[PATCH 5.15 170/201] tracing: Place trace_pid_list logic into abstract functions

Greg Kroah-Hartman
2022-07-27T17:22:44Z

From: Steven Rostedt (VMware) <rostedt@goodmis.org>

[ Upstream commit 6954e415264eeb5ee6be0d22d789ad12c995ee64 ]

Instead of having the logic that does trace_pid_list open coded, wrap it in
abstract functions. This will allow a rewrite of the logic that implements
the trace_pid_list without affecting the users.

Note, this causes a change in behavior. Every time a pid is written into
the set_*_pid file, it creates a new list and uses RCU to update it. If
pid_max is lowered, but there was a pid currently in the list that was
higher than pid_max, those pids will now be removed on updating the list.
The old behavior kept that from happening.

The rewrite of the pid_list logic will no longer depend on pid_max,
and will return the old behavior.

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
kernel/trace/Makefile | 1 +
kernel/trace/ftrace.c | 6 +-
kernel/trace/pid_list.c | 160 ++++++++++++++++++++++++++++++++++++
kernel/trace/pid_list.h | 13 +++
kernel/trace/trace.c | 78 ++++++------------
kernel/trace/trace.h | 14 +++-
kernel/trace/trace_events.c | 6 +-
7 files changed, 217 insertions(+), 61 deletions(-)
create mode 100644 kernel/trace/pid_list.c
create mode 100644 kernel/trace/pid_list.h

diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile
index 6de5d4d63165..bedc5caceec7 100644
--- a/kernel/trace/Makefile
+++ b/kernel/trace/Makefile
@@ -47,6 +47,7 @@ obj-$(CONFIG_TRACING) += trace_output.o
obj-$(CONFIG_TRACING) += trace_seq.o
obj-$(CONFIG_TRACING) += trace_stat.o
obj-$(CONFIG_TRACING) += trace_printk.o
+obj-$(CONFIG_TRACING) += pid_list.o
obj-$(CONFIG_TRACING_MAP) += tracing_map.o
obj-$(CONFIG_PREEMPTIRQ_DELAY_TEST) += preemptirq_delay_test.o
obj-$(CONFIG_SYNTH_EVENT_GEN_TEST) += synth_event_gen_test.o
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 53a1af21d25c..e215a9c96971 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -7184,10 +7184,10 @@ static void clear_ftrace_pids(struct trace_array *tr, int type)
synchronize_rcu();

if ((type & TRACE_PIDS) && pid_list)
- trace_free_pid_list(pid_list);
+ trace_pid_list_free(pid_list);

if ((type & TRACE_NO_PIDS) && no_pid_list)
- trace_free_pid_list(no_pid_list);
+ trace_pid_list_free(no_pid_list);
}

void ftrace_clear_pids(struct trace_array *tr)
@@ -7428,7 +7428,7 @@ pid_write(struct file *filp, const char __user *ubuf,

