[PATCH v6 5/6] tracing: Show inode and device major:minor in deferred user space stacktrace

[Steven Rostedt <rostedt@kernel.org>]

From: Steven Rostedt <rostedt@goodmis.org>

The deferred user space stacktrace event already does a lookup of the vma
for each address in the trace to get the file offset for those addresses,
it can also report the file itself.

Add two more arrays to the user space stacktrace event. One for the inode
number, and the other to store the device major:minor number. Now the
output looks like this:

       trace-cmd-1108    [007] .....   240.253487: <user stack unwind>
cookie=7000000000009
 =>  <00000000001001ca> : 1340007 : 254:3
 =>  <000000000000ae27> : 1308548 : 254:3
 =>  <00000000000107e7> : 1440347 : 254:3
 =>  <00000000000109d3> : 1440347 : 254:3
 =>  <0000000000011523> : 1440347 : 254:3
 =>  <000000000001f79d> : 1440347 : 254:3
 =>  <000000000001fb01> : 1440347 : 254:3
 =>  <000000000001fbc0> : 1440347 : 254:3
 =>  <000000000000eb7e> : 1440347 : 254:3
 =>  <0000000000029ca8> : 1340007 : 254:3

Use space tooling can use this information to get the actual functions
from the files.

Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
Changes since v5: https://lore.kernel.org/20250424192613.869730948@goodmis.org

- Set inode to -1L if vma is not found for that address to let user space
  know that, and differentiate from a vdso section.

 kernel/trace/trace.c         | 26 +++++++++++++++++++++++++-
 kernel/trace/trace_entries.h |  8 ++++++--
 kernel/trace/trace_output.c  | 27 +++++++++++++++++++++++++++
 3 files changed, 58 insertions(+), 3 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 3e9ef644dd64..c6e1471e4615 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -3140,6 +3140,8 @@ static void trace_user_unwind_callback(struct unwind_work *unwind,
 	unsigned int trace_ctx;
 	struct vm_area_struct *vma = NULL;
 	unsigned long *caller;
+	unsigned long *inodes;
+	unsigned int *devs;
 	unsigned int offset;
 	int len;
 	int i;
@@ -3151,7 +3153,8 @@ static void trace_user_unwind_callback(struct unwind_work *unwind,
 	if (!(tr->trace_flags & TRACE_ITER_USERSTACKTRACE_DELAY))
 		return;
 
-	len = trace->nr * sizeof(unsigned long) + sizeof(*entry);
+	len = trace->nr * (sizeof(unsigned long) * 2 + sizeof(unsigned int))
+			   + sizeof(*entry);
 
 	trace_ctx = tracing_gen_ctx();
 
@@ -3172,6 +3175,15 @@ static void trace_user_unwind_callback(struct unwind_work *unwind,
 	entry->__data_loc_stack = offset | (len << 16);
 	caller = (void *)entry + offset;
 
+	offset += len;
+	entry->__data_loc_inodes = offset | (len << 16);
+	inodes = (void *)entry + offset;
+
+	offset += len;
+	len = sizeof(unsigned int) * trace->nr;
+	entry->__data_loc_dev = offset | (len << 16);
+	devs = (void *)entry + offset;
+
 	for (i = 0; i < trace->nr; i++) {
 		unsigned long addr = trace->entries[i];
 
@@ -3180,9 +3192,21 @@ static void trace_user_unwind_callback(struct unwind_work *unwind,
 
 		if (!vma) {
 			caller[i] = addr;
+			/* Use -1 to denote no vma found */
+			inodes[i] = -1L;
+			devs[i] = 0;
 			continue;
 		}
+
 		caller[i] = (addr - vma->vm_start) + (vma->vm_pgoff << PAGE_SHIFT);
+
+		if (vma->vm_file && vma->vm_file->f_inode) {
+			inodes[i] = vma->vm_file->f_inode->i_ino;
+			devs[i] = vma->vm_file->f_inode->i_sb->s_dev;
+		} else {
+			inodes[i] = 0;
+			devs[i] = 0;
+		}
 	}
 
 	__buffer_unlock_commit(buffer, event);
diff --git a/kernel/trace/trace_entries.h b/kernel/trace/trace_entries.h
index 40dc53ead0a8..5f7b72359901 100644
--- a/kernel/trace/trace_entries.h
+++ b/kernel/trace/trace_entries.h
@@ -256,10 +256,14 @@ FTRACE_ENTRY(user_unwind_stack, userunwind_stack_entry,
 	F_STRUCT(
 		__field(		u64,		cookie	)
 		__dynamic_array(	unsigned long,	stack	)
+		__dynamic_array(	unsigned long,	inodes	)
+		__dynamic_array(	unsigned int,	dev	)
 	),
 
-	F_printk("cookie=%lld\n%s", __entry->cookie,
-		 __print_dynamic_array(stack, sizeof(unsigned long)))
+	F_printk("cookie=%lld\n%s%s%s", __entry->cookie,
+		 __print_dynamic_array(stack, sizeof(unsigned long)),
+		 __print_dynamic_array(inodes, sizeof(unsigned long)),
+		 __print_dynamic_array(dev, sizeof(unsigned long)))
 );
 
 FTRACE_ENTRY(user_unwind_cookie, userunwind_cookie_entry,
diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
index 9489537533f7..437e5f23b73d 100644
--- a/kernel/trace/trace_output.c
+++ b/kernel/trace/trace_output.c
@@ -1410,9 +1410,13 @@ static enum print_line_t trace_user_unwind_stack_print(struct trace_iterator *it
 	struct userunwind_stack_entry *field;
 	struct trace_seq *s = &iter->seq;
 	unsigned long *caller;
+	unsigned long *inodes;
+	unsigned int *devs;
 	unsigned int offset;
 	unsigned int len;
 	unsigned int caller_cnt;
+	unsigned int inode_cnt;
+	unsigned int dev_cnt;
 	unsigned int i;
 
 	trace_assign_type(field, iter->ent);
@@ -1429,6 +1433,21 @@ static enum print_line_t trace_user_unwind_stack_print(struct trace_iterator *it
 
 	caller = (void *)iter->ent + offset;
 
+	/* The inodes and devices are also dynamic pointers */
+	offset = field->__data_loc_inodes;
+	len = offset >> 16;
+	offset = offset & 0xffff;
+	inode_cnt = len / sizeof(*inodes);
+
+	inodes = (void *)iter->ent + offset;
+
+	offset = field->__data_loc_dev;
+	len = offset >> 16;
+	offset = offset & 0xffff;
+	dev_cnt = len / sizeof(*devs);
+
+	devs = (void *)iter->ent + offset;
+
 	for (i = 0; i < caller_cnt; i++) {
 		unsigned long ip = caller[i];
 
@@ -1437,6 +1456,14 @@ static enum print_line_t trace_user_unwind_stack_print(struct trace_iterator *it
 
 		trace_seq_puts(s, " => ");
 		seq_print_user_ip(s, NULL, ip, flags);
+
+		if (i < inode_cnt) {
+			trace_seq_printf(s, " : %ld", inodes[i]);
+			if (i < dev_cnt) {
+				trace_seq_printf(s, " : %d:%d",
+						 MAJOR(devs[i]), MINOR(devs[i]));
+			}
+		}
 		trace_seq_putc(s, '\n');
 	}
 
-- 
2.50.1