linux-kernel - Re: [PATCH] f2fs: fix the assign logic of iocb

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Date:   Thu, 20 Oct 2022 17:01:16 +0800
From:   Chao Yu <chao@...nel.org>
To:     Mukesh Ojha <quic_mojha@...cinc.com>, jaegeuk@...nel.org,
        mhiramat@...nel.org
Cc:     linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] f2fs: fix the assign logic of iocb

On 2022/10/20 0:17, Mukesh Ojha wrote:
> commit 18ae8d12991b ("f2fs: show more DIO information in tracepoint")
> introduces iocb field in 'f2fs_direct_IO_enter' trace event
> And it only assigns the pointer and later it accesses its field
> in trace print log.
> 
> Fix it by correcting data type and memcpy the content of iocb.

So the implementation below is wrong, right? since it just assign __entry->name
with dentry->d_name.name rather than copyiny entirely, so that, during printing
of tracepoint, __entry->name may be invalid.

TRACE_EVENT(f2fs_unlink_enter,

	TP_PROTO(struct inode *dir, struct dentry *dentry),

	TP_ARGS(dir, dentry),

	TP_STRUCT__entry(
		__field(dev_t,	dev)
		__field(ino_t,	ino)
		__field(loff_t,	size)
		__field(blkcnt_t, blocks)
		__field(const char *,	name)
	),

	TP_fast_assign(
		__entry->dev	= dir->i_sb->s_dev;
		__entry->ino	= dir->i_ino;
		__entry->size	= dir->i_size;
		__entry->blocks	= dir->i_blocks;
		__entry->name	= dentry->d_name.name;
	),

> 
> Fixes: 18ae8d12991b ("f2fs: show more DIO information in tracepoint")
> Signed-off-by: Mukesh Ojha <quic_mojha@...cinc.com>
> ---
>   include/trace/events/f2fs.h | 10 +++++-----
>   1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/include/trace/events/f2fs.h b/include/trace/events/f2fs.h
> index c6b3724..7727ec9 100644
> --- a/include/trace/events/f2fs.h
> +++ b/include/trace/events/f2fs.h
> @@ -940,7 +940,7 @@ TRACE_EVENT(f2fs_direct_IO_enter,
>   	TP_STRUCT__entry(
>   		__field(dev_t,	dev)
>   		__field(ino_t,	ino)
> -		__field(struct kiocb *,	iocb)
> +		__field_struct(struct kiocb,	iocb)
>   		__field(unsigned long,	len)
>   		__field(int,	rw)
>   	),
> @@ -948,17 +948,17 @@ TRACE_EVENT(f2fs_direct_IO_enter,
>   	TP_fast_assign(
>   		__entry->dev	= inode->i_sb->s_dev;
>   		__entry->ino	= inode->i_ino;
> -		__entry->iocb	= iocb;
> +		 memcpy(&__entry->iocb, iocb, sizeof(*iocb));
>   		__entry->len	= len;
>   		__entry->rw	= rw;
>   	),
>   
>   	TP_printk("dev = (%d,%d), ino = %lu pos = %lld len = %lu ki_flags = %x ki_ioprio = %x rw = %d",
>   		show_dev_ino(__entry),
> -		__entry->iocb->ki_pos,
> +		__entry->iocb.ki_pos,
>   		__entry->len,
> -		__entry->iocb->ki_flags,
> -		__entry->iocb->ki_ioprio,
> +		__entry->iocb.ki_flags,
> +		__entry->iocb.ki_ioprio,
>   		__entry->rw)
>   );
>