Re: [PATCH AUTOSEL 5.2 13/23] drm/i915/userptr: Acquire the page lock around set_page_dirty()

[Sasha Levin]

On Thu, Sep 12, 2019 at 11:51:33PM +0300, Thomas Backlund wrote:
> Den 03-09-2019 kl. 19:24, skrev Sasha Levin:
> > From: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> >
> > [ Upstream commit aa56a292ce623734ddd30f52d73f527d1f3529b5 ]
> >
> > set_page_dirty says:
> >
> > 	For pages with a mapping this should be done under the page lock
> > 	for the benefit of asynchronous memory errors who prefer a
> > 	consistent dirty state. This rule can be broken in some special
> > 	cases, but should be better not to.
> >
> > Under those rules, it is only safe for us to use the plain set_page_dirty
> > calls for shmemfs/anonymous memory. Userptr may be used with real
> > mappings and so needs to use the locked version (set_page_dirty_lock).
> >
> > Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=203317
> > Fixes: 5cc9ed4b9a7a ("drm/i915: Introduce mapping of user pages into video memory (userptr) ioctl")
> > References: 6dcc693bc57f ("ext4: warn when page is dirtied without buffers")
> > Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> > Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
> > Cc: stable@xxxxxxxxxxxxxxx
> > Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
> > Link: https://patchwork.freedesktop.org/patch/msgid/20190708140327.26825-1-chris@xxxxxxxxxxxxxxxxxx
> > (cherry picked from commit cb6d7c7dc7ff8cace666ddec66334117a6068ce2)
> > Signed-off-by: Jani Nikula <jani.nikula@xxxxxxxxx>
> > Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
> > ---
> >  drivers/gpu/drm/i915/i915_gem_userptr.c | 10 +++++++++-
> >  1 file changed, 9 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/i915/i915_gem_userptr.c b/drivers/gpu/drm/i915/i915_gem_userptr.c
> > index 8079ea3af1039..b1fc15c7f5997 100644
> > --- a/drivers/gpu/drm/i915/i915_gem_userptr.c
> > +++ b/drivers/gpu/drm/i915/i915_gem_userptr.c
> > @@ -678,7 +678,15 @@ 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);
> > +			/*
> > +			 * 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);
> >  		mark_page_accessed(page);
> >  		put_page(page);
>
>
> Please drop this one from all 5.2 and 4.19 stable queues
>
> It has now been reverted in Linus tree:
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=505a8ec7e11ae5236c4a154a1e24ef49a8349600

Now dropped, thank you.

--
Thanks,
Sasha