if (filtered_pids) {
synchronize_rcu();
- trace_free_pid_list(filtered_pids);
+ trace_pid_list_free(filtered_pids);
} else if (pid_list && !other_pids) {
/* Register a probe to set whether to ignore the tracing of a task */
register_trace_sched_switch(ftrace_filter_pid_sched_switch_probe, tr);
diff --git a/kernel/trace/pid_list.c b/kernel/trace/pid_list.c
new file mode 100644
index 000000000000..4483ef70b562
--- /dev/null
+++ b/kernel/trace/pid_list.c
@@ -0,0 +1,160 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2021 VMware Inc, Steven Rostedt <rostedt@goodmis.org>
+ */
+#include <linux/vmalloc.h>
+#include <linux/slab.h>
+#include "trace.h"
+
+/**
+ * trace_pid_list_is_set - test if the pid is set in the list
+ * @pid_list: The pid list to test
+ * @pid: The pid to to see if set in the list.
+ *
+ * Tests if @pid is is set in the @pid_list. This is usually called
+ * from the scheduler when a task is scheduled. Its pid is checked
+ * if it should be traced or not.
+ *
+ * Return true if the pid is in the list, false otherwise.
+ */
+bool trace_pid_list_is_set(struct trace_pid_list *pid_list, unsigned int pid)
+{
+ /*
+ * If pid_max changed after filtered_pids was created, we
+ * by default ignore all pids greater than the previous pid_max.
+ */
+ if (pid >= pid_list->pid_max)
+ return false;
+
+ return test_bit(pid, pid_list->pids);
+}
+
+/**
+ * trace_pid_list_set - add a pid to the list
+ * @pid_list: The pid list to add the @pid to.
+ * @pid: The pid to add.
+ *
+ * Adds @pid to @pid_list. This is usually done explicitly by a user
+ * adding a task to be traced, or indirectly by the fork function
+ * when children should be traced and a task's pid is in the list.
+ *
+ * Return 0 on success, negative otherwise.
+ */
+int trace_pid_list_set(struct trace_pid_list *pid_list, unsigned int pid)
+{
+ /* Sorry, but we don't support pid_max changing after setting */
+ if (pid >= pid_list->pid_max)
+ return -EINVAL;
+
+ set_bit(pid, pid_list->pids);
+
+ return 0;
+}
+
+/**
+ * trace_pid_list_clear - remove a pid from the list
+ * @pid_list: The pid list to remove the @pid from.
+ * @pid: The pid to remove.
+ *
+ * Removes @pid from @pid_list. This is usually done explicitly by a user
+ * removing tasks from tracing, or indirectly by the exit function
+ * when a task that is set to be traced exits.
+ *
+ * Return 0 on success, negative otherwise.
+ */
+int trace_pid_list_clear(struct trace_pid_list *pid_list, unsigned int pid)
+{
+ /* Sorry, but we don't support pid_max changing after setting */
+ if (pid >= pid_list->pid_max)
+ return -EINVAL;
+
+ clear_bit(pid, pid_list->pids);
+
+ return 0;
+}
+
+/**
+ * trace_pid_list_next - return the next pid in the list
+ * @pid_list: The pid list to examine.
+ * @pid: The pid to start from
+ * @next: The pointer to place the pid that is set starting from @pid.
+ *
+ * Looks for the next consecutive pid that is in @pid_list starting
+ * at the pid specified by @pid. If one is set (including @pid), then
+ * that pid is placed into @next.
+ *
+ * Return 0 when a pid is found, -1 if there are no more pids included.
+ */
+int trace_pid_list_next(struct trace_pid_list *pid_list, unsigned int pid,
+ unsigned int *next)
+{
+ pid = find_next_bit(pid_list->pids, pid_list->pid_max, pid);
+
+ if (pid < pid_list->pid_max) {
+ *next = pid;
+ return 0;
+ }
+ return -1;
+}
+
+/**
+ * trace_pid_list_first - return the first pid in the list
+ * @pid_list: The pid list to examine.
+ * @pid: The pointer to place the pid first found pid that is set.
+ *
+ * Looks for the first pid that is set in @pid_list, and places it
+ * into @pid if found.
+ *
+ * Return 0 when a pid is found, -1 if there are no pids set.
+ */
+int trace_pid_list_first(struct trace_pid_list *pid_list, unsigned int *pid)
+{
+ unsigned int first;
+
+ first = find_first_bit(pid_list->pids, pid_list->pid_max);
+
+ if (first < pid_list->pid_max) {
+ *pid = first;
+ return 0;
+ }
+ return -1;
+}
+
+/**
+ * trace_pid_list_alloc - create a new pid_list
+ *
+ * Allocates a new pid_list to store pids into.
+ *
+ * Returns the pid_list on success, NULL otherwise.
+ */
+struct trace_pid_list *trace_pid_list_alloc(void)
+{
+ struct trace_pid_list *pid_list;
+
+ pid_list = kmalloc(sizeof(*pid_list), GFP_KERNEL);
+ if (!pid_list)
+ return NULL;
+
+ pid_list->pid_max = READ_ONCE(pid_max);
+
+ pid_list->pids = vzalloc((pid_list->pid_max + 7) >> 3);
+ if (!pid_list->pids) {
+ kfree(pid_list);
+ return NULL;
+ }
+ return pid_list;
+}
+
+/**
+ * trace_pid_list_free - Frees an allocated pid_list.
+ *
+ * Frees the memory for a pid_list that was allocated.
+ */
+void trace_pid_list_free(struct trace_pid_list *pid_list)
+{
+ if (!pid_list)
+ return;
+
+ vfree(pid_list->pids);
+ kfree(pid_list);
+}
diff --git a/kernel/trace/pid_list.h b/kernel/trace/pid_list.h
new file mode 100644
index 000000000000..80d0ecfe1536
--- /dev/null
+++ b/kernel/trace/pid_list.h
@@ -0,0 +1,13 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/* Do not include this file directly. */
+
+#ifndef _TRACE_INTERNAL_PID_LIST_H
+#define _TRACE_INTERNAL_PID_LIST_H
+
+struct trace_pid_list {
+ int pid_max;
+ unsigned long *pids;
+};
+
+#endif /* _TRACE_INTERNAL_PID_LIST_H */
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index f752f2574630..abbe8489faae 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -516,12 +516,6 @@ int call_filter_check_discard(struct trace_event_call *call, void *rec,
return 0;
}

