Merge tag 'trace-v5.11' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace

Pull tracing updates from Steven Rostedt:
 "The major update to this release is that there's a new arch config
  option called CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS.

  Currently, only x86_64 enables it. All the ftrace callbacks now take a
  struct ftrace_regs instead of a struct pt_regs. If the architecture
  has HAVE_DYNAMIC_FTRACE_WITH_ARGS enabled, then the ftrace_regs will
  have enough information to read the arguments of the function being
  traced, as well as access to the stack pointer.

  This way, if a user (like live kernel patching) only cares about the
  arguments, then it can avoid using the heavier weight "regs" callback,
  that puts in enough information in the struct ftrace_regs to simulate
  a breakpoint exception (needed for kprobes).

  A new config option that audits the timestamps of the ftrace ring
  buffer at most every event recorded.

  Ftrace recursion protection has been cleaned up to move the protection
  to the callback itself (this saves on an extra function call for those
  callbacks).

  Perf now handles its own RCU protection and does not depend on ftrace
  to do it for it (saving on that extra function call).

  New debug option to add "recursed_functions" file to tracefs that
  lists all the places that triggered the recursion protection of the
  function tracer. This will show where things need to be fixed as
  recursion slows down the function tracer.

  The eval enum mapping updates done at boot up are now offloaded to a
  work queue, as it caused a noticeable pause on slow embedded boards.

  Various clean ups and last minute fixes"

* tag 'trace-v5.11' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace: (33 commits)
  tracing: Offload eval map updates to a work queue
  Revert: "ring-buffer: Remove HAVE_64BIT_ALIGNED_ACCESS"
  ring-buffer: Add rb_check_bpage in __rb_allocate_pages
  ring-buffer: Fix two typos in comments
  tracing: Drop unneeded assignment in ring_buffer_resize()
  tracing: Disable ftrace selftests when any tracer is running
  seq_buf: Avoid type mismatch for seq_buf_init
  ring-buffer: Fix a typo in function description
  ring-buffer: Remove obsolete rb_event_is_commit()
  ring-buffer: Add test to validate the time stamp deltas
  ftrace/documentation: Fix RST C code blocks
  tracing: Clean up after filter logic rewriting
  tracing: Remove the useless value assignment in test_create_synth_event()
  livepatch: Use the default ftrace_ops instead of REGS when ARGS is available
  ftrace/x86: Allow for arguments to be passed in to ftrace_regs by default
  ftrace: Have the callbacks receive a struct ftrace_regs instead of pt_regs
  MAINTAINERS: assign ./fs/tracefs to TRACING
  tracing: Fix some typos in comments
  ftrace: Remove unused varible 'ret'
  ring-buffer: Add recording of ring buffer recursion into recursed_functions
  ...

