[PATCH 1/2] dax: Pass detailed error code from dax_iomap_fault()

[Jan Kara <jack@suse.cz>]

Ext4 needs to pass through error from its iomap handler to the page
fault handler so that it can properly detect ENOSPC and force
transaction commit and retry the fault (and block allocation). Add
argument to dax_iomap_fault() for passing such error.

Signed-off-by: Jan Kara <jack@suse.cz>
---
 fs/dax.c            | 25 +++++++++++++++----------
 fs/ext2/file.c      |  2 +-
 fs/ext4/file.c      |  2 +-
 fs/xfs/xfs_file.c   |  2 +-
 include/linux/dax.h |  2 +-
 5 files changed, 19 insertions(+), 14 deletions(-)

diff --git a/fs/dax.c b/fs/dax.c
index 78b72c48374e..5bab8210599a 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -872,7 +872,7 @@ static int dax_iomap_pfn(struct iomap *iomap, loff_t pos, size_t size,
  * point to real DAX storage instead.
  */
 static int dax_load_hole(struct address_space *mapping, void *entry,
-			 struct vm_fault *vmf)
+			 struct vm_fault *vmf, int *errp)
 {
 	struct inode *inode = mapping->host;
 	unsigned long vaddr = vmf->address;
@@ -890,6 +890,8 @@ static int dax_load_hole(struct address_space *mapping, void *entry,
 			RADIX_DAX_ZERO_PAGE, false);
 	if (IS_ERR(entry2)) {
 		ret = VM_FAULT_SIGBUS;
+		if (errp)
+			*errp = PTR_ERR(entry2);
 		goto out;
 	}
 
@@ -1076,10 +1078,12 @@ dax_iomap_rw(struct kiocb *iocb, struct iov_iter *iter,
 }
 EXPORT_SYMBOL_GPL(dax_iomap_rw);
 
-static int dax_fault_return(int error)
+static int dax_fault_return(int error, int *errp)
 {
 	if (error == 0)
 		return VM_FAULT_NOPAGE;
+	if (errp)
+		*errp = error;
 	if (error == -ENOMEM)
 		return VM_FAULT_OOM;
 	return VM_FAULT_SIGBUS;
@@ -1096,7 +1100,7 @@ static bool dax_fault_is_synchronous(unsigned long flags,
 		&& (iomap->flags & IOMAP_F_DIRTY);
 }
 
-static int dax_iomap_pte_fault(struct vm_fault *vmf, pfn_t *pfnp,
+static int dax_iomap_pte_fault(struct vm_fault *vmf, pfn_t *pfnp, int *errp,
 			       const struct iomap_ops *ops)
 {
 	struct vm_area_struct *vma = vmf->vma;
@@ -1129,7 +1133,7 @@ static int dax_iomap_pte_fault(struct vm_fault *vmf, pfn_t *pfnp,
 
 	entry = grab_mapping_entry(mapping, vmf->pgoff, 0);
 	if (IS_ERR(entry)) {
-		vmf_ret = dax_fault_return(PTR_ERR(entry));
+		vmf_ret = dax_fault_return(PTR_ERR(entry), errp);
 		goto out;
 	}
 
@@ -1151,7 +1155,7 @@ static int dax_iomap_pte_fault(struct vm_fault *vmf, pfn_t *pfnp,
 	 */
 	error = ops->iomap_begin(inode, pos, PAGE_SIZE, flags, &iomap);
 	if (error) {
-		vmf_ret = dax_fault_return(error);
+		vmf_ret = dax_fault_return(error, errp);
 		goto unlock_entry;
 	}
 	if (WARN_ON_ONCE(iomap.offset + iomap.length < pos + PAGE_SIZE)) {
@@ -1236,7 +1240,7 @@ static int dax_iomap_pte_fault(struct vm_fault *vmf, pfn_t *pfnp,
 	case IOMAP_UNWRITTEN:
 	case IOMAP_HOLE:
 		if (!write) {
-			vmf_ret = dax_load_hole(mapping, entry, vmf);
+			vmf_ret = dax_load_hole(mapping, entry, vmf, errp);
 			goto finish_iomap;
 		}
 		/*FALLTHRU*/
@@ -1247,7 +1251,7 @@ static int dax_iomap_pte_fault(struct vm_fault *vmf, pfn_t *pfnp,
 	}
 
