linux-kernel - Re: [PATCH 06/34] drm/i915: convert put_page() to put_user

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Message-ID: <7d9a9c57-4322-270b-b636-7214019f87e9@nvidia.com>
Date:   Fri, 2 Aug 2019 11:48:08 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        <john.hubbard@...il.com>
CC:     Christoph Hellwig <hch@...radead.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Chinner <david@...morbit.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Ira Weiny <ira.weiny@...el.com>, Jan Kara <jack@...e.cz>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Jérôme Glisse <jglisse@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        <amd-gfx@...ts.freedesktop.org>, <ceph-devel@...r.kernel.org>,
        <devel@...verdev.osuosl.org>, <devel@...ts.orangefs.org>,
        <dri-devel@...ts.freedesktop.org>,
        <intel-gfx@...ts.freedesktop.org>, <kvm@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-block@...r.kernel.org>, <linux-crypto@...r.kernel.org>,
        <linux-fbdev@...r.kernel.org>, <linux-fsdevel@...r.kernel.org>,
        <linux-media@...r.kernel.org>, <linux-mm@...ck.org>,
        <linux-nfs@...r.kernel.org>, <linux-rdma@...r.kernel.org>,
        <linux-rpi-kernel@...ts.infradead.org>,
        <linux-xfs@...r.kernel.org>, <netdev@...r.kernel.org>,
        <rds-devel@....oracle.com>, <sparclinux@...r.kernel.org>,
        <x86@...nel.org>, <xen-devel@...ts.xenproject.org>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        David Airlie <airlied@...ux.ie>
Subject: Re: [PATCH 06/34] drm/i915: convert put_page() to put_user_page*()

On 8/2/19 2:19 AM, Joonas Lahtinen wrote:
> Quoting john.hubbard@...il.com (2019-08-02 05:19:37)
>> From: John Hubbard <jhubbard@...dia.com>
>>
>> For pages that were retained via get_user_pages*(), release those pages
>> via the new put_user_page*() routines, instead of via put_page() or
>> release_pages().
>>
>> This is part a tree-wide conversion, as described in commit fc1d8e7cca2d
>> ("mm: introduce put_user_page*(), placeholder versions").
>>
>> Note that this effectively changes the code's behavior in
>> i915_gem_userptr_put_pages(): it now calls set_page_dirty_lock(),
>> instead of set_page_dirty(). This is probably more accurate.
> 
> We've already fixed this in drm-tip where the current code uses
> set_page_dirty_lock().
> 
> This would conflict with our tree. Rodrigo is handling
> drm-intel-next for 5.4, so you guys want to coordinate how
> to merge.
> 

Hi Joonas, Rodrigo,

First of all, I apologize for the API breakage: put_user_pages_dirty_lock()
has an additional "dirty" parameter.

In order to deal with the merge problem, I'll drop this patch from my series,
and I'd recommend that the drm-intel-next take the following approach:

1) For now, s/put_page/put_user_page/ in i915_gem_userptr_put_pages(),
and fix up the set_page_dirty() --> set_page_dirty_lock() issue, like this
(based against linux.git):

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_userptr.c 
b/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
index 528b61678334..94721cc0093b 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
@@ -664,10 +664,10 @@ i915_gem_userptr_put_pages(struct drm_i915_gem_object *obj,

         for_each_sgt_page(page, sgt_iter, pages) {
                 if (obj->mm.dirty)
-                       set_page_dirty(page);
+                       set_page_dirty_lock(page);

                 mark_page_accessed(page);
-               put_page(page);
+               put_user_page(page);
         }
         obj->mm.dirty = false;


That will leave you with your original set_page_dirty_lock() calls
and everything works properly.

2) Next cycle, move to the new put_user_pages_dirty_lock().

thanks,
-- 
John Hubbard
NVIDIA


> Regards, Joonas
>