From: Steven Rostedt <rostedt@goodmis.org>

Add specific reporting of the futex system call. This allows for debugging
the futex code a bit easier. Instead of just showing the values passed
into the futex system call, read the value of the user space memory
pointed to by the addr parameter.

Also make the op parameter more readable by parsing the values to show
what the command is:

 futex_requeue_p-3251    [002] .....  2101.068479: sys_futex(uaddr: 0x55e79a4da834 (0x80000cb1), FUTEX_LOCK_PI|FUTEX_PRIVATE_FLAG, val: 0)
 futex_requeue_p-3248    [001] .....  2101.068970: sys_futex(uaddr: 0x7f859072f990 (0xcb2), FUTEX_WAIT_BITSET|FUTEX_CLOCK_REALTIME, val: 3250)
 futex_requeue_p-3252    [005] .....  2101.069108: sys_futex(uaddr: 0x55e79a4da838 (0), FUTEX_WAIT_REQUEUE_PI|FUTEX_PRIVATE_FLAG, val: 0, timespec: 0x7ffe61076aa0, uaddr2: 0x55e79a4da834, uaddr2: 94453214586932, val3: 0)
 futex_requeue_p-3252    [005] .....  2101.069410: sys_futex(uaddr: 0x55e79a4da834 (0x80000cb1), FUTEX_LOCK_PI|FUTEX_PRIVATE_FLAG, val: 0)

Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
Changes since v2: https://patch.msgid.link/20260310201036.542627924@kernel.org

- Removed unused "buf" variable (kernel test robot)

- Iterate __futex_cmds[] make the print statement.
  Note this required exposing __futex_cmds[] to trace_syscall.c

- Added back val statement (with the move to futex/syscall.c the
  third parameter was dropped).

 include/linux/futex.h         |   8 +-
 kernel/futex/syscalls.c       |  97 +++++++++++++++++++++++
 kernel/trace/trace_syscalls.c | 144 +++++++++++++++++++++++++++++++++-
 3 files changed, 245 insertions(+), 4 deletions(-)

diff --git a/include/linux/futex.h b/include/linux/futex.h
index 9e9750f04980..7eaf01ff68cf 100644
--- a/include/linux/futex.h
+++ b/include/linux/futex.h
@@ -82,6 +82,11 @@ long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
 	      u32 __user *uaddr2, u32 val2, u32 val3);
 int futex_hash_prctl(unsigned long arg2, unsigned long arg3, unsigned long arg4);
 
+#ifdef CONFIG_FTRACE_SYSCALLS
+void futex_print_syscall(struct seq_buf *s, int nr_args, unsigned long *args, u32 *ptr);
+extern const char * __futex_cmds[];
+#endif
+
 #ifdef CONFIG_FUTEX_PRIVATE_HASH
 int futex_hash_allocate_default(void);
 void futex_hash_free(struct mm_struct *mm);
@@ -114,7 +119,8 @@ static inline int futex_hash_allocate_default(void)
 }
 static inline int futex_hash_free(struct mm_struct *mm) { return 0; }
 static inline int futex_mm_init(struct mm_struct *mm) { return 0; }
-
+static inline void futex_print_syscall(struct seq_buf *s, int nr_args,
+				       unsigned long *args, u32 *ptr) { }
 #endif
 
 #endif
diff --git a/kernel/futex/syscalls.c b/kernel/futex/syscalls.c
index 743c7a728237..3ba8ca017c9c 100644
--- a/kernel/futex/syscalls.c
+++ b/kernel/futex/syscalls.c
@@ -171,6 +171,18 @@ static __always_inline bool futex_cmd_has_timeout(u32 cmd)
 	return false;
 }
 
+static __always_inline bool futex_cmd_has_addr2(u32 cmd)
+{
+	switch (cmd) {
+	case FUTEX_REQUEUE:
+	case FUTEX_CMP_REQUEUE:
+	case FUTEX_WAKE_OP:
+	case FUTEX_WAIT_REQUEUE_PI:
+		return true;
+	}
+	return false;
+}
+
 static __always_inline int
 futex_init_timeout(u32 cmd, u32 op, struct timespec64 *ts, ktime_t *t)
 {
@@ -207,6 +219,91 @@ SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
 	return do_futex(uaddr, op, val, tp, uaddr2, (unsigned long)utime, val3);
 }
 
