On Wed, Nov 22, 2023 at 11:25:28PM -0800, Christoph Hellwig wrote: > On Wed, Nov 15, 2023 at 08:29:01PM -0500, Peter Xu wrote: > > This seems to be a bug not by any report but by code observations. > > > > When GUP sees a devpmd or devpud, it should return whatever value returned > > from follow_devmap_p[mu]d(). If page==NULL returned, it means a fault is > > probably required. Skipping return the NULL should allow the code to fall > > through, which can cause unexpected behavior. > > > > It was there at least before the follow page rework (080dbb618b) in 2017, > > so 6 years. Not yet digging for a Fixes, assuming it can hardly trigger > > even if the logical bug does exist. > > > > Signed-off-by: Peter Xu <peterx@xxxxxxxxxx> > > I'd still add a fixes tag and send if off to Linux for 6.7-rc instead > of letting it linger. Will do. > > Otherwise looks good: > > Reviewed-by: Christoph Hellwig <hch@xxxxxx> When rethinking, "return page" is correct for devmap, but it should be better to always use no_page_table() instead for page==NULL when trying to return NULL for follow_page(), even if no_page_table() should constantly return NULL for devmap, afaict, so it should be the same. So I'll make it slightly different when reposting separately, please feel free to have another look. Thanks, -- Peter Xu
