linux-kernel - Re: [RFC PATCH] usb: host: xhci: allow __GFP

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Message-ID: <1558614729.3994.5.camel@suse.com>
Date:   Thu, 23 May 2019 14:32:09 +0200
From:   Oliver Neukum <oneukum@...e.com>
To:     Christoph Hellwig <hch@...radead.org>,
        Jaewon Kim <jaewon31.kim@...il.com>
Cc:     linux-mm@...ck.org, gregkh@...uxfoundation.org,
        Jaewon Kim <jaewon31.kim@...sung.com>,
        m.szyprowski@...sung.com, ytk.lee@...sung.com,
        linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org
Subject: Re: [RFC PATCH] usb: host: xhci: allow __GFP_FS in dma allocation

On So, 2019-05-19 at 22:56 -0700, Christoph Hellwig wrote:
> Folks, you can't just pass arbitary GFP_ flags to dma allocation
> routines, beause very often they are not just wrappers around
> the page allocator.
> 
> So no, you can't just fine grained control the flags, but the
> existing code is just as buggy.
> 
> Please switch to use memalloc_noio_save() instead.

Thinking about this again, we have a problem. We introduced
memalloc_noio_save() in 3.10 . Hence the code should have been
correct in v4.14. Which means that either
6518202970c1 "(mm/cma: remove unsupported gfp_mask
parameter from cma_alloc()"
is buggy, or the original issue with a delay of 2 seconds
still exist.

Do we need to do something?

	Regards
		Oliver