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?