Re: [PATCH 07/17] net: convert sock.sk_wmem_alloc from atomic_t to refcount_t

[David Woodhouse <dwmw2@infradead.org>]

On Fri, 2018-06-15 at 14:44 +0100, David Woodhouse wrote:
> 
> > Or simply use a new field in ATM_SKB(skb) to remember a stable
> > truesize used in both sides (add/sub)
> 
> Right, that was my second suggestion ("copy the accounted value...").
> 
> It's a bit of a hack, and I think that actually *using* sock_wfree()
> instead of what's currently in atm_pop_raw() would be the better
> solution. Does anyone remember why we didn't do that in the first
> place?

That does end up being quite hairy. I don't think it's worth doing.

This should probably suffice to fix it...

Kevin this is going to conflict with the ifx_atm_alloc_skb() hack in
the tree you're working on, but that needs to be killed with fire
anyway. It's utterly pointless as discussed. 



>From 3368eaeb0a2f09138894dde0f26f879e5228005a Mon Sep 17 00:00:00 2001
From: David Woodhouse <dwmw2@infradead.org>
Date: Fri, 15 Jun 2018 20:49:20 +0100
Subject: [PATCH] atm: Preserve value of skb->truesize when accounting to vcc

There's a hack in pskb_expand_head() to avoid adjusting skb->truesize
for certain skbs. Ideally it would cover ATM too. It doesn't. Just
stashing the accounted value and using it in atm_raw_pop() is probably
the easiest way to cope.

Signed-off-by: David Woodhouse <dwmw2@infradead.org>
---
 include/linux/atmdev.h | 15 +++++++++++++++
 net/atm/br2684.c       |  3 +--
 net/atm/clip.c         |  3 +--
 net/atm/common.c       |  3 +--
 net/atm/lec.c          |  3 +--
 net/atm/mpc.c          |  3 +--
 net/atm/pppoatm.c      |  3 +--
 net/atm/raw.c          |  4 ++--
 8 files changed, 23 insertions(+), 14 deletions(-)

diff --git a/include/linux/atmdev.h b/include/linux/atmdev.h
index 0c27515d2cf6..8124815eb121 100644
--- a/include/linux/atmdev.h
+++ b/include/linux/atmdev.h
@@ -214,6 +214,7 @@ struct atmphy_ops {
 struct atm_skb_data {
 	struct atm_vcc	*vcc;		/* ATM VCC */
 	unsigned long	atm_options;	/* ATM layer options */
+	unsigned int	acct_truesize;  /* truesize accounted to vcc */
 };
 
 #define VCC_HTABLE_SIZE 32
@@ -241,6 +242,20 @@ void vcc_insert_socket(struct sock *sk);
 
 void atm_dev_release_vccs(struct atm_dev *dev);
 
+static inline void atm_account_tx(struct atm_vcc *vcc, struct sk_buff *skb)
+{
+	/*
+	 * Because ATM skbs may not belong to a sock (and we don't
+	 * necessarily want to), skb->truesize may be adjusted,
+	 * escaping the hack in pskb_expand_head() which avoids
+	 * doing so for some cases. So stash the value of truesize
+	 * at the time we accounted it, and atm_pop_raw() can use
+	 * that value later, in case it changes.
+	 */
+	refcount_add(skb->truesize, &sk_atm(vcc)->sk_wmem_alloc);
+	ATM_SKB(skb)->acct_truesize = skb->truesize;
+	ATM_SKB(skb)->atm_options = vcc->atm_options;
+}
 
 static inline void atm_force_charge(struct atm_vcc *vcc,int truesize)
 {
diff --git a/net/atm/br2684.c b/net/atm/br2684.c
index 4e111196f902..bc21f8e8daf2 100644
--- a/net/atm/br2684.c
+++ b/net/atm/br2684.c
@@ -252,8 +252,7 @@ static int br2684_xmit_vcc(struct sk_buff *skb, struct net_device *dev,
 
 	ATM_SKB(skb)->vcc = atmvcc = brvcc->atmvcc;
 	pr_debug("atm_skb(%p)->vcc(%p)->dev(%p)\n", skb, atmvcc, atmvcc->dev);
-	refcount_add(skb->truesize, &sk_atm(atmvcc)->sk_wmem_alloc);
-	ATM_SKB(skb)->atm_options = atmvcc->atm_options;
+	atm_account_tx(atmvcc, skb);
 	dev->stats.tx_packets++;
 	dev->stats.tx_bytes += skb->len;
 
