linux-kernel - Re: [PATCH net-next v4] net/core: fix wrong return value in __splice

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Message-ID: <20250819020710.6681-1-hept.hept.hept@gmail.com>
Date: Tue, 19 Aug 2025 10:07:10 +0800
From: Pengtao He <hept.hept.hept@...il.com>
To: willemdebruijn.kernel@...il.com
Cc: aleksander.lobakin@...el.com,
	almasrymina@...gle.com,
	davem@...emloft.net,
	ebiggers@...gle.com,
	edumazet@...gle.com,
	hept.hept.hept@...il.com,
	horms@...nel.org,
	kerneljasonxing@...il.com,
	kuba@...nel.org,
	linux-kernel@...r.kernel.org,
	mhal@...x.co,
	netdev@...r.kernel.org,
	pabeni@...hat.com,
	willemb@...gle.com
Subject: Re: [PATCH net-next v4] net/core: fix wrong return value in __splice_segment

> Pengtao He wrote:
> > If *len is equal to 0 at the beginning of __splice_segment
> > it returns true directly. But when decreasing *len from
> > a positive number to 0 in __splice_segment, it returns false.
> > The caller needs to call __splice_segment again.
> > 
> > Recheck *len if it changes, return true in time.
> > Reduce unnecessary calls to __splice_segment.
> 
> Fix is a strong term. The existing behavior is correct, it just takes
> an extra pass through the loop in caller __skb_splice_bits. As also
> indicated by this patch targeting net-next.
> 
> I would suggest something like "net: avoid one loop iteration in __skb_splice_bits"

Thanks for the detailed and good suggestion. I will correct it.

> 
> 
> > Signed-off-by: Pengtao He <hept.hept.hept@...il.com>
> > ---
> > v4:
> > Correct the commit message.
> > v3:
> > Reduce once condition evaluation.
> > v2:
> > Correct the commit message and target tree.
> > v1:
> > https://lore.kernel.org/netdev/20250723063119.24059-1-hept.hept.hept@gmail.com/
> > ---
> >  net/core/skbuff.c | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> > 
> > diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> > index ee0274417948..23b776cd9879 100644
> > --- a/net/core/skbuff.c
> > +++ b/net/core/skbuff.c
> > @@ -3112,7 +3112,9 @@ static bool __splice_segment(struct page *page, unsigned int poff,
> >  		poff += flen;
> >  		plen -= flen;
> >  		*len -= flen;
> > -	} while (*len && plen);
> > +		if (!*len)
> > +			return true;
> > +	} while (plen);
> >  
> >  	return false;
> >  }
> > -- 
> > 2.49.0
> >