
 
 	set_bit(flag, &tainted_mask);
+	sysctl_nr_taints[flag]++;
 }
 EXPORT_SYMBOL(add_taint);
 
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index b6f2f35d0bcf..5d9727556cef 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -553,6 +553,15 @@ static struct ctl_table kern_table[] = {
 		.mode		= 0644,
 		.proc_handler	= proc_taint,
 	},
+	{
+		.procname	= "nr_taints",
+		.data		= &sysctl_nr_taints,
+		.maxlen		= sizeof(sysctl_nr_taints),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec_minmax,
+		.extra1		= SYSCTL_ZERO,
+		.extra2		= SYSCTL_ZERO,
+	},
 	{
 		.procname	= "sysctl_writes_strict",
 		.data		= &sysctl_writes_strict,