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(No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id E1B7081111; Fri, 7 Jun 2019 19:28:45 +0000 (UTC) Received: from [10.10.120.179] (ovpn-120-179.rdu2.redhat.com [10.10.120.179]) by smtp.corp.redhat.com (Postfix) with ESMTP id E68A410018E0; Fri, 7 Jun 2019 19:28:44 +0000 (UTC) To: Paolo Bonzini , Maxim Levitsky , qemu-block@nongnu.org References: <20190417195355.16123-1-mlevitsk@redhat.com> <20190417195355.16123-2-mlevitsk@redhat.com> <7b9baac9a0b652105cebb681e9759cb4e9d3877b.camel@redhat.com> <601a2a78-0ddb-ccc9-f3c2-46aa16e18629@redhat.com> From: John Snow Openpgp: preference=signencrypt Autocrypt: addr=jsnow@redhat.com; prefer-encrypt=mutual; keydata= mQINBFTKefwBEAChvwqYC6saTzawbih87LqBYq0d5A8jXYXaiFMV/EvMSDqqY4EY6whXliNO IYzhgrPEe7ZmPxbCSe4iMykjhwMh5byIHDoPGDU+FsQty2KXuoxto+ZdrP9gymAgmyqdk3aV vzzmCa3cOppcqKvA0Kqr10UeX/z4OMVV390V+DVWUvzXpda45/Sxup57pk+hyY52wxxjIqef rj8u5BN93s5uCVTus0oiVA6W+iXYzTvVDStMFVqnTxSxlpZoH5RGKvmoWV3uutByQyBPHW2U 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X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Fam Zheng , Kevin Wolf , qemu-devel@nongnu.org, Max Reitz Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 6/7/19 7:08 AM, Paolo Bonzini wrote: > On 06/06/19 23:23, John Snow wrote: >> So: This looks right; does this fix a bug that can be observed? Do we >> have any regression tests for block/NVMe? > > I don't think it fixes a bug; by the time the CQ entry is picked up by > QEMU, the device is not supposed to touch it anymore. > > However, the idea behind the phase bits is that you can decide whether > the driver has placed a completion in the queue. When we get here, we have > > le16_to_cpu(c->status) & 0x1) == !q->cq_phase > > On the next pass through the ring buffer q->cq_phase will be flipped, > and thus when we see this element we'll get > > le16_to_cpu(c->status) & 0x1) == q->cq_phase > > and not process it. Since block/nvme.c flips the bit, this mechanism > does not work and the loop termination relies on the other part of the > condition, "if (!c->cid) break;". > > So the patch is correct, but it would also be nice to also either remove > phase handling altogether, or check that the phase handling works > properly and drop the !c->cid test. > > Paolo > Gotcha, I see, that's why it doesn't cause problems. Thanks :) --js