+#ifdef CONFIG_FTRACE_SYSCALLS
+
+/* End with NULL for iterators */
+const char * __futex_cmds[] =
+{
+	"FUTEX_WAIT", "FUTEX_WAKE", "FUTEX_FD", "FUTEX_REQUEUE",
+	"FUTEX_CMP_REQUEUE", "FUTEX_WAKE_OP", "FUTEX_LOCK_PI",
+	"FUTEX_UNLOCK_PI", "FUTEX_TRYLOCK_PI", "FUTEX_WAIT_BITSET",
+	"FUTEX_WAKE_BITSET", "FUTEX_WAIT_REQUEUE_PI", "FUTEX_CMP_REQUEUE_PI",
+	"FUTEX_LOCK_PI2", NULL
+};
+
+void futex_print_syscall(struct seq_buf *s, int nr_args, unsigned long *args, u32 *ptr)
+{
+	unsigned int op, cmd;
+	bool done = false;
+
+	for (int i = 0; !done && i < nr_args; i++) {
+
+		if (seq_buf_has_overflowed(s))
+			break;
+
+		switch (i) {
+		case 0:
+			seq_buf_printf(s, "uaddr: 0x%lx", args[i]);
+			if (ptr) {
+				u32 val = *ptr;
+				if (val < 10)
+					seq_buf_printf(s, " (%u)", val);
+				else
+					seq_buf_printf(s, " (0x%x)", val);
+			}
+			continue;
+		case 1:
+			op = args[i];
+			cmd = op & FUTEX_CMD_MASK;
+			if (cmd <= FUTEX_LOCK_PI2)
+				seq_buf_printf(s, ", %s", __futex_cmds[cmd]);
+			else
+				seq_buf_puts(s, ", UNKNOWN");
+
+			if (op & FUTEX_PRIVATE_FLAG)
+				seq_buf_puts(s, "|FUTEX_PRIVATE_FLAG");
+			if (op & FUTEX_CLOCK_REALTIME)
+				seq_buf_puts(s, "|FUTEX_CLOCK_REALTIME");
+			continue;
+		case 2:
+			if (args[i] < 10)
+				seq_buf_printf(s, ", val: %ld", args[i]);
+			else
+				seq_buf_printf(s, ", val: 0x%lx", args[i]);
+			continue;
+		case 3:
+			if (!futex_cmd_has_timeout(cmd)) {
+
+				if (!futex_cmd_has_addr2(cmd)) {
+					done = true;
+					continue;
+				}
+
+				seq_buf_printf(s, ", val2: 0x%x", (u32)(long)args[i]);
+				continue;
+			}
+
+			if (!args[i])
+				continue;
+
+			seq_buf_printf(s, ", timespec: 0x%lx", args[i]);
+			continue;
+		case 4:
+			if (!futex_cmd_has_addr2(cmd)) {
+				done = true;
+				continue;
+			}
+			seq_buf_printf(s, ", uaddr2: 0x%lx", args[i]);
+			continue;
+		case 5:
+			seq_buf_printf(s, ", val3: %lu", args[i]);
+			done = true;
+			continue;
+		}
+	}
+}
+#endif
+
 /**
  * futex_parse_waitv - Parse a waitv array from userspace
  * @futexv:	Kernel side list of waiters to be filled
diff --git a/kernel/trace/trace_syscalls.c b/kernel/trace/trace_syscalls.c
index 37317b81fcda..f8213d772f89 100644
--- a/kernel/trace/trace_syscalls.c
+++ b/kernel/trace/trace_syscalls.c
@@ -6,11 +6,13 @@
 #include <linux/slab.h>
 #include <linux/kernel.h>
 #include <linux/module.h>	/* for MODULE_NAME_LEN via KSYM_SYMBOL_LEN */
+#include <linux/futex.h>
 #include <linux/ftrace.h>
 #include <linux/perf_event.h>
 #include <linux/xarray.h>
 #include <asm/syscall.h>
 
+
 #include "trace_output.h"
 #include "trace.h"
 
@@ -237,6 +239,27 @@ sys_enter_openat_print(struct syscall_trace_enter *trace, struct syscall_metadat
 	return trace_handle_return(s);
 }
 