-void trace_free_pid_list(struct trace_pid_list *pid_list)
-{
- vfree(pid_list->pids);
- kfree(pid_list);
-}
-
/**
* trace_find_filtered_pid - check if a pid exists in a filtered_pid list
* @filtered_pids: The list of pids to check
@@ -532,14 +526,7 @@ void trace_free_pid_list(struct trace_pid_list *pid_list)
bool
trace_find_filtered_pid(struct trace_pid_list *filtered_pids, pid_t search_pid)
{
- /*
- * If pid_max changed after filtered_pids was created, we
- * by default ignore all pids greater than the previous pid_max.
- */
- if (search_pid >= filtered_pids->pid_max)
- return false;
-
- return test_bit(search_pid, filtered_pids->pids);
+ return trace_pid_list_is_set(filtered_pids, search_pid);
}

/**
@@ -596,15 +583,11 @@ void trace_filter_add_remove_task(struct trace_pid_list *pid_list,
return;
}

- /* Sorry, but we don't support pid_max changing after setting */
- if (task->pid >= pid_list->pid_max)
- return;
-
/* "self" is set for forks, and NULL for exits */
if (self)
- set_bit(task->pid, pid_list->pids);
+ trace_pid_list_set(pid_list, task->pid);
else
- clear_bit(task->pid, pid_list->pids);
+ trace_pid_list_clear(pid_list, task->pid);
}

/**
@@ -621,18 +604,19 @@ void trace_filter_add_remove_task(struct trace_pid_list *pid_list,
*/
void *trace_pid_next(struct trace_pid_list *pid_list, void *v, loff_t *pos)
{
- unsigned long pid = (unsigned long)v;
+ long pid = (unsigned long)v;
+ unsigned int next;

(*pos)++;

/* pid already is +1 of the actual previous bit */
- pid = find_next_bit(pid_list->pids, pid_list->pid_max, pid);
+ if (trace_pid_list_next(pid_list, pid, &next) < 0)
+ return NULL;

- /* Return pid + 1 to allow zero to be represented */
- if (pid < pid_list->pid_max)
- return (void *)(pid + 1);
+ pid = next;

- return NULL;
+ /* Return pid + 1 to allow zero to be represented */
+ return (void *)(pid + 1);
}

/**
@@ -649,12 +633,14 @@ void *trace_pid_next(struct trace_pid_list *pid_list, void *v, loff_t *pos)
void *trace_pid_start(struct trace_pid_list *pid_list, loff_t *pos)
{
unsigned long pid;
+ unsigned int first;
loff_t l = 0;

- pid = find_first_bit(pid_list->pids, pid_list->pid_max);
- if (pid >= pid_list->pid_max)
+ if (trace_pid_list_first(pid_list, &first) < 0)
return NULL;

+ pid = first;
+
/* Return pid + 1 so that zero can be the exit value */
for (pid++; pid && l < *pos;
pid = (unsigned long)trace_pid_next(pid_list, (void *)pid, &l))
@@ -690,7 +676,7 @@ int trace_pid_write(struct trace_pid_list *filtered_pids,
unsigned long val;
int nr_pids = 0;
ssize_t read = 0;
- ssize_t ret = 0;
+ ssize_t ret;
loff_t pos;
pid_t pid;

@@ -703,34 +689,23 @@ int trace_pid_write(struct trace_pid_list *filtered_pids,
* the user. If the operation fails, then the current list is
* not modified.
*/
- pid_list = kmalloc(sizeof(*pid_list), GFP_KERNEL);
+ pid_list = trace_pid_list_alloc();
if (!pid_list) {
trace_parser_put(&parser);
return -ENOMEM;
}

