On Wed, 26 Nov 2025 00:29:49 +0800
Xiang Gao [off-list ref] wrote:

The above isn't doing what you think it's doing. The name is assigned
before this by the above __string(name, dmabuf->name).

You really shouldn't be taking any locks in a tracepoint. A tracepoint is a
callback, that isn't called most of the time. You could be hiding very
hard to find deadlocks by taking a lock in a tracepoint callback.

You need to take the lock around the tracepoint call itself where it is
called in the code. Not in the TRACE_EVENT.

You may need to have something like:

@@ -220,6 +223,8 @@ static int dma_buf_mmap_internal(struct file *file, struct vm_area_struct *vma)
 	    dmabuf->size >> PAGE_SHIFT)
 		return -EINVAL;

+	if (trace_dma_buf_mmap_internal_enabled()) {
+		guard(spinlock)(&dmabuf->namelock);
+		trace_dma_buf_mmap_internal(dmabuf);
+	}
+
 	return dmabuf->ops->mmap(dmabuf, vma);
 }

The "trace_dma_buf_mmap_internal_enabled()" is a static branch, where it is
either a nop or a jump to the tracing code. It's not a normal conditional
branch. It acts the same as tracepoints themselves do.

+		__entry->size = dmabuf->size;
+		__entry->ino = dmabuf->file->f_inode->i_ino;
+		__entry->f_refcnt = file_count(dmabuf->file);
+	),
+
+	TP_printk("exp_name=%s name=%s size=%zu ino=%lu f_refcnt=%ld",
+		  __get_str(exp_name),
+		  __get_str(name),
+		  __entry->size,
+		  __entry->ino,
+		  __entry->f_refcnt)
+);

Below seems to be a lot of very similar TRACE_EVENT()s. A TRACE_EVENT() is
literally defined as:

#define TRACE_EVENT(name, proto, args, tstruct, assign, print) \
	DECLARE_EVENT_CLASS(name,			       \
			     PARAMS(proto),		       \
			     PARAMS(args),		       \
			     PARAMS(tstruct),		       \
			     PARAMS(assign),		       \
			     PARAMS(print));		       \
	DEFINE_EVENT(name, name, PARAMS(proto), PARAMS(args));

That is, it is both a DECLARE_EVENT_CLASS() and a DEFINE_EVENT(). You can
make one DECLARE_EVENT_CLASS() and use many DEFINE_EVENT()s with it.

Each DECLARE_EVENT_CLASS() takes up around 4 to 5 kilobytes of memory. Each
DEFINE_EVENT() takes around 300 bytes to 1K of memory. The more
DEFINE_EVENT()s you use with a single DECLARE_EVENT_CLASS(), the more
memory you save. Please try to do that.

