search for: folio_try_get

...se we don't hold + * the PTL so a racing thread can remove the device-exclusive + * entry and unmap it. If the folio is free the entry must + * have been removed already. If it happens to have already + * been re-allocated after being freed all we do is lock and + * unlock it. + */ + if (!folio_try_get(folio)) + return 0; + + if (!folio_lock_or_retry(folio, vma->vm_mm, vmf->flags)) { + folio_put(folio); return VM_FAULT_RETRY; + } mmu_notifier_range_init_owner(&range, MMU_NOTIFY_EXCLUSIVE, 0, vma->vm_mm, vmf->address & PAGE_MASK, (vmf->address & PAGE_MAS...

...t have been removed already. > + */ > + if (!get_page_unless_zero(vmf->page)) > + return 0; >From a folio point of view: what the hell are you doing here? Tail pages don't have individual refcounts; all the refcounts are actually taken on the folio. So this should be: if (!folio_try_get(folio)) return 0; (you can fix up the comment yourself) > + if (!folio_lock_or_retry(folio, vma->vm_mm, vmf->flags)) { > + put_page(vmf->page); folio_put(folio); > return VM_FAULT_RETRY; > + } > mmu_notifier_range_init_owner(&range, MMU_NOTIFY_EXCLUSIVE, 0, v...

Device exclusive page table entries are used to prevent CPU access to a page whilst it is being accessed from a device. Typically this is used to implement atomic operations when the underlying bus does not support atomic access. When a CPU thread encounters a device exclusive entry it locks the page and restores the original entry after calling mmu notifiers to signal drivers that exclusive