linux-kernel - Re: Why CMA allocater fails if there is a signal pending?

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Message-ID: <20190325102633.v6hkvda6q7462wza@shell.armlinux.org.uk>
Date:   Mon, 25 Mar 2019 10:26:33 +0000
From:   Russell King - ARM Linux admin <linux@...linux.org.uk>
To:     Peter Chen <hzpeterchen@...il.com>
Cc:     Michal Nazarewicz <mina86@...a86.com>, peter.chen@....com,
        fugang.duan@....com, linux-usb@...r.kernel.org,
        lkml <linux-kernel@...r.kernel.org>, linux-mm@...ck.org,
        linux-arm-kernel@...ts.infradead.org,
        Marek Szyprowski <m.szyprowski@...sung.com>
Subject: Re: Why CMA allocater fails if there is a signal pending?

On Mon, Mar 25, 2019 at 04:37:09PM +0800, Peter Chen wrote:
> Hi Michal & Marek,
> 
> I meet an issue that the DMA (CMA used) allocation failed if there is a user
> signal, Eg Ctrl+C, it causes the USB xHCI stack fails to resume due to
> dma_alloc_coherent
> failed. It can be easy to reproduce if the user press Ctrl+C at
> suspend/resume test.

It has been possible in the past for cma_alloc() to take seconds or
longer to allocate, depending on the size of the CMA area and the
number of pinned GFP_MOVABLE pages within the CMA area.  Whether that
is true of today's CMA or not, I don't know.

It's probably there to allow such a situation to be recoverable, but
is not a good idea if we're expecting dma_alloc_*() not to fail in
those scenarios.

-- 
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