-- Steve

+
+TRACE_EVENT(dma_buf_fd,
+
+	TP_PROTO(struct dma_buf *dmabuf, int fd),
+
+	TP_ARGS(dmabuf, fd),
+
+	TP_STRUCT__entry(
+		__string(exp_name, dmabuf->exp_name)
+		__string(name, dmabuf->name)
+		__field(size_t, size)
+		__field(ino_t, ino)
+		__field(int, fd)
+		__field(long, f_refcnt)
+	),
+
+	TP_fast_assign(
+		__assign_str(exp_name);
+		spin_lock(&dmabuf->name_lock);
+		__assign_str(name);
+		spin_unlock(&dmabuf->name_lock);
+		__entry->size = dmabuf->size;
+		__entry->ino = dmabuf->file->f_inode->i_ino;
+		__entry->fd = fd;
+		__entry->f_refcnt = file_count(dmabuf->file);
+	),
+
+	TP_printk("exp_name=%s name=%s size=%zu ino=%lu fd=%d f_refcnt=%ld",
+		  __get_str(exp_name),
+		  __get_str(name),
+		  __entry->size,
+		  __entry->ino,
+		  __entry->fd,
+		  __entry->f_refcnt)
+);
+
+TRACE_EVENT(dma_buf_mmap_internal,
+
+	TP_PROTO(struct dma_buf *dmabuf),
+
+	TP_ARGS(dmabuf),
+
+	TP_STRUCT__entry(
+		__string(exp_name, dmabuf->exp_name)
+		__string(name, dmabuf->name)
+		__field(size_t, size)
+		__field(ino_t, ino)
+		__field(long, f_refcnt)
+	),
+
+	TP_fast_assign(
+		__assign_str(exp_name);
+		spin_lock(&dmabuf->name_lock);
+		__assign_str(name);
+		spin_unlock(&dmabuf->name_lock);
+		__entry->size = dmabuf->size;
+		__entry->ino = dmabuf->file->f_inode->i_ino;
+		__entry->f_refcnt = file_count(dmabuf->file);
+	),
+
+	TP_printk("exp_name=%s name=%s size=%zu ino=%lu f_refcnt=%ld",
+		  __get_str(exp_name),
+		  __get_str(name),
+		  __entry->size,
+		  __entry->ino,
+		  __entry->f_refcnt)
+);
+
+TRACE_EVENT(dma_buf_mmap,
+
+	TP_PROTO(struct dma_buf *dmabuf),
+
+	TP_ARGS(dmabuf),
+
+	TP_STRUCT__entry(
+		__string(exp_name, dmabuf->exp_name)
+		__string(name, dmabuf->name)
+		__field(size_t, size)
+		__field(ino_t, ino)
+		__field(long, f_refcnt)
+	),
+
+	TP_fast_assign(
+		__assign_str(exp_name);
+		spin_lock(&dmabuf->name_lock);
+		__assign_str(name);
+		spin_unlock(&dmabuf->name_lock);
+		__entry->size = dmabuf->size;
+		__entry->ino = dmabuf->file->f_inode->i_ino;
+		__entry->f_refcnt = file_count(dmabuf->file);
+	),
+
+	TP_printk("exp_name=%s name=%s size=%zu ino=%lu f_refcnt=%ld",
+		  __get_str(exp_name),
+		  __get_str(name),
+		  __entry->size,
+		  __entry->ino,
+		  __entry->f_refcnt)
+);
+
+TRACE_EVENT(dma_buf_attach,
+
+	TP_PROTO(struct dma_buf *dmabuf, struct device *dev),
+
+	TP_ARGS(dmabuf, dev),
+
+	TP_STRUCT__entry(
+		__string(dname, dev_name(dev))
+		__string(exp_name, dmabuf->exp_name)
+		__string(name, dmabuf->name)
+		__field(size_t, size)
+		__field(ino_t, ino)
+		__field(long, f_refcnt)
+	),
+
+	TP_fast_assign(
+		__assign_str(dname);
+		__assign_str(exp_name);
+		spin_lock(&dmabuf->name_lock);
+		__assign_str(name);
+		spin_unlock(&dmabuf->name_lock);
+		__entry->size = dmabuf->size;
+		__entry->ino = dmabuf->file->f_inode->i_ino;
+		__entry->f_refcnt = file_count(dmabuf->file);
+	),
+
+	TP_printk("dev_name=%s exp_name=%s name=%s size=%zu ino=%lu f_refcnt=%ld",
+		  __get_str(dname),
+		  __get_str(exp_name),
+		  __get_str(name),
+		  __entry->size,
+		  __entry->ino,
+		  __entry->f_refcnt)
+);
+
+TRACE_EVENT(dma_buf_detach,
+
+	TP_PROTO(struct dma_buf *dmabuf),
+
+	TP_ARGS(dmabuf),
+
+	TP_STRUCT__entry(
+		__string(exp_name, dmabuf->exp_name)
+		__string(name, dmabuf->name)
+		__field(size_t, size)
+		__field(ino_t, ino)
+		__field(long, f_refcnt)
+	),
+
+	TP_fast_assign(
+		__assign_str(exp_name);
+		spin_lock(&dmabuf->name_lock);
+		__assign_str(name);
+		spin_unlock(&dmabuf->name_lock);
+		__entry->size = dmabuf->size;
+		__entry->ino = dmabuf->file->f_inode->i_ino;
+		__entry->f_refcnt = file_count(dmabuf->file);
+	),
+
+	TP_printk("exp_name=%s name=%s size=%zu ino=%lu f_refcnt=%ld",
+		  __get_str(exp_name),
+		  __get_str(name),
+		  __entry->size,
+		  __entry->ino,
+		  __entry->f_refcnt)
+);
+
+TRACE_EVENT(dma_buf_get,
+
+	TP_PROTO(int fd, struct file *file),
+
+	TP_ARGS(fd, file),
+
+	TP_STRUCT__entry(
+		__string(exp_name, ((struct dma_buf *)file->private_data)->exp_name)
+		__string(name, ((struct dma_buf *)file->private_data)->name)
+		__field(size_t, size)
+		__field(ino_t, ino)
+		__field(int, fd)
+		__field(long, f_refcnt)
+	),
+
+	TP_fast_assign(
+		struct dma_buf *dmabuf = (struct dma_buf *)file->private_data;
+
+		__assign_str(exp_name);
+		spin_lock(&dmabuf->name_lock);
+		__assign_str(name);
+		spin_unlock(&dmabuf->name_lock);
+		__entry->size = dmabuf->size;
+		__entry->ino = dmabuf->file->f_inode->i_ino;
+		__entry->fd = fd;
+		__entry->f_refcnt = file_count(file);
+	),
+
+	TP_printk("exp_name=%s name=%s size=%zu ino=%lu fd=%d f_refcnt=%ld",
+		  __get_str(exp_name),
+		  __get_str(name),
+		  __entry->size,
+		  __entry->ino,
+		  __entry->fd,
+		  __entry->f_refcnt)
+);
+
+TRACE_EVENT(dma_buf_put,
+
+	TP_PROTO(struct dma_buf *dmabuf),
+
+	TP_ARGS(dmabuf),
+
+	TP_STRUCT__entry(
+		__string(exp_name, dmabuf->exp_name)
+		__string(name, dmabuf->name)
+		__field(size_t, size)
+		__field(ino_t, ino)
+		__field(long, f_refcnt)
+	),
+
+	TP_fast_assign(
+		__assign_str(exp_name);
+		spin_lock(&dmabuf->name_lock);
+		__assign_str(name);
+		spin_unlock(&dmabuf->name_lock);
+		__entry->size = dmabuf->size;
+		__entry->ino = dmabuf->file->f_inode->i_ino;
+		__entry->f_refcnt = file_count(dmabuf->file);
+	),
+
+	TP_printk("exp_name=%s name=%s size=%zu ino=%lu f_refcnt=%ld",
+		  __get_str(exp_name),
+		  __get_str(name),
+		  __entry->size,
+		  __entry->ino,
+		  __entry->f_refcnt)
+);
+
+#endif /* _TRACE_DMA_BUF_H */
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>