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Subject[PATCH 01/12] netvm: Prevent a stream-specific deadlock
Date
It could happen that all !SOCK_MEMALLOC sockets have buffered so
much data that we're over the global rmem limit. This will prevent
SOCK_MEMALLOC buffers from receiving data, which will prevent userspace
from running, which is needed to reduce the buffered data.

Fix this by exempting the SOCK_MEMALLOC sockets from the rmem limit.
Once this change it applied, it is important that sockets that set
SOCK_MEMALLOC do not clear the flag until the socket is being torn down.
If this happens, a warning is generated and the tokens reclaimed to
avoid accounting errors until the bug is fixed.

[davem@davemloft.net: Warning about clearing SOCK_MEMALLOC]
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Mel Gorman <mgorman@suse.de>
---
include/net/sock.h | 7 ++++---
net/caif/caif_socket.c | 2 +-
net/core/sock.c | 14 +++++++++++++-
net/ipv4/tcp_input.c | 12 ++++++------
net/sctp/ulpevent.c | 2 +-
5 files changed, 25 insertions(+), 12 deletions(-)
diff --git a/include/net/sock.h b/include/net/sock.h
index 7cb714c..eb0dd76 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -1280,12 +1280,13 @@ static inline int sk_wmem_schedule(struct sock *sk, int size)
__sk_mem_schedule(sk, size, SK_MEM_SEND);
}

-static inline int sk_rmem_schedule(struct sock *sk, int size)
+static inline int sk_rmem_schedule(struct sock *sk, struct sk_buff *skb)
{
if (!sk_has_account(sk))
return 1;
- return size <= sk->sk_forward_alloc ||
- __sk_mem_schedule(sk, size, SK_MEM_RECV);
+ return skb->truesize <= sk->sk_forward_alloc ||
+ __sk_mem_schedule(sk, skb->truesize, SK_MEM_RECV) ||
+ skb_pfmemalloc(skb);
}

static inline void sk_mem_reclaim(struct sock *sk)
diff --git a/net/caif/caif_socket.c b/net/caif/caif_socket.c
index 5016fa5..aaf711c 100644
--- a/net/caif/caif_socket.c
+++ b/net/caif/caif_socket.c
@@ -142,7 +142,7 @@ static int caif_queue_rcv_skb(struct sock *sk, struct sk_buff *skb)
err = sk_filter(sk, skb);
if (err)
return err;
- if (!sk_rmem_schedule(sk, skb->truesize) && rx_flow_is_on(cf_sk)) {
+ if (!sk_rmem_schedule(sk, skb) && rx_flow_is_on(cf_sk)) {
set_rx_flow_off(cf_sk);
if (net_ratelimit())
pr_debug("sending flow OFF due to rmem_schedule\n");
diff --git a/net/core/sock.c b/net/core/sock.c
index 906f6f4..e3dea27 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -289,6 +289,18 @@ void sk_clear_memalloc(struct sock *sk)
sock_reset_flag(sk, SOCK_MEMALLOC);
sk->sk_allocation &= ~__GFP_MEMALLOC;
static_key_slow_dec(&memalloc_socks);
+
+ /*
+ * SOCK_MEMALLOC is allowed to ignore rmem limits to ensure forward
+ * progress of swapping. However, if SOCK_MEMALLOC is cleared while
+ * it has rmem allocations there is a risk that the user of the
+ * socket cannot make forward progress due to exceeding the rmem
+ * limits. By rights, sk_clear_memalloc() should only be called
+ * on sockets being torn down but warn and reset the accounting if
+ * that assumption breaks.
+ */
+ if (WARN_ON(sk->sk_forward_alloc))
+ sk_mem_reclaim(sk);
}
EXPORT_SYMBOL_GPL(sk_clear_memalloc);

@@ -391,7 +403,7 @@ int sock_queue_rcv_skb(struct sock *sk, struct sk_buff *skb)
if (err)
return err;

- if (!sk_rmem_schedule(sk, skb->truesize)) {
+ if (!sk_rmem_schedule(sk, skb)) {
atomic_inc(&sk->sk_drops);
return -ENOBUFS;
}
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 257b617..b1c787c 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -4434,19 +4434,19 @@ static void tcp_ofo_queue(struct sock *sk)
static int tcp_prune_ofo_queue(struct sock *sk);
static int tcp_prune_queue(struct sock *sk);

-static inline int tcp_try_rmem_schedule(struct sock *sk, unsigned int size)
+static inline int tcp_try_rmem_schedule(struct sock *sk, struct sk_buff *skb)
{
if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf ||
- !sk_rmem_schedule(sk, size)) {
+ !sk_rmem_schedule(sk, skb)) {

if (tcp_prune_queue(sk) < 0)
return -1;

- if (!sk_rmem_schedule(sk, size)) {
+ if (!sk_rmem_schedule(sk, skb)) {
if (!tcp_prune_ofo_queue(sk))
return -1;

- if (!sk_rmem_schedule(sk, size))
+ if (!sk_rmem_schedule(sk, skb))
return -1;
}
}
@@ -4461,7 +4461,7 @@ static void tcp_data_queue_ofo(struct sock *sk, struct sk_buff *skb)

TCP_ECN_check_ce(tp, skb);

- if (tcp_try_rmem_schedule(sk, skb->truesize)) {
+ if (tcp_try_rmem_schedule(sk, skb)) {
/* TODO: should increment a counter */
__kfree_skb(skb);
return;
@@ -4630,7 +4630,7 @@ static void tcp_data_queue(struct sock *sk, struct sk_buff *skb)
if (eaten <= 0) {
queue_and_out:
if (eaten < 0 &&
- tcp_try_rmem_schedule(sk, skb->truesize))
+ tcp_try_rmem_schedule(sk, skb))
goto drop;

skb_set_owner_r(skb, sk);
diff --git a/net/sctp/ulpevent.c b/net/sctp/ulpevent.c
index 8a84017..6c6ed2d 100644
--- a/net/sctp/ulpevent.c
+++ b/net/sctp/ulpevent.c
@@ -702,7 +702,7 @@ struct sctp_ulpevent *sctp_ulpevent_make_rcvmsg(struct sctp_association *asoc,
if (rx_count >= asoc->base.sk->sk_rcvbuf) {

if ((asoc->base.sk->sk_userlocks & SOCK_RCVBUF_LOCK) ||
- (!sk_rmem_schedule(asoc->base.sk, chunk->skb->truesize)))
+ (!sk_rmem_schedule(asoc->base.sk, chunk->skb)))
goto fail;
}

--
1.7.9.2


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