[Linaro-mm-sig] Re: [PATCH v2] dma-buf: add some tracepoints to debug.

On Wed, 26 Nov 2025 00:29:49 +0800 Xiang Gao gxxa03070307@gmail.com wrote:

+++ b/include/trace/events/dma_buf.h @@ -0,0 +1,281 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#undef TRACE_SYSTEM +#define TRACE_SYSTEM dma_buf

+#if !defined(_TRACE_DMA_BUF_H) || defined(TRACE_HEADER_MULTI_READ) +#define _TRACE_DMA_BUF_H

+#include <linux/dma-buf.h> +#include <linux/tracepoint.h>

+TRACE_EVENT(dma_buf_export,

• 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);
  

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>