diff --git a/net/atm/clip.c b/net/atm/clip.c
index 65f706e4344c..60920a42f640 100644
--- a/net/atm/clip.c
+++ b/net/atm/clip.c
@@ -381,8 +381,7 @@ static netdev_tx_t clip_start_xmit(struct sk_buff *skb,
 		memcpy(here, llc_oui, sizeof(llc_oui));
 		((__be16 *) here)[3] = skb->protocol;
 	}
-	refcount_add(skb->truesize, &sk_atm(vcc)->sk_wmem_alloc);
-	ATM_SKB(skb)->atm_options = vcc->atm_options;
+	atm_account_tx(vcc, skb);
 	entry->vccs->last_use = jiffies;
 	pr_debug("atm_skb(%p)->vcc(%p)->dev(%p)\n", skb, vcc, vcc->dev);
 	old = xchg(&entry->vccs->xoff, 1);	/* assume XOFF ... */
diff --git a/net/atm/common.c b/net/atm/common.c
index 8a4f99114cd2..9e812c782a37 100644
--- a/net/atm/common.c
+++ b/net/atm/common.c
@@ -630,10 +630,9 @@ int vcc_sendmsg(struct socket *sock, struct msghdr *m, size_t size)
 		goto out;
 	}
 	pr_debug("%d += %d\n", sk_wmem_alloc_get(sk), skb->truesize);
-	refcount_add(skb->truesize, &sk->sk_wmem_alloc);
+	atm_account_tx(vcc, skb);
 
 	skb->dev = NULL; /* for paths shared with net_device interfaces */
-	ATM_SKB(skb)->atm_options = vcc->atm_options;
 	if (!copy_from_iter_full(skb_put(skb, size), size, &m->msg_iter)) {
 		kfree_skb(skb);
 		error = -EFAULT;
diff --git a/net/atm/lec.c b/net/atm/lec.c
index a3d93a1bb133..d7cc165e24e0 100644
--- a/net/atm/lec.c
+++ b/net/atm/lec.c
@@ -179,9 +179,8 @@ lec_send(struct atm_vcc *vcc, struct sk_buff *skb)
 	struct net_device *dev = skb->dev;
 
 	ATM_SKB(skb)->vcc = vcc;
-	ATM_SKB(skb)->atm_options = vcc->atm_options;
+	atm_account_tx(vcc, skb);
 
-	refcount_add(skb->truesize, &sk_atm(vcc)->sk_wmem_alloc);
 	if (vcc->send(vcc, skb) < 0) {
 		dev->stats.tx_dropped++;
 		return;
diff --git a/net/atm/mpc.c b/net/atm/mpc.c
index 5677147209e8..db9a1838687c 100644
--- a/net/atm/mpc.c
+++ b/net/atm/mpc.c
@@ -555,8 +555,7 @@ static int send_via_shortcut(struct sk_buff *skb, struct mpoa_client *mpc)
 					sizeof(struct llc_snap_hdr));
 	}
 
-	refcount_add(skb->truesize, &sk_atm(entry->shortcut)->sk_wmem_alloc);
-	ATM_SKB(skb)->atm_options = entry->shortcut->atm_options;
+	atm_account_tx(entry->shortcut, skb);
 	entry->shortcut->send(entry->shortcut, skb);
 	entry->packets_fwded++;
 	mpc->in_ops->put(entry);
diff --git a/net/atm/pppoatm.c b/net/atm/pppoatm.c
index 21d9d341a619..af8c4b38b746 100644
--- a/net/atm/pppoatm.c
+++ b/net/atm/pppoatm.c
@@ -350,8 +350,7 @@ static int pppoatm_send(struct ppp_channel *chan, struct sk_buff *skb)
 		return 1;
 	}
 
-	refcount_add(skb->truesize, &sk_atm(ATM_SKB(skb)->vcc)->sk_wmem_alloc);
-	ATM_SKB(skb)->atm_options = ATM_SKB(skb)->vcc->atm_options;
+	atm_account_tx(vcc, skb);
 	pr_debug("atm_skb(%p)->vcc(%p)->dev(%p)\n",
 		 skb, ATM_SKB(skb)->vcc, ATM_SKB(skb)->vcc->dev);
 	ret = ATM_SKB(skb)->vcc->send(ATM_SKB(skb)->vcc, skb)
diff --git a/net/atm/raw.c b/net/atm/raw.c
index ee10e8d46185..b3ba44aab0ee 100644
--- a/net/atm/raw.c
+++ b/net/atm/raw.c
@@ -35,8 +35,8 @@ static void atm_pop_raw(struct atm_vcc *vcc, struct sk_buff *skb)
 	struct sock *sk = sk_atm(vcc);
 
 	pr_debug("(%d) %d -= %d\n",
-		 vcc->vci, sk_wmem_alloc_get(sk), skb->truesize);
-	WARN_ON(refcount_sub_and_test(skb->truesize, &sk->sk_wmem_alloc));
+		 vcc->vci, sk_wmem_alloc_get(sk), ATM_SKB(skb)->acct_truesize);
+	WARN_ON(refcount_sub_and_test(ATM_SKB(skb)->acct_truesize, &sk->sk_wmem_alloc));
 	dev_kfree_skb_any(skb);
 	sk->sk_write_space(sk);
 }
-- 
2.17.0

-- 
dwmw2