xfrm: ipcomp: remove unnecessary get_cpu()

While testing ipcomp on a realtime kernel, Xiumei reported a "sleeping
in atomic" bug, caused by a memory allocation while preemption is
disabled (ipcomp_decompress -> alloc_page -> ... get_page_from_freelist).

As Sebastian noted [1], this get_cpu() isn't actually needed, since
ipcomp_decompress() is called in napi context anyway, so BH is already
disabled.

This patch replaces get_cpu + per_cpu_ptr with this_cpu_ptr, then
simplifies the error returns, since there isn't any common operation
left.

[1] https://lore.kernel.org/lkml/20190820082810.ixkmi56fp7u7eyn2@linutronix.de/

Cc: Juri Lelli <jlelli@redhat.com>
Reported-by: Xiumei Mu <xmu@redhat.com>
Suggested-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

diff --git a/net/xfrm/xfrm_ipcomp.c b/net/xfrm/xfrm_ipcomp.c
index 4d422447aadc363c2551d98c51532a2f5270c9d6..2e8afe078d6129143c4572a8d2bba02c822a2fc1 100644 (file)
--- a/net/xfrm/xfrm_ipcomp.c
+++ b/net/xfrm/xfrm_ipcomp.c
@@ -41,19 +41,16 @@ static int ipcomp_decompress(struct xfrm_state *x, struct sk_buff *skb)
        const int plen = skb->len;
        int dlen = IPCOMP_SCRATCH_SIZE;
        const u8 *start = skb->data;
-       const int cpu = get_cpu();
-       u8 *scratch = *per_cpu_ptr(ipcomp_scratches, cpu);
-       struct crypto_comp *tfm = *per_cpu_ptr(ipcd->tfms, cpu);
+       u8 *scratch = *this_cpu_ptr(ipcomp_scratches);
+       struct crypto_comp *tfm = *this_cpu_ptr(ipcd->tfms);
        int err = crypto_comp_decompress(tfm, start, plen, scratch, &dlen);
        int len;
 
        if (err)
-               goto out;
+               return err;
 
-       if (dlen < (plen + sizeof(struct ip_comp_hdr))) {
-               err = -EINVAL;
-               goto out;
-       }
+       if (dlen < (plen + sizeof(struct ip_comp_hdr)))
+               return -EINVAL;
 
        len = dlen - plen;
        if (len > skb_tailroom(skb))
@@ -68,16 +65,14 @@ static int ipcomp_decompress(struct xfrm_state *x, struct sk_buff *skb)
                skb_frag_t *frag;
                struct page *page;
 
-               err = -EMSGSIZE;
                if (WARN_ON(skb_shinfo(skb)->nr_frags >= MAX_SKB_FRAGS))
-                       goto out;
+                       return -EMSGSIZE;
 
                frag = skb_shinfo(skb)->frags + skb_shinfo(skb)->nr_frags;
                page = alloc_page(GFP_ATOMIC);
 
-               err = -ENOMEM;
                if (!page)
-                       goto out;
+                       return -ENOMEM;
 
                __skb_frag_set_page(frag, page);
 
@@ -96,11 +91,7 @@ static int ipcomp_decompress(struct xfrm_state *x, struct sk_buff *skb)
                skb_shinfo(skb)->nr_frags++;
        }
 
-       err = 0;
-
-out:
-       put_cpu();
-       return err;
+       return 0;
 }
 
 int ipcomp_input(struct xfrm_state *x, struct sk_buff *skb)