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authorEric Dumazet <edumazet@google.com>2019-10-23 22:44:48 -0700
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2019-11-10 11:34:43 +0100
commitc7dba6a99aec3956f5c5b2c6a4cd1bf5fdc36a5e (patch)
treea515fc37b2fb179aca385de4d669fd8b9fce4f6c
parent71e92518a9cea75a2e0d6dd8d74684bce9e4b231 (diff)
net: add skb_queue_empty_lockless()
[ Upstream commit d7d16a89350ab263484c0aa2b523dd3a234e4a80 ] Some paths call skb_queue_empty() without holding the queue lock. We must use a barrier in order to not let the compiler do strange things, and avoid KCSAN splats. Adding a barrier in skb_queue_empty() might be overkill, I prefer adding a new helper to clearly identify points where the callers might be lockless. This might help us finding real bugs. The corresponding WRITE_ONCE() should add zero cost for current compilers. Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--include/linux/skbuff.h33
1 files changed, 24 insertions, 9 deletions
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 9b18d33681c2..39a7cecaa880 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -1501,6 +1501,19 @@ static inline int skb_queue_empty(const struct sk_buff_head *list)
}
/**
+ * skb_queue_empty_lockless - check if a queue is empty
+ * @list: queue head
+ *
+ * Returns true if the queue is empty, false otherwise.
+ * This variant can be used in lockless contexts.
+ */
+static inline bool skb_queue_empty_lockless(const struct sk_buff_head *list)
+{
+ return READ_ONCE(list->next) == (const struct sk_buff *) list;
+}
+
+
+/**
* skb_queue_is_last - check if skb is the last entry in the queue
* @list: queue head
* @skb: buffer
@@ -1853,9 +1866,11 @@ static inline void __skb_insert(struct sk_buff *newsk,
struct sk_buff *prev, struct sk_buff *next,
struct sk_buff_head *list)
{
- newsk->next = next;
- newsk->prev = prev;
- next->prev = prev->next = newsk;
+ /* see skb_queue_empty_lockless() for the opposite READ_ONCE() */
+ WRITE_ONCE(newsk->next, next);
+ WRITE_ONCE(newsk->prev, prev);
+ WRITE_ONCE(next->prev, newsk);
+ WRITE_ONCE(prev->next, newsk);
list->qlen++;
}
@@ -1866,11 +1881,11 @@ static inline void __skb_queue_splice(const struct sk_buff_head *list,
struct sk_buff *first = list->next;
struct sk_buff *last = list->prev;
- first->prev = prev;
- prev->next = first;
+ WRITE_ONCE(first->prev, prev);
+ WRITE_ONCE(prev->next, first);
- last->next = next;
- next->prev = last;
+ WRITE_ONCE(last->next, next);
+ WRITE_ONCE(next->prev, last);
}
/**
@@ -2011,8 +2026,8 @@ static inline void __skb_unlink(struct sk_buff *skb, struct sk_buff_head *list)
next = skb->next;
prev = skb->prev;
skb->next = skb->prev = NULL;
- next->prev = prev;
- prev->next = next;
+ WRITE_ONCE(next->prev, prev);
+ WRITE_ONCE(prev->next, next);
}
/**