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net: do not leave an empty skb in write queue
Under memory stress conditions, tcp_sendmsg_locked()
might call sk_stream_wait_memory(), thus releasing the socket lock.
If a fresh skb has been allocated prior to this,
we should not leave it in the write queue otherwise
tcp_write_xmit() could panic.
This apparently does not happen often, but a future change
in __sk_mem_raise_allocated() that Shakeel and others are
considering would increase chances of being hurt.
Under discussion is to remove this controversial part:
/* Fail only if socket is _under_ its sndbuf.
* In this case we cannot block, so that we have to fail.
*/
if (sk->sk_wmem_queued + size >= sk->sk_sndbuf) {
/* Force charge with __GFP_NOFAIL */
if (memcg_charge && !charged) {
mem_cgroup_charge_skmem(sk->sk_memcg, amt,
gfp_memcg_charge() | __GFP_NOFAIL);
}
return 1;
}
Fixes: fdfc5c8594
("tcp: remove empty skb from write queue in error cases")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Link: https://lore.kernel.org/r/20231019112457.1190114-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
parent
8c0b48e01d
commit
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@ -927,10 +927,11 @@ int tcp_send_mss(struct sock *sk, int *size_goal, int flags)
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return mss_now;
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}
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/* In some cases, both sendmsg() could have added an skb to the write queue,
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* but failed adding payload on it. We need to remove it to consume less
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/* In some cases, sendmsg() could have added an skb to the write queue,
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* but failed adding payload on it. We need to remove it to consume less
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* memory, but more importantly be able to generate EPOLLOUT for Edge Trigger
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* epoll() users.
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* epoll() users. Another reason is that tcp_write_xmit() does not like
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* finding an empty skb in the write queue.
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*/
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void tcp_remove_empty_skb(struct sock *sk)
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{
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@ -1289,6 +1290,7 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size)
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wait_for_space:
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set_bit(SOCK_NOSPACE, &sk->sk_socket->flags);
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tcp_remove_empty_skb(sk);
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if (copied)
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tcp_push(sk, flags & ~MSG_MORE, mss_now,
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TCP_NAGLE_PUSH, size_goal);
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