On Wed, Feb 26, 2025 at 04:42:46PM +0100, David Hildenbrand wrote: > On 26.02.25 15:03, Matthew Wilcox wrote: > > On Wed, Feb 26, 2025 at 06:48:15AM -0500, Brian Geffon wrote: > > > When handling faults for anon shmem finish_fault() will attempt to install > > > ptes for the entire folio. Unfortunately if it encounters a single > > > non-pte_none entry in that range it will bail, even if the pte that > > > triggered the fault is still pte_none. When this situation happens the > > > fault will be retried endlessly never making forward progress. > > > > > > This patch fixes this behavior and if it detects that a pte in the range > > > is not pte_none it will fall back to setting just the pte for the > > > address that triggered the fault. > > > > Surely there's a similar problem in do_anonymous_page()? > > I recall we handle it in there correctly the last time I stared at it. > > We check pte_none to decide which folio size we can allocate (including > basing the decision on other factors like VMA etc), and after retaking the > PTL, we recheck vmf_pte_changed / pte_range_none() to make sure there were > no races. Ah, so then we'll retry and allocate a folio of the right size the next time? Rather than the shmem case where the folio is already allocated and we can't change that?
