path: root/include/net/sock.h
diff options
authorDeepa Dinamani <deepa.kernel@gmail.com>2018-12-27 18:55:09 -0800
committerDavid S. Miller <davem@davemloft.net>2019-01-01 09:47:59 -0800
commit3a0ed3e9619738067214871e9cb826fa23b2ddb9 (patch)
treef27788a1eb07823c642631cb4d27aa0c052e3095 /include/net/sock.h
parentibmveth: fix DMA unmap error in ibmveth_xmit_start error path (diff)
sock: Make sock->sk_stamp thread-safe
Al Viro mentioned (Message-ID <20170626041334.GZ10672@ZenIV.linux.org.uk>) that there is probably a race condition lurking in accesses of sk_stamp on 32-bit machines. sock->sk_stamp is of type ktime_t which is always an s64. On a 32 bit architecture, we might run into situations of unsafe access as the access to the field becomes non atomic. Use seqlocks for synchronization. This allows us to avoid using spinlocks for readers as readers do not need mutual exclusion. Another approach to solve this is to require sk_lock for all modifications of the timestamps. The current approach allows for timestamps to have their own lock: sk_stamp_lock. This allows for the patch to not compete with already existing critical sections, and side effects are limited to the paths in the patch. The addition of the new field maintains the data locality optimizations from commit 9115e8cd2a0c ("net: reorganize struct sock for better data locality") Note that all the instances of the sk_stamp accesses are either through the ioctl or the syscall recvmsg. Signed-off-by: Deepa Dinamani <deepa.kernel@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'include/net/sock.h')
1 files changed, 35 insertions, 3 deletions
diff --git a/include/net/sock.h b/include/net/sock.h
index a6235c286ef9..2b229f7be8eb 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -298,6 +298,7 @@ struct sock_common {
* @sk_filter: socket filtering instructions
* @sk_timer: sock cleanup timer
* @sk_stamp: time stamp of last packet received
+ * @sk_stamp_seq: lock for accessing sk_stamp on 32 bit architectures only
* @sk_tsflags: SO_TIMESTAMPING socket options
* @sk_tskey: counter to disambiguate concurrent tstamp requests
* @sk_zckey: counter to order MSG_ZEROCOPY notifications
@@ -474,6 +475,9 @@ struct sock {
const struct cred *sk_peer_cred;
long sk_rcvtimeo;
ktime_t sk_stamp;
+#if BITS_PER_LONG==32
+ seqlock_t sk_stamp_seq;
u16 sk_tsflags;
u8 sk_shutdown;
u32 sk_tskey;
@@ -2297,6 +2301,34 @@ static inline void sk_drops_add(struct sock *sk, const struct sk_buff *skb)
atomic_add(segs, &sk->sk_drops);
+static inline ktime_t sock_read_timestamp(struct sock *sk)
+#if BITS_PER_LONG==32
+ unsigned int seq;
+ ktime_t kt;
+ do {
+ seq = read_seqbegin(&sk->sk_stamp_seq);
+ kt = sk->sk_stamp;
+ } while (read_seqretry(&sk->sk_stamp_seq, seq));
+ return kt;
+ return sk->sk_stamp;
+static inline void sock_write_timestamp(struct sock *sk, ktime_t kt)
+#if BITS_PER_LONG==32
+ write_seqlock(&sk->sk_stamp_seq);
+ sk->sk_stamp = kt;
+ write_sequnlock(&sk->sk_stamp_seq);
+ sk->sk_stamp = kt;
void __sock_recv_timestamp(struct msghdr *msg, struct sock *sk,
struct sk_buff *skb);
void __sock_recv_wifi_status(struct msghdr *msg, struct sock *sk,
@@ -2321,7 +2353,7 @@ sock_recv_timestamp(struct msghdr *msg, struct sock *sk, struct sk_buff *skb)
__sock_recv_timestamp(msg, sk, skb);
- sk->sk_stamp = kt;
+ sock_write_timestamp(sk, kt);
if (sock_flag(sk, SOCK_WIFI_STATUS) && skb->wifi_acked_valid)
__sock_recv_wifi_status(msg, sk, skb);
@@ -2342,9 +2374,9 @@ static inline void sock_recv_ts_and_drops(struct msghdr *msg, struct sock *sk,
if (sk->sk_flags & FLAGS_TS_OR_DROPS || sk->sk_tsflags & TSFLAGS_ANY)
__sock_recv_ts_and_drops(msg, sk, skb);
else if (unlikely(sock_flag(sk, SOCK_TIMESTAMP)))
- sk->sk_stamp = skb->tstamp;
+ sock_write_timestamp(sk, skb->tstamp);
else if (unlikely(sk->sk_stamp == SK_DEFAULT_STAMP))
- sk->sk_stamp = 0;
+ sock_write_timestamp(sk, 0);
void __sock_tx_timestamp(__u16 tsflags, __u8 *tx_flags);