+static enum print_line_t
+sys_enter_futex_print(struct syscall_trace_enter *trace, struct syscall_metadata *entry,
+		      struct trace_seq *s, struct trace_event *event, int ent_size)
+{
+	void *end = (void *)trace + ent_size;
+	void *ptr;
+
+	/* Set ptr to the user space copied area */
+	ptr = (void *)trace->args + sizeof(unsigned long) * entry->nb_args;
+	if (ptr + 4 > end)
+		ptr = NULL;
+
+	trace_seq_printf(s, "%s(", entry->name);
+
+	futex_print_syscall(&s->seq, entry->nb_args, trace->args, ptr);
+
+	trace_seq_puts(s, ")\n");
+
+	return trace_handle_return(s);
+}
+
 static enum print_line_t
 print_syscall_enter(struct trace_iterator *iter, int flags,
 		    struct trace_event *event)
@@ -267,6 +290,10 @@ print_syscall_enter(struct trace_iterator *iter, int flags,
 		if (!tr || !(tr->trace_flags & TRACE_ITER(VERBOSE)))
 			return sys_enter_openat_print(trace, entry, s, event);
 		break;
+	case __NR_futex:
+		if (!tr || !(tr->trace_flags & TRACE_ITER(VERBOSE)))
+			return sys_enter_futex_print(trace, entry, s, event, iter->ent_size);
+		break;
 	default:
 		break;
 	}
@@ -437,6 +464,48 @@ sys_enter_openat_print_fmt(struct syscall_metadata *entry, char *buf, int len)
 	return pos;
 }
 
+static int __init
+sys_enter_futex_print_fmt(struct syscall_metadata *entry, char *buf, int len)
+{
+	int pos = 0;
+
+	pos += snprintf(buf + pos, LEN_OR_ZERO,
+			"\"uaddr: 0x%%lx (0x%%lx) cmd=%%s%%s%%s");
+	pos += snprintf(buf + pos, LEN_OR_ZERO,
+			"  val: 0x%%x timeout/val2: 0x%%llx");
+	pos += snprintf(buf + pos, LEN_OR_ZERO,
+			" uaddr2: 0x%%lx val3: 0x%%x\", ");
+
+	pos += snprintf(buf + pos, LEN_OR_ZERO,
+			" REC->uaddr,");
+	pos += snprintf(buf + pos, LEN_OR_ZERO,
+			" REC->__value,");
+	pos += snprintf(buf + pos, LEN_OR_ZERO,
+			"  __print_symbolic(REC->op & 0x%x, ", FUTEX_CMD_MASK);
+
+	for (int i = 0; __futex_cmds[i]; i++) {
+		pos += snprintf(buf + pos, LEN_OR_ZERO,
+				"%s{%d, \"%s\"} ",
+				i ? "," : "", i, __futex_cmds[i]);
+	}
+
+	pos += snprintf(buf + pos, LEN_OR_ZERO, "), ");
+
+	pos += snprintf(buf + pos, LEN_OR_ZERO,
+			" (REC->op & %d) ? \"|FUTEX_PRIVATE_FLAG\" : \"\",",
+			FUTEX_PRIVATE_FLAG);
+	pos += snprintf(buf + pos, LEN_OR_ZERO,
+			" (REC->op & %d) ? \"|FUTEX_CLOCK_REALTIME\" : \"\",",
+			FUTEX_CLOCK_REALTIME);
+
+	pos += snprintf(buf + pos, LEN_OR_ZERO,
+			" REC->val, REC->utime,");
+
+	pos += snprintf(buf + pos, LEN_OR_ZERO,
+			" REC->uaddr, REC->val3");
+	return pos;
+}
+
 static int __init
 __set_enter_print_fmt(struct syscall_metadata *entry, char *buf, int len)
 {
@@ -447,6 +516,8 @@ __set_enter_print_fmt(struct syscall_metadata *entry, char *buf, int len)
 	switch (entry->syscall_nr) {
 	case __NR_openat:
 		return sys_enter_openat_print_fmt(entry, buf, len);
+	case __NR_futex:
+		return sys_enter_futex_print_fmt(entry, buf, len);
 	default:
 		break;
 	}
@@ -523,6 +594,21 @@ static void __init free_syscall_print_fmt(struct trace_event_call *call)
 		kfree(call->print_fmt);
 }
 
+static int __init futex_fields(struct trace_event_call *call, int offset)
+{
+	char *arg;
+	int ret;
+
+	arg = kstrdup("__value", GFP_KERNEL);
+	if (WARN_ON_ONCE(!arg))
+		return -ENOMEM;
+	ret = trace_define_field(call, "u32", arg, offset, sizeof(int), 0,
+				 FILTER_OTHER);
+	if (ret)
+		kfree(arg);
+	return ret;
+}
+
 static int __init syscall_enter_define_fields(struct trace_event_call *call)
 {
 	struct syscall_trace_enter trace;
@@ -544,6 +630,9 @@ static int __init syscall_enter_define_fields(struct trace_event_call *call)
 		offset += sizeof(unsigned long);
 	}
 
