[PATCH v3 4/8] mm: replace folio_lock_or_retry with folio_lock_fault

[Suren Baghdasaryan <surenb@xxxxxxxxxx>]

Change folio_lock_or_retry to accept vm_fault struct and return the
vm_fault_t directly. This will be used later to return additional
information about the state of the mmap_lock upon return from this
function.

Suggested-by: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
---
 include/linux/pagemap.h | 13 ++++++-------
 mm/filemap.c            | 29 +++++++++++++++--------------
 mm/memory.c             | 14 ++++++--------
 3 files changed, 27 insertions(+), 29 deletions(-)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index a56308a9d1a4..0bc206c6f62c 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -896,8 +896,7 @@ static inline bool wake_page_match(struct wait_page_queue *wait_page,
 
 void __folio_lock(struct folio *folio);
 int __folio_lock_killable(struct folio *folio);
-bool __folio_lock_or_retry(struct folio *folio, struct mm_struct *mm,
-				unsigned int flags);
+vm_fault_t __folio_lock_fault(struct folio *folio, struct vm_fault *vmf);
 void unlock_page(struct page *page);
 void folio_unlock(struct folio *folio);
 
@@ -995,17 +994,17 @@ static inline int folio_lock_killable(struct folio *folio)
 }
 
 /*
- * folio_lock_or_retry - Lock the folio, unless this would block and the
+ * folio_lock_fault - Lock the folio, unless this would block and the
  * caller indicated that it can handle a retry.
  *
  * Return value and mmap_lock implications depend on flags; see
- * __folio_lock_or_retry().
+ * __folio_lock_fault().
  */
-static inline bool folio_lock_or_retry(struct folio *folio,
-		struct mm_struct *mm, unsigned int flags)
+static inline vm_fault_t folio_lock_fault(struct folio *folio,
+					  struct vm_fault *vmf)
 {
 	might_sleep();
-	return folio_trylock(folio) || __folio_lock_or_retry(folio, mm, flags);
+	return folio_trylock(folio) ? 0 : __folio_lock_fault(folio, vmf);
 }
 
 /*
diff --git a/mm/filemap.c b/mm/filemap.c
index 00f01d8ead47..87b335a93530 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1701,46 +1701,47 @@ static int __folio_lock_async(struct folio *folio, struct wait_page_queue *wait)
 
 /*
  * Return values:
- * true - folio is locked; mmap_lock is still held.
- * false - folio is not locked.
+ * 0 - folio is locked.
+ * VM_FAULT_RETRY - folio is not locked.
  *     mmap_lock has been released (mmap_read_unlock(), unless flags had both
  *     FAULT_FLAG_ALLOW_RETRY and FAULT_FLAG_RETRY_NOWAIT set, in
  *     which case mmap_lock is still held.
  *
- * If neither ALLOW_RETRY nor KILLABLE are set, will always return true
+ * If neither ALLOW_RETRY nor KILLABLE are set, will always return 0
  * with the folio locked and the mmap_lock unperturbed.
  */
-bool __folio_lock_or_retry(struct folio *folio, struct mm_struct *mm,
-			 unsigned int flags)
+vm_fault_t __folio_lock_fault(struct folio *folio, struct vm_fault *vmf)
 {
-	if (fault_flag_allow_retry_first(flags)) {
+	struct mm_struct *mm = vmf->vma->vm_mm;
+
+	if (fault_flag_allow_retry_first(vmf->flags)) {
 		/*
 		 * CAUTION! In this case, mmap_lock is not released
-		 * even though return 0.
+		 * even though return VM_FAULT_RETRY.
 		 */
-		if (flags & FAULT_FLAG_RETRY_NOWAIT)
-			return false;
+		if (vmf->flags & FAULT_FLAG_RETRY_NOWAIT)
+			return VM_FAULT_RETRY;
 
 		mmap_read_unlock(mm);
-		if (flags & FAULT_FLAG_KILLABLE)
+		if (vmf->flags & FAULT_FLAG_KILLABLE)
 			folio_wait_locked_killable(folio);
 		else
 			folio_wait_locked(folio);
-		return false;
+		return VM_FAULT_RETRY;
 	}
-	if (flags & FAULT_FLAG_KILLABLE) {
+	if (vmf->flags & FAULT_FLAG_KILLABLE) {
 		bool ret;
 
 		ret = __folio_lock_killable(folio);
 		if (ret) {
 			mmap_read_unlock(mm);
-			return false;
+			return VM_FAULT_RETRY;
 		}
 	} else {
 		__folio_lock(folio);
 	}
 
-	return true;
+	return 0;
 }
 
 /**
diff --git a/mm/memory.c b/mm/memory.c
index 9011ad63c41b..3c2acafcd7b6 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3568,6 +3568,7 @@ static vm_fault_t remove_device_exclusive_entry(struct vm_fault *vmf)
 	struct folio *folio = page_folio(vmf->page);
 	struct vm_area_struct *vma = vmf->vma;
 	struct mmu_notifier_range range;
+	vm_fault_t ret;
 
 	/*
 	 * We need a reference to lock the folio because we don't hold
@@ -3580,9 +3581,10 @@ static vm_fault_t remove_device_exclusive_entry(struct vm_fault *vmf)
 	if (!folio_try_get(folio))
 		return 0;
 
-	if (!folio_lock_or_retry(folio, vma->vm_mm, vmf->flags)) {
+	ret = folio_lock_fault(folio, vmf);
+	if (ret) {
 		folio_put(folio);
-		return VM_FAULT_RETRY;
+		return ret;
 	}
 	mmu_notifier_range_init_owner(&range, MMU_NOTIFY_EXCLUSIVE, 0,
 				vma->vm_mm, vmf->address & PAGE_MASK,
@@ -3704,7 +3706,6 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
 	bool exclusive = false;
 	swp_entry_t entry;
 	pte_t pte;
-	int locked;
 	vm_fault_t ret = 0;
 	void *shadow = NULL;
 
@@ -3825,12 +3826,9 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
 		goto out_release;
 	}
 
-	locked = folio_lock_or_retry(folio, vma->vm_mm, vmf->flags);
-
-	if (!locked) {
-		ret |= VM_FAULT_RETRY;
+	ret |= folio_lock_fault(folio, vmf);
+	if (ret & VM_FAULT_RETRY)
 		goto out_release;
-	}
 
 	if (swapcache) {
 		/*
-- 
2.41.0.178.g377b9f9a00-goog