ext4 crypto: don't let data integrity writebacks fail with ENOMEM

We don't want the writeback triggered from the journal commit (in
data=writeback mode) to cause the journal to abort due to
generic_writepages() returning an ENOMEM error.  In addition, if
fsync() fails with ENOMEM, most applications will probably not do the
right thing.

So if we are doing a data integrity sync, and ext4_encrypt() returns
ENOMEM, we will submit any queued I/O to date, and then retry the
allocation using GFP_NOFAIL.

Google-Bug-Id: 27641567
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/crypto.c

@@ -91,7 +91,8 @@ void ext4_release_crypto_ctx(struct ext4_crypto_ctx *ctx)
  * Return: An allocated and initialized encryption context on success; error
  * value or NULL otherwise.
  */
-struct ext4_crypto_ctx *ext4_get_crypto_ctx(struct inode *inode)
+struct ext4_crypto_ctx *ext4_get_crypto_ctx(struct inode *inode,
+					    gfp_t gfp_flags)
 {
 	struct ext4_crypto_ctx *ctx = NULL;
 	int res = 0;
@@ -118,7 +119,7 @@ struct ext4_crypto_ctx *ext4_get_crypto_ctx(struct inode *inode)
 		list_del(&ctx->free_list);
 	spin_unlock_irqrestore(&ext4_crypto_ctx_lock, flags);
 	if (!ctx) {
-		ctx = kmem_cache_zalloc(ext4_crypto_ctx_cachep, GFP_NOFS);
+		ctx = kmem_cache_zalloc(ext4_crypto_ctx_cachep, gfp_flags);
 		if (!ctx) {
 			res = -ENOMEM;
 			goto out;
@@ -255,7 +256,8 @@ static int ext4_page_crypto(struct inode *inode,
 			    ext4_direction_t rw,
 			    pgoff_t index,
 			    struct page *src_page,
-			    struct page *dest_page)
+			    struct page *dest_page,
+			    gfp_t gfp_flags)
 
 {
 	u8 xts_tweak[EXT4_XTS_TWEAK_SIZE];
@@ -266,7 +268,7 @@ static int ext4_page_crypto(struct inode *inode,
 	struct crypto_skcipher *tfm = ci->ci_ctfm;
 	int res = 0;
 
-	req = skcipher_request_alloc(tfm, GFP_NOFS);
+	req = skcipher_request_alloc(tfm, gfp_flags);
 	if (!req) {
 		printk_ratelimited(KERN_ERR
 				   "%s: crypto_request_alloc() failed\n",
@@ -307,9 +309,10 @@ static int ext4_page_crypto(struct inode *inode,
 	return 0;
 }
 
-static struct page *alloc_bounce_page(struct ext4_crypto_ctx *ctx)
+static struct page *alloc_bounce_page(struct ext4_crypto_ctx *ctx,
+				      gfp_t gfp_flags)
 {
-	ctx->w.bounce_page = mempool_alloc(ext4_bounce_page_pool, GFP_NOWAIT);
+	ctx->w.bounce_page = mempool_alloc(ext4_bounce_page_pool, gfp_flags);
 	if (ctx->w.bounce_page == NULL)
 		return ERR_PTR(-ENOMEM);
 	ctx->flags |= EXT4_WRITE_PATH_FL;
@@ -332,7 +335,8 @@ static struct page *alloc_bounce_page(struct ext4_crypto_ctx *ctx)
  * error value or NULL.
  */
 struct page *ext4_encrypt(struct inode *inode,
-			  struct page *plaintext_page)
+			  struct page *plaintext_page,
+			  gfp_t gfp_flags)
 {
 	struct ext4_crypto_ctx *ctx;
 	struct page *ciphertext_page = NULL;
@@ -340,17 +344,17 @@ struct page *ext4_encrypt(struct inode *inode,
 
 	BUG_ON(!PageLocked(plaintext_page));
 
-	ctx = ext4_get_crypto_ctx(inode);
+	ctx = ext4_get_crypto_ctx(inode, gfp_flags);
 	if (IS_ERR(ctx))
 		return (struct page *) ctx;
 
 	/* The encryption operation will require a bounce page. */
-	ciphertext_page = alloc_bounce_page(ctx);
+	ciphertext_page = alloc_bounce_page(ctx, gfp_flags);
 	if (IS_ERR(ciphertext_page))
 		goto errout;
 	ctx->w.control_page = plaintext_page;
 	err = ext4_page_crypto(inode, EXT4_ENCRYPT, plaintext_page->index,
-			       plaintext_page, ciphertext_page);
+			       plaintext_page, ciphertext_page, gfp_flags);
 	if (err) {
 		ciphertext_page = ERR_PTR(err);
 	errout:
@@ -378,8 +382,8 @@ int ext4_decrypt(struct page *page)
 {
 	BUG_ON(!PageLocked(page));
 