- pid_list->pid_max = READ_ONCE(pid_max);
-
- /* Only truncating will shrink pid_max */
- if (filtered_pids && filtered_pids->pid_max > pid_list->pid_max)
- pid_list->pid_max = filtered_pids->pid_max;
-
- pid_list->pids = vzalloc((pid_list->pid_max + 7) >> 3);
- if (!pid_list->pids) {
- trace_parser_put(&parser);
- kfree(pid_list);
- return -ENOMEM;
- }
-
if (filtered_pids) {
/* copy the current bits to the new max */
- for_each_set_bit(pid, filtered_pids->pids,
- filtered_pids->pid_max) {
- set_bit(pid, pid_list->pids);
+ ret = trace_pid_list_first(filtered_pids, &pid);
+ while (!ret) {
+ trace_pid_list_set(pid_list, pid);
+ ret = trace_pid_list_next(filtered_pids, pid + 1, &pid);
nr_pids++;
}
}

+ ret = 0;
while (cnt > 0) {

pos = 0;
@@ -746,12 +721,13 @@ int trace_pid_write(struct trace_pid_list *filtered_pids,
ret = -EINVAL;
if (kstrtoul(parser.buffer, 0, &val))
break;
- if (val >= pid_list->pid_max)
- break;

pid = (pid_t)val;

- set_bit(pid, pid_list->pids);
+ if (trace_pid_list_set(pid_list, pid) < 0) {
+ ret = -1;
+ break;
+ }
nr_pids++;

trace_parser_clear(&parser);
@@ -760,13 +736,13 @@ int trace_pid_write(struct trace_pid_list *filtered_pids,
trace_parser_put(&parser);

if (ret < 0) {
- trace_free_pid_list(pid_list);
+ trace_pid_list_free(pid_list);
return ret;
}

if (!nr_pids) {
/* Cleared the list of pids */
- trace_free_pid_list(pid_list);
+ trace_pid_list_free(pid_list);
read = ret;
pid_list = NULL;
}
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 421374c304fc..d6763366a320 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -22,6 +22,8 @@
#include <linux/ctype.h>
#include <linux/once_lite.h>

+#include "pid_list.h"
+
#ifdef CONFIG_FTRACE_SYSCALLS
#include <asm/unistd.h> /* For NR_SYSCALLS */
#include <asm/syscall.h> /* some archs define it here */
@@ -191,10 +193,14 @@ struct trace_options {
struct trace_option_dentry *topts;
};

-struct trace_pid_list {
- int pid_max;
- unsigned long *pids;
-};
+struct trace_pid_list *trace_pid_list_alloc(void);
+void trace_pid_list_free(struct trace_pid_list *pid_list);
+bool trace_pid_list_is_set(struct trace_pid_list *pid_list, unsigned int pid);
+int trace_pid_list_set(struct trace_pid_list *pid_list, unsigned int pid);
+int trace_pid_list_clear(struct trace_pid_list *pid_list, unsigned int pid);
+int trace_pid_list_first(struct trace_pid_list *pid_list, unsigned int *pid);
+int trace_pid_list_next(struct trace_pid_list *pid_list, unsigned int pid,
+ unsigned int *next);

enum {
TRACE_PIDS = BIT(0),
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index ea3fbfa87fdd..c4f654efb77a 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -900,10 +900,10 @@ static void __ftrace_clear_event_pids(struct trace_array *tr, int type)
tracepoint_synchronize_unregister();

if ((type & TRACE_PIDS) && pid_list)
- trace_free_pid_list(pid_list);
+ trace_pid_list_free(pid_list);

if ((type & TRACE_NO_PIDS) && no_pid_list)
- trace_free_pid_list(no_pid_list);
+ trace_pid_list_free(no_pid_list);
}

static void ftrace_clear_event_pids(struct trace_array *tr, int type)
@@ -1982,7 +1982,7 @@ event_pid_write(struct file *filp, const char __user *ubuf,

if (filtered_pids) {
tracepoint_synchronize_unregister();
- trace_free_pid_list(filtered_pids);
+ trace_pid_list_free(filtered_pids);
} else if (pid_list && !other_pids) {
register_pid_events(tr);
}
--
2.35.1