On Fri, Nov 23, 2018 at 01:47:32PM +0300, Kirill A. Shutemov wrote: > On Thu, Nov 22, 2018 at 01:32:23PM -0800, Matthew Wilcox wrote: > > After we establish a reference on the page, we check the pointer continues > > to be in the correct position in i_pages. There's no need to check the > > page->mapping or page->index afterwards; if those can change after we've > > got the reference, they can change after we return the page to the caller. > > Hm. IIRC, page->mapping can be set to NULL due truncation, but what about > index? When it can be changed? Truncation doesn't touch it. I think index can only be changed after the refcount has hit zero and the page is safely out of the pagecache. I agree that page->mapping can be set to NULL after the call to xas_reload() ... but then it can also happen after the check, so the check isn't really buying us anything that the xas_reload() call doesn't already check.