-	return ext4_page_crypto(page->mapping->host,
-				EXT4_DECRYPT, page->index, page, page);
+	return ext4_page_crypto(page->mapping->host, EXT4_DECRYPT,
+				page->index, page, page, GFP_NOFS);
 }
 
 int ext4_encrypted_zeroout(struct inode *inode, ext4_lblk_t lblk,
@@ -398,11 +402,11 @@ int ext4_encrypted_zeroout(struct inode *inode, ext4_lblk_t lblk,
 
 	BUG_ON(inode->i_sb->s_blocksize != PAGE_CACHE_SIZE);
 
-	ctx = ext4_get_crypto_ctx(inode);
+	ctx = ext4_get_crypto_ctx(inode, GFP_NOFS);
 	if (IS_ERR(ctx))
 		return PTR_ERR(ctx);
 
-	ciphertext_page = alloc_bounce_page(ctx);
+	ciphertext_page = alloc_bounce_page(ctx, GFP_NOWAIT);
 	if (IS_ERR(ciphertext_page)) {
 		err = PTR_ERR(ciphertext_page);
 		goto errout;
@@ -410,11 +414,12 @@ int ext4_encrypted_zeroout(struct inode *inode, ext4_lblk_t lblk,
 
 	while (len--) {
 		err = ext4_page_crypto(inode, EXT4_ENCRYPT, lblk,
-				       ZERO_PAGE(0), ciphertext_page);
+				       ZERO_PAGE(0), ciphertext_page,
+				       GFP_NOFS);
 		if (err)
 			goto errout;
 
-		bio = bio_alloc(GFP_KERNEL, 1);
+		bio = bio_alloc(GFP_NOWAIT, 1);
 		if (!bio) {
 			err = -ENOMEM;
 			goto errout;

fs/ext4/ext4.h

@@ -2282,11 +2282,13 @@ extern struct kmem_cache *ext4_crypt_info_cachep;
 bool ext4_valid_contents_enc_mode(uint32_t mode);
 uint32_t ext4_validate_encryption_key_size(uint32_t mode, uint32_t size);
 extern struct workqueue_struct *ext4_read_workqueue;
-struct ext4_crypto_ctx *ext4_get_crypto_ctx(struct inode *inode);
+struct ext4_crypto_ctx *ext4_get_crypto_ctx(struct inode *inode,
+					    gfp_t gfp_flags);
 void ext4_release_crypto_ctx(struct ext4_crypto_ctx *ctx);
 void ext4_restore_control_page(struct page *data_page);
 struct page *ext4_encrypt(struct inode *inode,
-			  struct page *plaintext_page);
+			  struct page *plaintext_page,
+			  gfp_t gfp_flags);
 int ext4_decrypt(struct page *page);
 int ext4_encrypted_zeroout(struct inode *inode, ext4_lblk_t lblk,
 			   ext4_fsblk_t pblk, ext4_lblk_t len);

fs/ext4/page-io.c

@@ -23,6 +23,7 @@
 #include <linux/kernel.h>
 #include <linux/slab.h>
 #include <linux/mm.h>
+#include <linux/backing-dev.h>
 
 #include "ext4_jbd2.h"
 #include "xattr.h"
@@ -470,9 +471,20 @@ int ext4_bio_write_page(struct ext4_io_submit *io,
 
 	if (ext4_encrypted_inode(inode) && S_ISREG(inode->i_mode) &&
 	    nr_to_submit) {
-		data_page = ext4_encrypt(inode, page);
+		gfp_t gfp_flags = GFP_NOFS;
+
+	retry_encrypt:
+		data_page = ext4_encrypt(inode, page, gfp_flags);
 		if (IS_ERR(data_page)) {
 			ret = PTR_ERR(data_page);
+			if (ret == ENOMEM && wbc->sync_mode == WB_SYNC_ALL) {
+				if (io->io_bio) {
+					ext4_io_submit(io);
+					congestion_wait(BLK_RW_ASYNC, HZ/50);
+				}
+				gfp_flags |= __GFP_NOFAIL;
+				goto retry_encrypt;
+			}
 			data_page = NULL;
 			goto out;
 		}

fs/ext4/readpage.c

@@ -279,7 +279,7 @@ int ext4_mpage_readpages(struct address_space *mapping,
 
 			if (ext4_encrypted_inode(inode) &&
 			    S_ISREG(inode->i_mode)) {
-				ctx = ext4_get_crypto_ctx(inode);
+				ctx = ext4_get_crypto_ctx(inode, GFP_NOFS);
 				if (IS_ERR(ctx))
 					goto set_error_page;
 			}