[PATCH v2 3/3] kernel: add sysctl kernel.nr_taints

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

Raised taint flag is 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:
# tr 1-9 0 < /proc/sys/kernel/nr_taints > /proc/sys/kernel/nr_taints

This is useful for detecting frequent problems with automatic monitoring.
Also tests could use this for separating expected and unexpected taints.

Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Link: https://lore.kernel.org/lkml/157503370887.8187.1663761929323284758.stgit@buzz/ (v1)
---
 Documentation/admin-guide/sysctl/kernel.rst   |   10 ++++++++++
 Documentation/admin-guide/tainted-kernels.rst |   10 ++++++++++
 include/linux/kernel.h                        |    1 +
 kernel/panic.c                                |    5 +++++
 kernel/sysctl.c                               |    9 +++++++++
 5 files changed, 35 insertions(+)

diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst
index 8456c8ed0ca5..6250575bec9f 100644
--- a/Documentation/admin-guide/sysctl/kernel.rst
+++ b/Documentation/admin-guide/sysctl/kernel.rst
@@ -56,6 +56,7 @@ show up in /proc/sys/kernel:
 - msgmnb
 - msgmni
 - nmi_watchdog
+- nr_taints                   ==> Documentation/admin-guide/tainted-kernels.rst
 - osrelease
 - ostype
 - overflowgid
@@ -495,6 +496,15 @@ in a KVM virtual machine. This default can be overridden by adding::
 to the guest kernel command line (see Documentation/admin-guide/kernel-parameters.rst).
 
 
+nr_taints:
+==========
+
+This shows vector of counters for taint flags.
+Writing vector of zeroes resets counters.
+
+See Documentation/admin-guide/tainted-kernels.rst for more information.
+
+
 numa_balancing:
 ===============
 
diff --git a/Documentation/admin-guide/tainted-kernels.rst b/Documentation/admin-guide/tainted-kernels.rst
index 13249240283c..2c5181d5e8ae 100644
--- a/Documentation/admin-guide/tainted-kernels.rst
+++ b/Documentation/admin-guide/tainted-kernels.rst
@@ -166,3 +166,13 @@ More detailed explanation for tainting
      produce extremely unusual kernel structure layouts (even performance
      pathological ones), which is important to know when debugging. Set at
      build time.
+
+
+Taint flag counters
+-------------------
+
+For detecting repeatedly set taint flags kernel counts them in sysctl:
+``cat /proc/sys/kernel/nr_taints``
+
+Writing vector of zeros resets counters but not taint flags itself:
+``tr 1-9 0 < /proc/sys/kernel/nr_taints > /proc/sys/kernel/nr_taints``
diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 3554456b2d40..2e2c4d008ac1 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -597,6 +597,7 @@ 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 a0ea0c6992b9..2e86387bbea0 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 +435,10 @@ 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);
+
+	/* proc_taint() could set unknown taint flag */
+	if (flag < ARRAY_SIZE(sysctl_nr_taints))
+		sysctl_nr_taints[flag]++;
 }
 EXPORT_SYMBOL(add_taint);
 
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 70665934d53e..21911a79305b 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,