[PATCH] Handle high-order allocation failures in ubifs_jnl_write_data

[Matthew L. Creech]

Running kernel 2.6.37, my PPC-based device occasionally gets an
order-2 allocation failure in UBIFS, which causes the root FS to
become unwritable:

kswapd0: page allocation failure. order:2, mode:0x4050
Call Trace:
[c787dc30] [c00085b8] show_stack+0x7c/0x194 (unreliable)
[c787dc70] [c0061aec] __alloc_pages_nodemask+0x4f0/0x57c
[c787dd00] [c0061b98] __get_free_pages+0x20/0x50
[c787dd10] [c00e4f88] ubifs_jnl_write_data+0x54/0x200
[c787dd50] [c00e82d4] do_writepage+0x94/0x198
[c787dd90] [c00675e4] shrink_page_list+0x40c/0x77c
[c787de40] [c0067de0] shrink_inactive_list+0x1e0/0x370
[c787de90] [c0068224] shrink_zone+0x2b4/0x2b8
[c787df00] [c0068854] kswapd+0x408/0x5d4
[c787dfb0] [c0037bcc] kthread+0x80/0x84
[c787dff0] [c000ef44] kernel_thread+0x4c/0x68

Similar problems were encountered last April by Tomasz Stanislawski:

http://patchwork.ozlabs.org/patch/50965/

This patch implements Artem's suggested fix: fall back to a
mutex-protected static buffer, allocated at mount time.  I tested it
by forcing execution down the failure path, and didn't see any ill
effects.  Any feedback is appreciated, thanks!

Signed-off-by: Matthew L. Creech <mlcreech at gmail.com>
---
 fs/ubifs/journal.c |   24 +++++++++++++++++-------
 fs/ubifs/super.c   |    1 +
 fs/ubifs/ubifs.h   |   16 ++++++++++++++++
 3 files changed, 34 insertions(+), 7 deletions(-)

diff -purN orig/fs/ubifs/journal.c linux-2.6.37/fs/ubifs/journal.c
--- orig/fs/ubifs/journal.c	2011-03-04 15:44:41.568667187 -0500
+++ linux-2.6.37/fs/ubifs/journal.c	2011-03-04 17:28:01.878665040 -0500
@@ -689,8 +689,8 @@ int ubifs_jnl_write_data(struct ubifs_in
 			 const union ubifs_key *key, const void *buf, int len)
 {
 	struct ubifs_data_node *data;
-	int err, lnum, offs, compr_type, out_len;
-	int dlen = UBIFS_DATA_NODE_SZ + UBIFS_BLOCK_SIZE * WORST_COMPR_FACTOR;
+	int err, lnum, offs, compr_type, out_len, allocated = 1;
+	int dlen = UBIFS_JNL_DATA_NODE_SZ;
 	struct ubifs_inode *ui = ubifs_inode(inode);

 	dbg_jnl("ino %lu, blk %u, len %d, key %s",
@@ -698,9 +698,13 @@ int ubifs_jnl_write_data(struct ubifs_in
 		DBGKEY(key));
 	ubifs_assert(len <= UBIFS_BLOCK_SIZE);

-	data = kmalloc(dlen, GFP_NOFS);
-	if (!data)
-		return -ENOMEM;
+	data = kmalloc(dlen, GFP_NOFS | __GFP_NOWARN);
+	if (!data) {
+		/* If kmalloc() fails, fall back to using a shared buffer */
+		allocated = 0;
+		mutex_lock(&c->write_reserve_mutex);
+		data = &c->write_reserve.node;
+	}

 	data->ch.node_type = UBIFS_DATA_NODE;
 	key_write(c, key, &data->key);
@@ -736,7 +740,10 @@ int ubifs_jnl_write_data(struct ubifs_in
 		goto out_ro;

 	finish_reservation(c);
-	kfree(data);
+	if (!allocated)
+		mutex_unlock(&c->write_reserve_mutex);
+	else
+		kfree(data);
 	return 0;

 out_release:
@@ -745,7 +752,10 @@ out_ro:
 	ubifs_ro_mode(c, err);
 	finish_reservation(c);
 out_free:
-	kfree(data);
+	if (!allocated)
+		mutex_unlock(&c->write_reserve_mutex);
+	else
+		kfree(data);
 	return err;
 }

diff -purN orig/fs/ubifs/super.c linux-2.6.37/fs/ubifs/super.c
--- orig/fs/ubifs/super.c	2011-03-04 15:44:41.568667187 -0500
+++ linux-2.6.37/fs/ubifs/super.c	2011-03-04 16:56:35.628665311 -0500
@@ -1929,6 +1929,7 @@ static int ubifs_fill_super(struct super
 	mutex_init(&c->mst_mutex);
 	mutex_init(&c->umount_mutex);
 	mutex_init(&c->bu_mutex);
+	mutex_init(&c->write_reserve_mutex);
 	init_waitqueue_head(&c->cmt_wq);
 	c->buds = RB_ROOT;
 	c->old_idx = RB_ROOT;
diff -purN orig/fs/ubifs/ubifs.h linux-2.6.37/fs/ubifs/ubifs.h
--- orig/fs/ubifs/ubifs.h	2011-03-04 15:44:41.568667187 -0500
+++ linux-2.6.37/fs/ubifs/ubifs.h	2011-03-04 17:03:28.408664874 -0500
@@ -158,6 +158,19 @@
 #define UBIFS_MAX_BULK_READ 32

 /*
+ * How much space is needed for a single write buffer when writing out a
+ * journal data node.
+ */
+#define UBIFS_JNL_DATA_NODE_SZ \
+	(UBIFS_DATA_NODE_SZ + UBIFS_BLOCK_SIZE * WORST_COMPR_FACTOR)
+
+/* Used as a static buffer for journal writes, in case kmalloc() fails */
+union ubifs_write_reserve_buf {
+	struct ubifs_data_node node;
+	__u8 buf[UBIFS_JNL_DATA_NODE_SZ];
+};
+
+/*
  * Lockdep classes for UBIFS inode @ui_mutex.
  */
 enum {
@@ -1249,6 +1262,9 @@ struct ubifs_info {
 	int max_bu_buf_len;
 	struct mutex bu_mutex;
 	struct bu_info bu;
+	
+	struct mutex write_reserve_mutex;
+	union ubifs_write_reserve_buf write_reserve;

 	int log_lebs;
 	long long log_bytes;

-- 
Matthew L. Creech