On Fri, Apr 01, 2016 at 12:47:24PM -0700, santosh shilimkar wrote: > (cc-ing netdev) > On 3/30/2016 7:59 PM, Wengang Wang wrote: > > > > > >在 2016年03月31日 09:51, Wengang Wang 写道: > >> > >> > >>在 2016年03月31日 01:16, santosh shilimkar 写道: > >>>Hi Wengang, > >>> > >>>On 3/30/2016 9:19 AM, Leon Romanovsky wrote: > >>>>On Wed, Mar 30, 2016 at 05:08:22PM +0800, Wengang Wang wrote: > >>>>>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. > >>>>> > > > >To be more detailed. Here, the two paths (user calls recvmsg and > >hardware receives data) are for different rds socks. thus the > >rds_sock->rs_recv_lock is not helpful to sync the updating on congestion > >map. > > > For archive purpose, let me try to conclude the thread. I synced > with Wengang offlist and came up with below fix. I was under > impression that __set_bit_le() was atmoic version. After fixing > it like patch(end of the email), the bug gets addressed. > > I will probably send this as fix for stable as well. > > > From 5614b61f6fdcd6ae0c04e50b97efd13201762294 Mon Sep 17 00:00:00 2001 > From: Santosh Shilimkar <santosh.shilim...@oracle.com> > Date: Wed, 30 Mar 2016 23:26:47 -0700 > Subject: [PATCH] RDS: Fix the atomicity for congestion map update > > Two different threads with different rds sockets may be in > rds_recv_rcvbuf_delta() via receive path. If their ports > both map to the same word in the congestion map, then > using non-atomic ops to update it could cause the map to > be incorrect. Lets use atomics to avoid such an issue. > > Full credit to Wengang <wen.gang.w...@oracle.com> for > finding the issue, analysing it and also pointing out > to offending code with spin lock based fix.
I'm glad that you solved the issue without spinlocks. Out of curiosity, I see that this patch is needed to be sent to Dave and applied by him. Is it right? ➜ linus-tree git:(master) ./scripts/get_maintainer.pl -f net/rds/cong.c Santosh Shilimkar <santosh.shilim...@oracle.com> (supporter:RDS - RELIABLE DATAGRAM SOCKETS) "David S. Miller" <da...@davemloft.net> (maintainer:NETWORKING [GENERAL]) netdev@vger.kernel.org (open list:RDS - RELIABLE DATAGRAM SOCKETS) linux-r...@vger.kernel.org (open list:RDS - RELIABLE DATAGRAM SOCKETS) rds-de...@oss.oracle.com (moderated list:RDS - RELIABLE DATAGRAM SOCKETS) linux-ker...@vger.kernel.org (open list) > > Signed-off-by: Wengang Wang <wen.gang.w...@oracle.com> > Signed-off-by: Santosh Shilimkar <santosh.shilim...@oracle.com> Reviewed-by: Leon Romanovsky <l...@leon.nu>
