On 12/05/2016 06:43 AM, Max Gurtovoy wrote:
hi guys,
I've noticed that we use ib_drain_rq in teardown flow in ib_srp driver.
Trying to figure out why is this better than ib_drain_qp ?
BTW, the recv_cq != send_cq in srp so it's even better to use
ib_drain_qp, isn't it ?
I haven't encountered a bug in this area yet, but just trying to
understand if it's there.
Hello Max,
The description of a patch that was accepted upstream about two years
ago explains the purpose of the ib_drain_rq() call:
commit 7dad6b2e440d810273946b0e7092a8fe043c3b8a
Author: Bart Van Assche <bvanassche@xxxxxxx>
Date: Tue Oct 21 18:00:35 2014 +0200
IB/srp: Fix a race condition triggered by destroying a queue pair
At least LID reassignment can trigger a race condition in the SRP
initiator driver, namely the receive completion handler trying to
post a request on a QP during or after QP destruction and before
the CQ's have been destroyed. Avoid this race by modifying a QP
into the error state and by waiting until all receive completions
have been processed before destroying a QP.
Reported-by: Max Gurtuvoy <maxg@xxxxxxxxxxxx>
Signed-off-by: Bart Van Assche <bvanassche@xxxxxxx>
Reviewed-by: Sagi Grimberg <sagig@xxxxxxxxxxxx>
Signed-off-by: Christoph Hellwig <hch@xxxxxx>
There is no risk that any send work will be posted while the ib_srp
driver destroys a QP.
Bart.
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