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Date: Tue, 04 Jun 2024 10:41:17 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: linux-kernel@...r.kernel.org
Cc: Masami Hiramatsu <mhiramat@...nel.org>,
Mark Rutland <mark.rutland@....com>,
Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Alexei Starovoitov <alexei.starovoitov@...il.com>,
Florent Revest <revest@...omium.org>,
Martin KaFai Lau <martin.lau@...ux.dev>,
bpf <bpf@...r.kernel.org>,
Sven Schnelle <svens@...ux.ibm.com>,
Alexei Starovoitov <ast@...nel.org>,
Jiri Olsa <jolsa@...nel.org>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Alan Maguire <alan.maguire@...cle.com>,
Peter Zijlstra <peterz@...radead.org>,
Thomas Gleixner <tglx@...utronix.de>,
Guo Ren <guoren@...nel.org>
Subject: [for-next][PATCH 14/27] function_graph: Use a simple LRU for fgraph_array index number
From: "Masami Hiramatsu (Google)" <mhiramat@...nel.org>
Since the fgraph_array index is used for the bitmap on the shadow
stack, it may leave some entries after a function_graph instance is
removed. Thus if another instance reuses the fgraph_array index soon
after releasing it, the fgraph may confuse to call the newer callback
for the entries which are pushed by the older instance.
To avoid reusing the fgraph_array index soon after releasing, introduce
a simple LRU table for managing the index number. This will reduce the
possibility of this confusion.
Link: https://lore.kernel.org/linux-trace-kernel/171509103267.162236.6885097397289135378.stgit@devnote2
Link: https://lore.kernel.org/linux-trace-kernel/20240603190823.147421545@goodmis.org
Cc: Mark Rutland <mark.rutland@....com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc: Florent Revest <revest@...omium.org>
Cc: Martin KaFai Lau <martin.lau@...ux.dev>
Cc: bpf <bpf@...r.kernel.org>
Cc: Sven Schnelle <svens@...ux.ibm.com>
Cc: Alexei Starovoitov <ast@...nel.org>
Cc: Jiri Olsa <jolsa@...nel.org>
Cc: Arnaldo Carvalho de Melo <acme@...nel.org>
Cc: Daniel Borkmann <daniel@...earbox.net>
Cc: Alan Maguire <alan.maguire@...cle.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Guo Ren <guoren@...nel.org>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
---
kernel/trace/fgraph.c | 71 ++++++++++++++++++++++++++++++-------------
1 file changed, 50 insertions(+), 21 deletions(-)
diff --git a/kernel/trace/fgraph.c b/kernel/trace/fgraph.c
index 30bed20c655f..7fd9b03bd170 100644
--- a/kernel/trace/fgraph.c
+++ b/kernel/trace/fgraph.c
@@ -124,10 +124,48 @@ enum {
DEFINE_STATIC_KEY_FALSE(kill_ftrace_graph);
int ftrace_graph_active;
-static int fgraph_array_cnt;
-
static struct fgraph_ops *fgraph_array[FGRAPH_ARRAY_SIZE];
+/* LRU index table for fgraph_array */
+static int fgraph_lru_table[FGRAPH_ARRAY_SIZE];
+static int fgraph_lru_next;
+static int fgraph_lru_last;
+
+/* Initialize fgraph_lru_table with unused index */
+static void fgraph_lru_init(void)
+{
+ int i;
+
+ for (i = 0; i < FGRAPH_ARRAY_SIZE; i++)
+ fgraph_lru_table[i] = i;
+}
+
+/* Release the used index to the LRU table */
+static int fgraph_lru_release_index(int idx)
+{
+ if (idx < 0 || idx >= FGRAPH_ARRAY_SIZE ||
+ WARN_ON_ONCE(fgraph_lru_table[fgraph_lru_last] != -1))
+ return -1;
+
+ fgraph_lru_table[fgraph_lru_last] = idx;
+ fgraph_lru_last = (fgraph_lru_last + 1) % FGRAPH_ARRAY_SIZE;
+ return 0;
+}
+
+/* Allocate a new index from LRU table */
+static int fgraph_lru_alloc_index(void)
+{
+ int idx = fgraph_lru_table[fgraph_lru_next];
+
+ /* No id is available */
+ if (idx == -1)
+ return -1;
+
+ fgraph_lru_table[fgraph_lru_next] = -1;
+ fgraph_lru_next = (fgraph_lru_next + 1) % FGRAPH_ARRAY_SIZE;
+ return idx;
+}
+
/* Get the FRAME_OFFSET from the word from the @offset on ret_stack */
static inline int get_frame_offset(struct task_struct *t, int offset)
{
@@ -374,7 +412,7 @@ int function_graph_enter(unsigned long ret, unsigned long func,
if (offset < 0)
goto out;
- for (i = 0; i < fgraph_array_cnt; i++) {
+ for (i = 0; i < FGRAPH_ARRAY_SIZE; i++) {
struct fgraph_ops *gops = fgraph_array[i];
if (gops == &fgraph_stub)
@@ -925,7 +963,7 @@ int register_ftrace_graph(struct fgraph_ops *gops)
{
int command = 0;
int ret = 0;
- int i;
+ int i = -1;
mutex_lock(&ftrace_lock);
@@ -933,21 +971,16 @@ int register_ftrace_graph(struct fgraph_ops *gops)
/* The array must always have real data on it */
for (i = 0; i < FGRAPH_ARRAY_SIZE; i++)
fgraph_array[i] = &fgraph_stub;
+ fgraph_lru_init();
}
- /* Look for an available spot */
- for (i = 0; i < FGRAPH_ARRAY_SIZE; i++) {
- if (fgraph_array[i] == &fgraph_stub)
- break;
- }
- if (i >= FGRAPH_ARRAY_SIZE) {
+ i = fgraph_lru_alloc_index();
+ if (i < 0 || WARN_ON_ONCE(fgraph_array[i] != &fgraph_stub)) {
ret = -ENOSPC;
goto out;
}
fgraph_array[i] = gops;
- if (i + 1 > fgraph_array_cnt)
- fgraph_array_cnt = i + 1;
gops->idx = i;
ftrace_graph_active++;
@@ -975,6 +1008,7 @@ int register_ftrace_graph(struct fgraph_ops *gops)
fgraph_array[i] = &fgraph_stub;
ftrace_graph_active--;
gops->saved_func = NULL;
+ fgraph_lru_release_index(i);
}
out:
mutex_unlock(&ftrace_lock);
@@ -984,25 +1018,20 @@ int register_ftrace_graph(struct fgraph_ops *gops)
void unregister_ftrace_graph(struct fgraph_ops *gops)
{
int command = 0;
- int i;
mutex_lock(&ftrace_lock);
if (unlikely(!ftrace_graph_active))
goto out;
- if (unlikely(gops->idx < 0 || gops->idx >= fgraph_array_cnt))
+ if (unlikely(gops->idx < 0 || gops->idx >= FGRAPH_ARRAY_SIZE ||
+ fgraph_array[gops->idx] != gops))
goto out;
- WARN_ON_ONCE(fgraph_array[gops->idx] != gops);
+ if (fgraph_lru_release_index(gops->idx) < 0)
+ goto out;
fgraph_array[gops->idx] = &fgraph_stub;
- if (gops->idx + 1 == fgraph_array_cnt) {
- i = gops->idx;
- while (i >= 0 && fgraph_array[i] == &fgraph_stub)
- i--;
- fgraph_array_cnt = i + 1;
- }
ftrace_graph_active--;
--
2.43.0
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