Hi Leon,

在 2016年03月31日 00:19, Leon Romanovsky 写道:

On Wed, Mar 30, 2016 at 05:08:22PM +0800, Wengang Wang wrote:

quoted

Problem is found that some among a lot of parallel RDS communications hang.
In my test ten or so among 33 communications hang. The send requests got
-ENOBUF error meaning the peer socket (port) is congested. But meanwhile,
peer socket (port) is not congested.

The congestion map updating can happen in two paths: one is in rds_recvmsg path
and the other is when it receives packets from the hardware. There is no
synchronization when updating the congestion map. So a bit operation (clearing)
in the rds_recvmsg path can be skipped by another bit operation (setting) in
hardware packet receving path.

Fix is to add a spin lock per congestion map to sync the update on it.
No performance drop found during the test for the fix.

I assume that this change fixed your issue, however it looks suspicious
that performance wasn't change.

Sure it I verified that patch fixes the issue.
For performance, I will reply to Santosh's email later, please check there.

quoted

Signed-off-by: Wengang Wang <redacted>
---
  net/rds/cong.c | 7 +++++++
  net/rds/rds.h  | 1 +
  2 files changed, 8 insertions(+)

According to get_maintainer script, you send this patch to wrong lists
and persons.

➜  linux git:(master) ./scripts/get_maintainer.pl -f net/rds/cong.c
Santosh Shilimkar [off-list ref] (supporter:RDS - RELIABLE DATAGRAM SOCKETS)
"David S. Miller" [off-list ref] (maintainer:NETWORKING [GENERAL])
netdev-u79uwXL29TY76Z2rM5mHXA@public.gmane.org (open list:RDS - RELIABLE DATAGRAM SOCKETS)
linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org (open list:RDS - RELIABLE DATAGRAM SOCKETS)

So linux-rdma is here :)

thanks,
wengang

rds-devel-N0ozoZBvEnrZJqsBc5GL+g@public.gmane.org (moderated list:RDS - RELIABLE DATAGRAM SOCKETS)
linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org (open list)

quoted

diff --git a/net/rds/cong.c b/net/rds/cong.c
index e6144b8..7afc1bf 100644
--- a/net/rds/cong.c
+++ b/net/rds/cong.c

@@ -144,6 +144,7 @@ static struct rds_cong_map *rds_cong_from_addr(__be32 addr)
  	if (!map)
  		return NULL;
  
+	spin_lock_init(&map->m_lock);
  	map->m_addr = addr;
  	init_waitqueue_head(&map->m_waitq);
  	INIT_LIST_HEAD(&map->m_conn_list);

@@ -292,6 +293,7 @@ void rds_cong_set_bit(struct rds_cong_map *map, __be16 port)
  {
  	unsigned long i;
  	unsigned long off;
+	unsigned long flags;
  
  	rdsdebug("setting congestion for %pI4:%u in map %p\n",
  	  &map->m_addr, ntohs(port), map);

@@ -299,13 +301,16 @@ void rds_cong_set_bit(struct rds_cong_map *map, __be16 port)
  	i = be16_to_cpu(port) / RDS_CONG_MAP_PAGE_BITS;
  	off = be16_to_cpu(port) % RDS_CONG_MAP_PAGE_BITS;
  
+	spin_lock_irqsave(&map->m_lock, flags);
  	__set_bit_le(off, (void *)map->m_page_addrs[i]);
+	spin_unlock_irqrestore(&map->m_lock, flags);
  }
  
  void rds_cong_clear_bit(struct rds_cong_map *map, __be16 port)
  {
  	unsigned long i;
  	unsigned long off;
+	unsigned long flags;
  
  	rdsdebug("clearing congestion for %pI4:%u in map %p\n",
  	  &map->m_addr, ntohs(port), map);

@@ -313,7 +318,9 @@ void rds_cong_clear_bit(struct rds_cong_map *map, __be16 port)
  	i = be16_to_cpu(port) / RDS_CONG_MAP_PAGE_BITS;
  	off = be16_to_cpu(port) % RDS_CONG_MAP_PAGE_BITS;
  
+	spin_lock_irqsave(&map->m_lock, flags);
  	__clear_bit_le(off, (void *)map->m_page_addrs[i]);
+	spin_unlock_irqrestore(&map->m_lock, flags);
  }
  
  static int rds_cong_test_bit(struct rds_cong_map *map, __be16 port)

diff --git a/net/rds/rds.h b/net/rds/rds.h
index 80256b0..f359cf8 100644
--- a/net/rds/rds.h
+++ b/net/rds/rds.h

@@ -59,6 +59,7 @@ struct rds_cong_map {
  	__be32			m_addr;
  	wait_queue_head_t	m_waitq;
  	struct list_head	m_conn_list;
+	spinlock_t		m_lock;
  	unsigned long		m_page_addrs[RDS_CONG_MAP_PAGES];
  };
  

-- 
2.1.0

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