netdev - Re: [PATCH v2 17/19] powerpc: book3s64: convert to pin_user_pages() and put_user

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Message-ID: <cb3e2acc-0a83-4053-fbcc-6d75dc47f174@nvidia.com>
Date:   Fri, 29 Nov 2019 13:44:53 -0800
From:   John Hubbard <jhubbard@...dia.com>
To:     Jan Kara <jack@...e.cz>
CC:     Andrew Morton <akpm@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Alex Williamson <alex.williamson@...hat.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Björn Töpel <bjorn.topel@...el.com>,
        Christoph Hellwig <hch@...radead.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Dave Chinner <david@...morbit.com>,
        David Airlie <airlied@...ux.ie>,
        "David S . Miller" <davem@...emloft.net>,
        Ira Weiny <ira.weiny@...el.com>,
        Jason Gunthorpe <jgg@...pe.ca>, Jens Axboe <axboe@...nel.dk>,
        Jonathan Corbet <corbet@....net>,
        Jérôme Glisse <jglisse@...hat.com>,
        Magnus Karlsson <magnus.karlsson@...el.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Michal Hocko <mhocko@...e.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Paul Mackerras <paulus@...ba.org>,
        Shuah Khan <shuah@...nel.org>,
        Vlastimil Babka <vbabka@...e.cz>, <bpf@...r.kernel.org>,
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Subject: Re: [PATCH v2 17/19] powerpc: book3s64: convert to pin_user_pages()
 and put_user_page()

On 11/29/19 3:23 AM, Jan Kara wrote:
> On Mon 25-11-19 15:10:33, John Hubbard wrote:
>> 1. Convert from get_user_pages() to pin_user_pages().
>>
>> 2. As required by pin_user_pages(), release these pages via
>> put_user_page(). In this case, do so via put_user_pages_dirty_lock().
>>
>> That has the side effect of calling set_page_dirty_lock(), instead
>> of set_page_dirty(). This is probably more accurate.
> 
> Maybe more accurate but it doesn't work for mm_iommu_unpin(). As I'm
> checking mm_iommu_unpin() gets called from RCU callback which is executed
> interrupt context and you cannot lock pages from such context. So you need
> to queue work from the RCU callback and then do the real work from the
> workqueue...
> 
> 								Honza

ah yes, fixed locally. (In order to avoid  distracting people during the merge
window, I won't post any more versions of the series until the merge window is
over, unless a maintainer tells me that any of these patches are desired for
5.5.)

With that, we are back to a one-line diff for this part:

@@ -215,7 +214,7 @@ static void mm_iommu_unpin(struct mm_iommu_table_group_mem_t *mem)
                 if (mem->hpas[i] & MM_IOMMU_TABLE_GROUP_PAGE_DIRTY)
                         SetPageDirty(page);
  
-               put_page(page);
+               put_user_page(page);
                 mem->hpas[i] = 0;
         }
  }

btw, I'm also working on your feedback for patch 17 (mm/gup: track FOLL_PIN pages [1]),
from a few days earlier, it's not being ignored, I'm just trying to avoid distracting
people during the merge window.

[1] https://lore.kernel.org/r/20191121093941.GA18190@quack2.suse.cz

thanks,
-- 
John Hubbard
NVIDIA