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Message-Id: <20240531-fault-injection-statickeys-v1-1-a513fd0a9614@suse.cz>
Date: Fri, 31 May 2024 11:33:32 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: Akinobu Mita <akinobu.mita@...il.com>, Christoph Lameter <cl@...ux.com>,
David Rientjes <rientjes@...gle.com>, Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>,
"Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>,
Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
"David S. Miller" <davem@...emloft.net>,
Masami Hiramatsu <mhiramat@...nel.org>,
Steven Rostedt <rostedt@...dmis.org>, Mark Rutland <mark.rutland@....com>
Cc: Jiri Olsa <jolsa@...nel.org>, Roman Gushchin <roman.gushchin@...ux.dev>,
Hyeonggon Yoo <42.hyeyoo@...il.com>, linux-kernel@...r.kernel.org,
linux-mm@...ck.org, bpf@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
Vlastimil Babka <vbabka@...e.cz>
Subject: [PATCH RFC 1/4] fault-inject: add support for static keys around
fault injection sites
Some fault injection sites are placed in hotpaths and incur overhead
even if not enabled, due to one or more function calls leading up to
should_fail_ex() that returns false due to attr->probability == 0.
This overhead can be eliminated if the outermost call into the checks is
guarded with a static key, so add support for that. The framework should
be told that such static key exist for a fault_attr, by initializing
fault_attr->active with the static key address. When it's not NULL,
enable the static key from setup_fault_attr() when the fault probability
is non-zero.
Also wire up writing into debugfs "probability" file to enable or
disable the static key when transitioning between zero and non-zero
probability.
For now, do not add configfs interface support as the immediate plan is
to leverage this for should_failslab() and should_fail_alloc_page()
after other necessary preparatory changes, and none of the configfs
based fault injection users.
Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
---
include/linux/fault-inject.h | 7 ++++++-
lib/fault-inject.c | 43 ++++++++++++++++++++++++++++++++++++++++++-
2 files changed, 48 insertions(+), 2 deletions(-)
diff --git a/include/linux/fault-inject.h b/include/linux/fault-inject.h
index 6d5edef09d45..cfe75cc1bac4 100644
--- a/include/linux/fault-inject.h
+++ b/include/linux/fault-inject.h
@@ -9,6 +9,7 @@
#include <linux/configfs.h>
#include <linux/ratelimit.h>
#include <linux/atomic.h>
+#include <linux/jump_label.h>
/*
* For explanation of the elements of this struct, see
@@ -30,13 +31,14 @@ struct fault_attr {
unsigned long count;
struct ratelimit_state ratelimit_state;
struct dentry *dname;
+ struct static_key *active;
};
enum fault_flags {
FAULT_NOWARN = 1 << 0,
};
-#define FAULT_ATTR_INITIALIZER { \
+#define FAULT_ATTR_INITIALIZER_KEY(_key) { \
.interval = 1, \
.times = ATOMIC_INIT(1), \
.require_end = ULONG_MAX, \
@@ -44,8 +46,11 @@ enum fault_flags {
.ratelimit_state = RATELIMIT_STATE_INIT_DISABLED, \
.verbose = 2, \
.dname = NULL, \
+ .active = (_key), \
}
+#define FAULT_ATTR_INITIALIZER FAULT_ATTR_INITIALIZER_KEY(NULL)
+
#define DECLARE_FAULT_ATTR(name) struct fault_attr name = FAULT_ATTR_INITIALIZER
int setup_fault_attr(struct fault_attr *attr, char *str);
bool should_fail_ex(struct fault_attr *attr, ssize_t size, int flags);
diff --git a/lib/fault-inject.c b/lib/fault-inject.c
index d608f9b48c10..93c46d2ec106 100644
--- a/lib/fault-inject.c
+++ b/lib/fault-inject.c
@@ -35,6 +35,9 @@ int setup_fault_attr(struct fault_attr *attr, char *str)
atomic_set(&attr->times, times);
atomic_set(&attr->space, space);
+ if (probability != 0 && attr->active)
+ static_key_slow_inc(attr->active);
+
return 1;
}
EXPORT_SYMBOL_GPL(setup_fault_attr);
@@ -166,6 +169,12 @@ EXPORT_SYMBOL_GPL(should_fail);
#ifdef CONFIG_FAULT_INJECTION_DEBUG_FS
+/*
+ * Protect updating probability from debugfs as that may trigger static key
+ * changes when changing between zero and non-zero.
+ */
+static DEFINE_MUTEX(probability_mutex);
+
static int debugfs_ul_set(void *data, u64 val)
{
*(unsigned long *)data = val;
@@ -186,6 +195,38 @@ static void debugfs_create_ul(const char *name, umode_t mode,
debugfs_create_file(name, mode, parent, value, &fops_ul);
}
+static int debugfs_prob_set(void *data, u64 val)
+{
+ struct fault_attr *attr = data;
+
+ mutex_lock(&probability_mutex);
+
+ if (attr->active) {
+ if (attr->probability != 0 && val == 0) {
+ static_key_slow_dec(attr->active);
+ } else if (attr->probability == 0 && val != 0) {
+ static_key_slow_inc(attr->active);
+ }
+ }
+
+ attr->probability = val;
+
+ mutex_unlock(&probability_mutex);
+
+ return 0;
+}
+
+static int debugfs_prob_get(void *data, u64 *val)
+{
+ struct fault_attr *attr = data;
+
+ *val = attr->probability;
+
+ return 0;
+}
+
+DEFINE_SIMPLE_ATTRIBUTE(fops_prob, debugfs_prob_get, debugfs_prob_set, "%llu\n");
+
#ifdef CONFIG_FAULT_INJECTION_STACKTRACE_FILTER
static int debugfs_stacktrace_depth_set(void *data, u64 val)
@@ -218,7 +259,7 @@ struct dentry *fault_create_debugfs_attr(const char *name,
if (IS_ERR(dir))
return dir;
- debugfs_create_ul("probability", mode, dir, &attr->probability);
+ debugfs_create_file("probability", mode, dir, &attr, &fops_prob);
debugfs_create_ul("interval", mode, dir, &attr->interval);
debugfs_create_atomic_t("times", mode, dir, &attr->times);
debugfs_create_atomic_t("space", mode, dir, &attr->space);
--
2.45.1
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