linux-kernel - Re: [Intel-gfx] [PATCH] Revert "drm/i915/userptr: Acquire the page lock around set_page

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Date:   Thu, 12 Sep 2019 15:39:54 +0100
From:   Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>
To:     Chris Wilson <chris@...is-wilson.co.uk>,
        intel-gfx@...ts.freedesktop.org, torvalds@...ux-foundation.org
Cc:     tiwai@...e.de, linux-kernel@...r.kernel.org, leho@...av.com,
        Jani Nikula <jani.nikula@...el.com>, MKoutny@...e.com,
        stable@...r.kernel.org, Martin.Wilck@...e.com
Subject: Re: [Intel-gfx] [PATCH] Revert "drm/i915/userptr: Acquire the page
 lock around set_page_dirty()"


On 12/09/2019 13:56, Chris Wilson wrote:
> The userptr put_pages can be called from inside try_to_unmap, and so
> enters with the page lock held on one of the object's backing pages. We
> cannot take the page lock ourselves for fear of recursion.
> 
> Reported-by: Lionel Landwerlin <lionel.g.landwerlin@...el.com>
> Reported-by: Martin Wilck <Martin.Wilck@...e.com>
> Reported-by: Leo Kraav <leho@...av.com>
> Fixes: aa56a292ce62 ("drm/i915/userptr: Acquire the page lock around set_page_dirty()")
> References: https://bugzilla.kernel.org/show_bug.cgi?id=203317
> Signed-off-by: Chris Wilson <chris@...is-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@...el.com>
> Cc: Jani Nikula <jani.nikula@...el.com>
> Cc: Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>
> Cc: stable@...r.kernel.org
> ---
>   drivers/gpu/drm/i915/gem/i915_gem_userptr.c | 10 +---------
>   1 file changed, 1 insertion(+), 9 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_userptr.c b/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
> index 74da35611d7c..11b231c187c5 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
> @@ -672,15 +672,7 @@ i915_gem_userptr_put_pages(struct drm_i915_gem_object *obj,
>   
>   	for_each_sgt_page(page, sgt_iter, pages) {
>   		if (obj->mm.dirty)
> -			/*
> -			 * As this may not be anonymous memory (e.g. shmem)
> -			 * but exist on a real mapping, we have to lock
> -			 * the page in order to dirty it -- holding
> -			 * the page reference is not sufficient to
> -			 * prevent the inode from being truncated.
> -			 * Play safe and take the lock.
> -			 */
> -			set_page_dirty_lock(page);
> +			set_page_dirty(page);
>   
>   		mark_page_accessed(page);
>   		put_page(page);
> 

Acked-by: Tvrtko Ursulin <tvrtko.ursulin@...el.com>

Regards,

Tvrtko