  error_finish_iomap:
-	vmf_ret = dax_fault_return(error) | major;
+	vmf_ret = dax_fault_return(error, errp) | major;
  finish_iomap:
 	if (ops->iomap_end) {
 		int copied = PAGE_SIZE;
@@ -1489,6 +1493,7 @@ static int dax_iomap_pmd_fault(struct vm_fault *vmf, pfn_t *pfnp,
  * @vmf: The description of the fault
  * @pe_size: Size of the page to fault in
  * @pfnp: PFN to insert for synchronous faults if fsync is required
+ * @errp: Storage for detailed error code in case of error
  * @ops: Iomap ops passed from the file system
  *
  * When a page fault occurs, filesystems may call this helper in
@@ -1497,11 +1502,11 @@ static int dax_iomap_pmd_fault(struct vm_fault *vmf, pfn_t *pfnp,
  * successfully.
  */
 int dax_iomap_fault(struct vm_fault *vmf, enum page_entry_size pe_size,
-		    pfn_t *pfnp, const struct iomap_ops *ops)
+		    pfn_t *pfnp, int *errp, const struct iomap_ops *ops)
 {
 	switch (pe_size) {
 	case PE_SIZE_PTE:
-		return dax_iomap_pte_fault(vmf, pfnp, ops);
+		return dax_iomap_pte_fault(vmf, pfnp, errp, ops);
 	case PE_SIZE_PMD:
 		return dax_iomap_pmd_fault(vmf, pfnp, ops);
 	default:
@@ -1547,7 +1552,7 @@ static int dax_insert_pfn_mkwrite(struct vm_fault *vmf,
 	switch (pe_size) {
 	case PE_SIZE_PTE:
 		error = vm_insert_mixed_mkwrite(vmf->vma, vmf->address, pfn);
-		vmf_ret = dax_fault_return(error);
+		vmf_ret = dax_fault_return(error, NULL);
 		break;
 #ifdef CONFIG_FS_DAX_PMD
 	case PE_SIZE_PMD:
diff --git a/fs/ext2/file.c b/fs/ext2/file.c
index 2da67699dc33..09640220fda8 100644
--- a/fs/ext2/file.c
+++ b/fs/ext2/file.c
@@ -100,7 +100,7 @@ static int ext2_dax_fault(struct vm_fault *vmf)
 	}
 	down_read(&ei->dax_sem);
 
-	ret = dax_iomap_fault(vmf, PE_SIZE_PTE, NULL, &ext2_iomap_ops);
+	ret = dax_iomap_fault(vmf, PE_SIZE_PTE, NULL, NULL, &ext2_iomap_ops);
 
 	up_read(&ei->dax_sem);
 	if (vmf->flags & FAULT_FLAG_WRITE)
diff --git a/fs/ext4/file.c b/fs/ext4/file.c
index a0ae27b1bc66..1c7cd882d998 100644
--- a/fs/ext4/file.c
+++ b/fs/ext4/file.c
@@ -314,7 +314,7 @@ static int ext4_dax_huge_fault(struct vm_fault *vmf,
 	} else {
 		down_read(&EXT4_I(inode)->i_mmap_sem);
 	}
-	result = dax_iomap_fault(vmf, pe_size, &pfn, &ext4_iomap_ops);
+	result = dax_iomap_fault(vmf, pe_size, &pfn, NULL, &ext4_iomap_ops);
 	if (write) {
 		ext4_journal_stop(handle);
 		/* Handling synchronous page fault? */
diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index 8601275cc5e6..9ea08326f876 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -1048,7 +1048,7 @@ __xfs_filemap_fault(
 	if (IS_DAX(inode)) {
 		pfn_t pfn;
 
-		ret = dax_iomap_fault(vmf, pe_size, &pfn, &xfs_iomap_ops);
+		ret = dax_iomap_fault(vmf, pe_size, &pfn, NULL, &xfs_iomap_ops);
 		if (ret & VM_FAULT_NEEDDSYNC)
 			ret = dax_finish_sync_fault(vmf, pe_size, pfn);
 	} else {
diff --git a/include/linux/dax.h b/include/linux/dax.h
index 5258346c558c..0185ecdae135 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -96,7 +96,7 @@ bool dax_write_cache_enabled(struct dax_device *dax_dev);
 ssize_t dax_iomap_rw(struct kiocb *iocb, struct iov_iter *iter,
 		const struct iomap_ops *ops);
 int dax_iomap_fault(struct vm_fault *vmf, enum page_entry_size pe_size,
-		    pfn_t *pfnp, const struct iomap_ops *ops);
+		    pfn_t *pfnp, int *errp, const struct iomap_ops *ops);
 int dax_finish_sync_fault(struct vm_fault *vmf, enum page_entry_size pe_size,
 			  pfn_t pfn);
 int dax_delete_mapping_entry(struct address_space *mapping, pgoff_t index);
-- 
2.12.3

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