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From:   Guoqing Jiang <guoqing.jiang@linux.dev>
Subject: Re: [PATCH 2/3] RDMA/rxe: Replace write_lock_bh with
 write_lock_irqsave in __rxe_drop_index
To:     Bob Pearson <rpearsonhpe@gmail.com>,
        Zhu Yanjun <zyjzyj2000@gmail.com>
Cc:     Jason Gunthorpe <jgg@ziepe.ca>,
        RDMA mailing list <linux-rdma@vger.kernel.org>
References: <20220210073655.42281-1-guoqing.jiang@linux.dev>
 <20220210073655.42281-3-guoqing.jiang@linux.dev>
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Message-ID: <b9d5b243-2397-42bd-d833-1a1e5e4ce32c@linux.dev>
Date:   Fri, 11 Feb 2022 18:09:49 +0800
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On 2/10/22 11:49 PM, Bob Pearson wrote:
> On 2/10/22 08:16, Zhu Yanjun wrote:
>> On Thu, Feb 10, 2022 at 3:37 PM Guoqing Jiang<guoqing.jiang@linux.dev>  wrote:
>>> Same as __rxe_add_index, the lock need to be fully IRQ safe, otherwise
>>> below calltrace appears.
>>>
> I had the impression that NAPI ran on a soft IRQ and the rxe tasklets are also on soft IRQs. So at least in theory spin_lock_bh() should be sufficient. Can someone explain where the hard interrupt is coming from that we need to protect.

Since rxe is actually run on top of NIC,  could it comes from NIC if NIC 
driver doesn't switch to NAPI
or from other hardware? But my knowledge about the domain is limited.

>   There are other race conditions in current rxe that may also be the cause of this. I am trying to get a patch series accepted to deal with those.

If possible, could you investigate why rxe after 5.15 kernel doesn't 
work as reported in cover letter? Thank you!

Guoqing