+	if (!ret && meta->syscall_nr == __NR_futex)
+		return futex_fields(call, offset);
+
 	if (ret || !meta->user_mask)
 		return ret;
 
@@ -689,6 +778,45 @@ static int syscall_copy_user_array(char *buf, const char __user *ptr,
 	return 0;
 }
 
+static int
+syscall_get_futex(unsigned long *args, char **buffer, int *size, int buf_size)
+{
+	struct syscall_user_buffer *sbuf;
+	const char __user *ptr;
+
+	/* buf_size of zero means user doesn't want user space read */
+	if (!buf_size)
+		return -1;
+
+	/* If the syscall_buffer is NULL, tracing is being shutdown */
+	sbuf = READ_ONCE(syscall_buffer);
+	if (!sbuf)
+		return -1;
+
+	ptr = (char __user *)args[0];
+
+	*buffer = trace_user_fault_read(&sbuf->buf, ptr, 4, NULL, NULL);
+	if (!*buffer)
+		return -1;
+
+	/* Add room for the value */
+	*size += 4;
+
+	return 0;
+}
+
+static void syscall_put_futex(struct syscall_metadata *sys_data,
+			      struct syscall_trace_enter *entry,
+			      char *buffer)
+{
+	u32 *ptr;
+
+	/* Place the futex key into the storage */
+	ptr = (void *)entry->args + sizeof(unsigned long) * sys_data->nb_args;
+
+	*ptr = *(u32 *)buffer;
+}
+
 static char *sys_fault_user(unsigned int buf_size,
 			    struct syscall_metadata *sys_data,
 			    struct syscall_user_buffer *sbuf,
@@ -905,6 +1033,9 @@ static void ftrace_syscall_enter(void *data, struct pt_regs *regs, long id)
 		if (syscall_get_data(sys_data, args, &user_ptr,
 				     &size, user_sizes, &uargs, tr->syscall_buf_sz) < 0)
 			return;
+	} else if (syscall_nr == __NR_futex) {
+		if (syscall_get_futex(args, &user_ptr, &size, tr->syscall_buf_sz) < 0)
+			return;
 	}
 
 	size += sizeof(*entry) + sizeof(unsigned long) * sys_data->nb_args;
@@ -921,6 +1052,9 @@ static void ftrace_syscall_enter(void *data, struct pt_regs *regs, long id)
 	if (mayfault)
 		syscall_put_data(sys_data, entry, user_ptr, size, user_sizes, uargs);
 
+	else if (syscall_nr == __NR_futex)
+		syscall_put_futex(sys_data, entry, user_ptr);
+
 	trace_event_buffer_commit(&fbuffer);
 }
 
@@ -971,14 +1105,18 @@ static int reg_event_syscall_enter(struct trace_event_file *file,
 {
 	struct syscall_metadata *sys_data = call->data;
 	struct trace_array *tr = file->tr;
+	bool enable_faults;
 	int ret = 0;
 	int num;
 
 	num = sys_data->syscall_nr;
 	if (WARN_ON_ONCE(num < 0 || num >= NR_syscalls))
 		return -ENOSYS;
+
+	enable_faults = sys_data->user_mask || num == __NR_futex;
+
 	guard(mutex)(&syscall_trace_lock);
-	if (sys_data->user_mask) {
+	if (enable_faults) {
 		ret = syscall_fault_buffer_enable();
 		if (ret < 0)
 			return ret;
@@ -986,7 +1124,7 @@ static int reg_event_syscall_enter(struct trace_event_file *file,
 	if (!tr->sys_refcount_enter) {
 		ret = register_trace_sys_enter(ftrace_syscall_enter, tr);
 		if (ret < 0) {
-			if (sys_data->user_mask)
+			if (enable_faults)
 				syscall_fault_buffer_disable();
 			return ret;
 		}
@@ -1011,7 +1149,7 @@ static void unreg_event_syscall_enter(struct trace_event_file *file,
 	WRITE_ONCE(tr->enter_syscall_files[num], NULL);
 	if (!tr->sys_refcount_enter)
 		unregister_trace_sys_enter(ftrace_syscall_enter, tr);
-	if (sys_data->user_mask)
+	if (sys_data->user_mask || num == __NR_futex)
 		syscall_fault_buffer_disable();
 }
 
-- 
2.51.0