Re: [PATCH v1 2/2] NFS: use unsigned long for req field in nfs_page_class

[Benjamin Coddington]

Hi Sean,

On 8 Apr 2026, at 12:14, Sean Chang wrote:

> The nfs_page_class tracepoint used a pointer for the req field. This
> caused Sparse to complain about dereferencing a pointer marked as
> __private within the trace ring buffer context.
>
> Change the field type to unsigned long to store the address of the
> request without dereferencing it. Update TP_printk to use 0x%lx for
> consistent hexadecimal output, allowing for unique identification of
> requests across the trace log.

Probably we don't want to bypass the %p formatting because some
configurations use it to obfuscate kernel pointers.

I think in this context the __private annotation is incorrect.  We deref the
nfs_page pointer only in TP_fast_assign() which runs at the call site, and
the TP_printk only outputs the pointer value.

cc: Jeff

Ben

>
> Signed-off-by: Sean Chang <seanwascoding@xxxxxxxxx>
> ---
>  fs/nfs/nfstrace.h | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/fs/nfs/nfstrace.h b/fs/nfs/nfstrace.h
> index 9f9ce4a565ea..4150bbd99cfa 100644
> --- a/fs/nfs/nfstrace.h
> +++ b/fs/nfs/nfstrace.h
> @@ -1496,7 +1496,7 @@ DECLARE_EVENT_CLASS(nfs_page_class,
>  			__field(dev_t, dev)
>  			__field(u32, fhandle)
>  			__field(u64, fileid)
> -			__field(const struct nfs_page *__private, req)
> +			__field(unsigned long, req)
>  			__field(loff_t, offset)
>  			__field(unsigned int, count)
>  			__field(unsigned long, flags)
> @@ -1509,14 +1509,14 @@ DECLARE_EVENT_CLASS(nfs_page_class,
>  			__entry->dev = inode->i_sb->s_dev;
>  			__entry->fileid = nfsi->fileid;
>  			__entry->fhandle = nfs_fhandle_hash(&nfsi->fh);
> -			__entry->req = req;
> +			__entry->req = (unsigned long)req;
>  			__entry->offset = req_offset(req);
>  			__entry->count = req->wb_bytes;
>  			__entry->flags = req->wb_flags;
>  		),
>
>  		TP_printk(
> -			"fileid=%02x:%02x:%llu fhandle=0x%08x req=%p offset=%lld count=%u flags=%s",
> +			"fileid=%02x:%02x:%llu fhandle=0x%08x req=0x%lx offset=%lld count=%u flags=%s",
>  			MAJOR(__entry->dev), MINOR(__entry->dev),
>  			(unsigned long long)__entry->fileid, __entry->fhandle,
>  			__entry->req, __entry->offset, __entry->count,
> -- 
> 2.34.1