Hi, On Mon 09-07-18 01:05:52, john.hubbard@xxxxxxxxx wrote: > From: John Hubbard <jhubbard@xxxxxxxxxx> > > With respect to tracking get_user_pages*() pages with page->dma_pinned* > fields [1], I spent a few days retrofitting most of the get_user_pages*() > call sites, by adding calls to a new put_user_page() function, in place > of put_page(), where appropriate. This will work, but it's a large effort. > > Design note: I didn't see anything that hinted at a way to fix this > problem, without actually changing all of the get_user_pages*() call sites, > so I think it's reasonable to start with that. Agreed. > Anyway, it's still incomplete, but because this is a large, tree-wide > change (that will take some time and testing), I'd like to propose a plan, > before spamming zillions of people with put_user_page() conversion patches. > So I picked out the first two patches to show where this is going. > > Proposed steps: > > Step 1: > > Start with the patches here, then continue with...dozens more. > This will eventually convert all of the call sites to use put_user_page(). > This is easy in some places, but complex in others, such as: > > -- drivers/gpu/drm/amd > -- bio > -- fuse > -- cifs > -- anything from: > git grep iov_iter_get_pages | cut -f1 -d ':' | sort | uniq > > The easy ones can be grouped into a single patchset, perhaps, and the > complex ones probably each need a patchset, in order to get the in-depth > review they'll need. Agreed. > Furthermore, some of these areas I hope to attract some help on, once > this starts going. > > Step 2: > > In parallel, tidy up the core patchset that was discussed in [1], (version > 2 has already been reviewed, so I know what to do), and get it perfected > and reviewed. Don't apply it until step 1 is all done, though. > > Step 3: > > Activate refcounting of dma-pinned pages (essentially, patch #5, which is > [1]), but don't use it yet. Place a few WARN_ON_ONCE calls to start > mopping up any missed call sites. > > Step 4: > > After some soak time, actually connect it up (patch #6 of [1]) and start > taking action based on the new page->dma_pinned* fields. > > [1] https://www.spinics.net/lists/linux-mm/msg156409.html > > or, the same thread on LKML if it's working for you: > > https://lkml.org/lkml/2018/7/4/368 Yeah, but as Nick pointed out we have some more work to do in step 4 to avoid deadlocks. Still there's a lot of work to do on which the direction to progress is clear :). Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
