[PATCH 1/4] mm: gup: add FOLL_TRIED

[Andrea Arcangeli <aarcange@redhat.com>]

From: Andres Lagar-Cavilla <andreslc@google.com>

Reviewed-by: Radim KrA?mA!A? <rkrcmar@redhat.com>
Signed-off-by: Andres Lagar-Cavilla <andreslc@google.com>
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
---
 include/linux/mm.h | 1 +
 mm/gup.c           | 4 ++++
 2 files changed, 5 insertions(+)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 8981cc8..0f4196a 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1985,6 +1985,7 @@ static inline struct page *follow_page(struct vm_area_struct *vma,
 #define FOLL_HWPOISON	0x100	/* check page is hwpoisoned */
 #define FOLL_NUMA	0x200	/* force NUMA hinting page fault */
 #define FOLL_MIGRATION	0x400	/* wait for page to replace migration entry */
+#define FOLL_TRIED	0x800	/* a retry, previous pass started an IO */
 
 typedef int (*pte_fn_t)(pte_t *pte, pgtable_t token, unsigned long addr,
 			void *data);
diff --git a/mm/gup.c b/mm/gup.c
index 91d044b..af7ea3e 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -281,6 +281,10 @@ static int faultin_page(struct task_struct *tsk, struct vm_area_struct *vma,
 		fault_flags |= FAULT_FLAG_ALLOW_RETRY;
 	if (*flags & FOLL_NOWAIT)
 		fault_flags |= FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_RETRY_NOWAIT;
+	if (*flags & FOLL_TRIED) {
+		VM_WARN_ON_ONCE(fault_flags & FAULT_FLAG_ALLOW_RETRY);
+		fault_flags |= FAULT_FLAG_TRIED;
+	}
 
 	ret = handle_mm_fault(mm, vma, address, fault_flags);
 	if (ret & VM_FAULT_ERROR) {

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