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SubjectRe: [PATCHv2] rds: rds_cong_queue_updates needs to defer the congestion update transmission
From: Sowmini Varadhan <>
Date: Tue, 10 Feb 2015 13:33:37 -0500

> When the RDS transport is TCP, we cannot inline the call to rds_send_xmit
> from rds_cong_queue_update because
> (a) we are already holding the sock_lock in the recv path, and
> will deadlock when tcp_setsockopt/tcp_sendmsg try to get the sock
> lock
> (b) cong_queue_update does an irqsave on the rds_cong_lock, and this
> will trigger warnings (for a good reason) from functions called
> out of sock_lock.
> This patch reverts the change introduced by
> 2fa57129d ("RDS: Bypass workqueue when queueing cong updates").
> The patch has been verified for both RDS/TCP as well as RDS/RDMA
> to ensure that there are not regressions for either transport:
> - for verification of RDS/TCP a client-server unit-test was used,
> with the server blocked in gdb and thus unable to drain its rcvbuf,
> eventually triggering a RDS congestion update.
> - for RDS/RDMA, the standard IB regression tests were used
> Signed-off-by: Sowmini Varadhan <>


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