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Date: Tue, 28 Feb 2017 20:28:08 +0000 From: Lorenzo Stoakes <lstoakes@...il.com> To: Al Viro <viro@...iv.linux.org.uk> Cc: Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, dri-devel@...ts.freedesktop.org, linux-mm <linux-mm@...ck.org> Subject: Re: [PATCH RESEND] drm/via: use get_user_pages_unlocked() On 28 February 2017 at 19:35, Al Viro <viro@...iv.linux.org.uk> wrote: > On Tue, Feb 28, 2017 at 10:01:10AM +0100, Daniel Vetter wrote: > >> > + ret = get_user_pages_unlocked((unsigned long)xfer->mem_addr, >> > + vsg->num_pages, vsg->pages, >> > + (vsg->direction == DMA_FROM_DEVICE) ? FOLL_WRITE : 0); > > Umm... Why not > ret = get_user_pages_fast((unsigned long)xfer->mem_addr, > vsg->num_pages, > vsg->direction == DMA_FROM_DEVICE, > vsg->pages); > > IOW, do you really need a warranty that ->mmap_sem will be grabbed and > released? Daniel will be better placed to answer in this specific case, but more generally is there any reason why we can't just use get_user_pages_fast() in all such cases? These patches were simply a mechanical/cautious replacement for code that is more or less exactly equivalent but if this would make sense perhaps it'd be worth using gup_fast() where possible? -- Lorenzo Stoakes https://ljs.io
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