1 files changed, 236 insertions, 0 deletions

diff --git a/kernel/trace/trace_recursion_record.c b/kernel/trace/trace_recursion_record.c
new file mode 100644
index 000000000000..b2edac1fe156
--- /dev/null
+++ b/kernel/trace/trace_recursion_record.c
@@ -0,0 +1,236 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/seq_file.h>
+#include <linux/kallsyms.h>
+#include <linux/module.h>
+#include <linux/ftrace.h>
+#include <linux/fs.h>
+
+#include "trace_output.h"
+
+struct recursed_functions {
+	unsigned long		ip;
+	unsigned long		parent_ip;
+};
+
+static struct recursed_functions recursed_functions[CONFIG_FTRACE_RECORD_RECURSION_SIZE];
+static atomic_t nr_records;
+
+/*
+ * Cache the last found function. Yes, updates to this is racey, but
+ * so is memory cache ;-)
+ */
+static unsigned long cached_function;
+
+void ftrace_record_recursion(unsigned long ip, unsigned long parent_ip)
+{
+	int index = 0;
+	int i;
+	unsigned long old;
+
+ again:
+	/* First check the last one recorded */
+	if (ip == cached_function)
+		return;
+
+	i = atomic_read(&nr_records);
+	/* nr_records is -1 when clearing records */
+	smp_mb__after_atomic();
+	if (i < 0)
+		return;
+
+	/*
+	 * If there's two writers and this writer comes in second,
+	 * the cmpxchg() below to update the ip will fail. Then this
+	 * writer will try again. It is possible that index will now
+	 * be greater than nr_records. This is because the writer
+	 * that succeeded has not updated the nr_records yet.
+	 * This writer could keep trying again until the other writer
+	 * updates nr_records. But if the other writer takes an
+	 * interrupt, and that interrupt locks up that CPU, we do
+	 * not want this CPU to lock up due to the recursion protection,
+	 * and have a bug report showing this CPU as the cause of
+	 * locking up the computer. To not lose this record, this
+	 * writer will simply use the next position to update the
+	 * recursed_functions, and it will update the nr_records
+	 * accordingly.
+	 */
+	if (index < i)
+		index = i;
+	if (index >= CONFIG_FTRACE_RECORD_RECURSION_SIZE)
+		return;
+
+	for (i = index - 1; i >= 0; i--) {
+		if (recursed_functions[i].ip == ip) {
+			cached_function = ip;
+			return;
+		}
+	}
+
+	cached_function = ip;
+
+	/*
+	 * We only want to add a function if it hasn't been added before.
+	 * Add to the current location before incrementing the count.
+	 * If it fails to add, then increment the index (save in i)
+	 * and try again.
+	 */
+	old = cmpxchg(&recursed_functions[index].ip, 0, ip);
+	if (old != 0) {
+		/* Did something else already added this for us? */
+		if (old == ip)
+			return;
+		/* Try the next location (use i for the next index) */
+		index++;
+		goto again;
+	}
+
+	recursed_functions[index].parent_ip = parent_ip;
+
+	/*
+	 * It's still possible that we could race with the clearing
+	 *    CPU0                                    CPU1
+	 *    ----                                    ----
+	 *                                       ip = func
+	 *  nr_records = -1;
+	 *  recursed_functions[0] = 0;
+	 *                                       i = -1
+	 *                                       if (i < 0)
+	 *  nr_records = 0;
+	 *  (new recursion detected)
+	 *      recursed_functions[0] = func
+	 *                                            cmpxchg(recursed_functions[0],
+	 *                                                    func, 0)
+	 *
+	 * But the worse that could happen is that we get a zero in
+	 * the recursed_functions array, and it's likely that "func" will
+	 * be recorded again.
+	 */
+	i = atomic_read(&nr_records);
+	smp_mb__after_atomic();
+	if (i < 0)
+		cmpxchg(&recursed_functions[index].ip, ip, 0);
+	else if (i <= index)
+		atomic_cmpxchg(&nr_records, i, index + 1);
+}
+EXPORT_SYMBOL_GPL(ftrace_record_recursion);
+
+static DEFINE_MUTEX(recursed_function_lock);
+static struct trace_seq *tseq;
+
+static void *recursed_function_seq_start(struct seq_file *m, loff_t *pos)
+{
+	void *ret = NULL;
+	int index;
+
+	mutex_lock(&recursed_function_lock);
+	index = atomic_read(&nr_records);
+	if (*pos < index) {
+		ret = &recursed_functions[*pos];
+	}
+
+	tseq = kzalloc(sizeof(*tseq), GFP_KERNEL);
+	if (!tseq)
+		return ERR_PTR(-ENOMEM);
+
+	trace_seq_init(tseq);
+
+	return ret;
+}
+
+static void *recursed_function_seq_next(struct seq_file *m, void *v, loff_t *pos)
+{
+	int index;
+	int p;
+
+	index = atomic_read(&nr_records);
+	p = ++(*pos);
+
+	return p < index ? &recursed_functions[p] : NULL;
+}
+
+static void recursed_function_seq_stop(struct seq_file *m, void *v)
+{
+	kfree(tseq);
+	mutex_unlock(&recursed_function_lock);
+}
+
+static int recursed_function_seq_show(struct seq_file *m, void *v)
+{
+	struct recursed_functions *record = v;
+	int ret = 0;
+
+	if (record) {
+		trace_seq_print_sym(tseq, record->parent_ip, true);
+		trace_seq_puts(tseq, ":\t");
+		trace_seq_print_sym(tseq, record->ip, true);
+		trace_seq_putc(tseq, '\n');
+		ret = trace_print_seq(m, tseq);
+	}
+
+	return ret;
+}
+
+static const struct seq_operations recursed_function_seq_ops = {
+	.start  = recursed_function_seq_start,
+	.next   = recursed_function_seq_next,
+	.stop   = recursed_function_seq_stop,
+	.show   = recursed_function_seq_show
+};
+
+static int recursed_function_open(struct inode *inode, struct file *file)
+{
+	int ret = 0;
+
+	mutex_lock(&recursed_function_lock);
+	/* If this file was opened for write, then erase contents */
+	if ((file->f_mode & FMODE_WRITE) && (file->f_flags & O_TRUNC)) {
+		/* disable updating records */
+		atomic_set(&nr_records, -1);
+		smp_mb__after_atomic();
+		memset(recursed_functions, 0, sizeof(recursed_functions));
+		smp_wmb();
+		/* enable them again */
+		atomic_set(&nr_records, 0);
+	}
+	if (file->f_mode & FMODE_READ)
+		ret = seq_open(file, &recursed_function_seq_ops);
+	mutex_unlock(&recursed_function_lock);
+
+	return ret;
+}
+
+static ssize_t recursed_function_write(struct file *file,
+				       const char __user *buffer,
+				       size_t count, loff_t *ppos)
+{
+	return count;
+}
+
+static int recursed_function_release(struct inode *inode, struct file *file)
+{
+	if (file->f_mode & FMODE_READ)
+		seq_release(inode, file);
+	return 0;
+}
+
+static const struct file_operations recursed_functions_fops = {
+	.open           = recursed_function_open,
+	.write		= recursed_function_write,
+	.read           = seq_read,
+	.llseek         = seq_lseek,
+	.release        = recursed_function_release,
+};
+
+__init static int create_recursed_functions(void)
+{
+	struct dentry *dentry;
+
+	dentry = trace_create_file("recursed_functions", 0644, NULL, NULL,
+				   &recursed_functions_fops);
+	if (!dentry)
+		pr_warn("WARNING: Failed to create recursed_functions\n");
+	return 0;
+}
+
+fs_initcall(create_recursed_functions);