linux-kernel - Re: [PATCH V2 3/3] Adding device_dma_parameters->offset_preserve

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Date:   Mon, 1 Feb 2021 23:59:52 +0000
From:   Chaitanya Kulkarni <Chaitanya.Kulkarni@....com>
To:     Jianxiong Gao <jxgao@...gle.com>, Keith Busch <kbusch@...nel.org>
CC:     "heikki.krogerus@...ux.intel.com" <heikki.krogerus@...ux.intel.com>,
        "sagi@...mberg.me" <sagi@...mberg.me>,
        Saravana Kannan <saravanak@...gle.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Marc Orr <marcorr@...gle.com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "rafael.j.wysocki@...el.com" <rafael.j.wysocki@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-nvme@...ts.infradead.org" <linux-nvme@...ts.infradead.org>,
        "axboe@...com" <axboe@...com>,
        "bgolaszewski@...libre.com" <bgolaszewski@...libre.com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "jroedel@...e.de" <jroedel@...e.de>,
        Erdem Aktas <erdemaktas@...gle.com>,
        "dan.j.williams@...el.com" <dan.j.williams@...el.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Robin Murphy <robin.murphy@....com>,
        Christoph Hellwig <hch@....de>,
        "m.szyprowski@...sung.com" <m.szyprowski@...sung.com>
Subject: Re: [PATCH V2 3/3] Adding device_dma_parameters->offset_preserve_mask
 to NVMe driver.

On 2/1/21 13:27, Jianxiong Gao wrote:
>> Why is this setting being done and undone on each IO? Wouldn't it be
>> more efficient to set it once during device initialization?
>>
>> And more importantly, this isn't thread safe: one CPU may be setting the
>> device's dma alignment mask to 0 while another CPU is expecting it to be
>> NVME_CTRL_PAGE_SIZE - 1.
>  I was having trouble getting the OS booted when setting it once during
>  initialization. However when I rebased to the latest rc6 this morning it
>  seems to be working with setting the mask on probe. I am still testing out
>  and will appreciate any idea what may cause the nvme driver to fail
>  with a single mask.
Based on the Keith's comment it needs to be completely avoided in hot path.

Did you get a chance to bisect the problem in the rc6 ? We need to know the
root cause otherwise it might happen again after we add this patch.