UBIFS: handle allocation failures in UBIFS write path

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.

Artem: massaged the patch a little, improved it so that we'd not
allocate the write reserve buffer when we are in R/O mode.

Signed-off-by: Matthew L. Creech <mlcreech@gmail.com>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>

1 files changed, 18 insertions, 0 deletions

diff --git a/fs/ubifs/super.c b/fs/ubifs/super.c
index d4b4cb4596e2..e360c7a71f9e 100644
--- a/fs/ubifs/super.c
+++ b/fs/ubifs/super.c
@@ -1213,6 +1213,13 @@ static int mount_ubifs(struct ubifs_info *c)
 	if (c->bulk_read == 1)
 		bu_init(c);
 
+	if (!c->ro_mount) {
+		c->write_reserve_buf = kmalloc(COMPRESSED_DATA_NODE_BUF_SZ,
+					       GFP_KERNEL);
+		if (!c->write_reserve_buf)
+			goto out_free;
+	}
+
 	c->mounting = 1;
 
 	err = ubifs_read_superblock(c);
@@ -1482,6 +1489,7 @@ out_wbufs:
 out_cbuf:
 	kfree(c->cbuf);
 out_free:
+	kfree(c->write_reserve_buf);
 	kfree(c->bu.buf);
 	vfree(c->ileb_buf);
 	vfree(c->sbuf);
@@ -1520,6 +1528,7 @@ static void ubifs_umount(struct ubifs_info *c)
 	kfree(c->cbuf);
 	kfree(c->rcvrd_mst_node);
 	kfree(c->mst_node);
+	kfree(c->write_reserve_buf);
 	kfree(c->bu.buf);
 	vfree(c->ileb_buf);
 	vfree(c->sbuf);
@@ -1605,6 +1614,10 @@ static int ubifs_remount_rw(struct ubifs_info *c)
 		goto out;
 	}
 
+	c->write_reserve_buf = kmalloc(COMPRESSED_DATA_NODE_BUF_SZ, GFP_KERNEL);
+	if (!c->write_reserve_buf)
+		goto out;
+
 	err = ubifs_lpt_init(c, 0, 1);
 	if (err)
 		goto out;
@@ -1669,6 +1682,8 @@ out:
 		c->bgt = NULL;
 	}
 	free_wbufs(c);
+	kfree(c->write_reserve_buf);
+	c->write_reserve_buf = NULL;
 	vfree(c->ileb_buf);
 	c->ileb_buf = NULL;
 	ubifs_lpt_free(c, 1);
@@ -1712,6 +1727,8 @@ static void ubifs_remount_ro(struct ubifs_info *c)
 	free_wbufs(c);
 	vfree(c->orph_buf);
 	c->orph_buf = NULL;
+	kfree(c->write_reserve_buf);
+	c->write_reserve_buf = NULL;
 	vfree(c->ileb_buf);
 	c->ileb_buf = NULL;
 	ubifs_lpt_free(c, 1);
@@ -1942,6 +1959,7 @@ static int ubifs_fill_super(struct super_block *sb, void *data, int silent)
 	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;