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tcp: fix possible deadlock in tcp_send_fin() 

Using sk_stream_alloc_skb() in tcp_send_fin() is dangerous in
case a huge process is killed by OOM, and tcp_mem[2] is hit.

To be able to free memory we need to make progress, so this
patch allows FIN packets to not care about tcp_mem[2], if
skb allocation succeeded.

In a follow-up patch, we might abort tcp_send_fin() infinite loop
in case TIF_MEMDIE is set on this thread, as memory allocator
did its best getting extra memory already.

This patch reverts d22e153718 ("tcp: fix tcp fin memory accounting")

Fixes: d22e153718 ("tcp: fix tcp fin memory accounting")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2015-04-21 18:32:24 -07:00 committed by David S. Miller
parent 5e6c94a999
commit d83769a580
1 changed files with 19 additions and 1 deletions
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20
net/ipv4/tcp_output.c
View File

@ -2812,6 +2812,21 @@ begin_fwd:
}
}
/* We allow to exceed memory limits for FIN packets to expedite
* connection tear down and (memory) recovery.
* Otherwise tcp_send_fin() could loop forever.
*/
static void sk_forced_wmem_schedule(struct sock *sk, int size)
{
int amt, status;
if (size <= sk->sk_forward_alloc)
return;
amt = sk_mem_pages(size);
sk->sk_forward_alloc += amt * SK_MEM_QUANTUM;
sk_memory_allocated_add(sk, amt, &status);
}
/* Send a fin. The caller locks the socket for us. This cannot be
* allowed to fail queueing a FIN frame under any circumstances.
*/
@ -2834,11 +2849,14 @@ void tcp_send_fin(struct sock *sk)
} else {
/* Socket is locked, keep trying until memory is available. */
for (;;) {
skb = sk_stream_alloc_skb(sk, 0, sk->sk_allocation);
skb = alloc_skb_fclone(MAX_TCP_HEADER,
sk->sk_allocation);
if (skb)
break;
yield();
}
skb_reserve(skb, MAX_TCP_HEADER);
sk_forced_wmem_schedule(sk, skb->truesize);
/* FIN eats a sequence byte, write_seq advanced by tcp_queue_skb(). */
tcp_init_nondata_skb(skb, tp->write_seq,
TCPHDR_ACK | TCPHDR_FIN);