Commit e7820e39 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller

net: Revert "net: avoid one atomic operation in skb_clone()"

Not sure what I was thinking, but doing anything after
releasing a refcount is suicidal or/and embarrassing.

By the time we set skb->fclone to SKB_FCLONE_FREE, another cpu
could have released last reference and freed whole skb.

We potentially corrupt memory or trap if CONFIG_DEBUG_PAGEALLOC is set.
Reported-by: default avatarChris Mason <>
Fixes: ce1a4ea3 ("net: avoid one atomic operation in skb_clone()")
Signed-off-by: default avatarEric Dumazet <>
Cc: Sabrina Dubroca <>
Signed-off-by: default avatarDavid S. Miller <>
parent 892d6eb1
......@@ -552,20 +552,13 @@ static void kfree_skbmem(struct sk_buff *skb)
fclones = container_of(skb, struct sk_buff_fclones, skb2);
/* Warning : We must perform the atomic_dec_and_test() before
* setting skb->fclone back to SKB_FCLONE_FREE, otherwise
* skb_clone() could set clone_ref to 2 before our decrement.
* Anyway, if we are going to free the structure, no need to
* rewrite skb->fclone.
/* The clone portion is available for
* fast-cloning again.
if (atomic_dec_and_test(&fclones->fclone_ref)) {
skb->fclone = SKB_FCLONE_FREE;
if (atomic_dec_and_test(&fclones->fclone_ref))
kmem_cache_free(skbuff_fclone_cache, fclones);
} else {
/* The clone portion is available for
* fast-cloning again.
skb->fclone = SKB_FCLONE_FREE;
......@@ -887,11 +880,7 @@ struct sk_buff *skb_clone(struct sk_buff *skb, gfp_t gfp_mask)
if (skb->fclone == SKB_FCLONE_ORIG &&
n->fclone == SKB_FCLONE_FREE) {
n->fclone = SKB_FCLONE_CLONE;
/* As our fastclone was free, clone_ref must be 1 at this point.
* We could use atomic_inc() here, but it is faster
* to set the final value.
atomic_set(&fclones->fclone_ref, 2);
} else {
if (skb_pfmemalloc(skb))
gfp_mask |= __GFP_MEMALLOC;
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