ext4: fix race when setting bitmap_uptodate flag
In ext4_read_{inode,block}_bitmap() we were setting bitmap_uptodate()
before submitting the buffer for read. The is bad, since we check
bitmap_uptodate() without locking the buffer, and so if another
process is racing with us, it's possible that they will think the
bitmap is uptodate even though the read has not completed yet,
resulting in inodes and blocks potentially getting allocated more than
once if we get really unlucky.
Addresses-Google-Bug: 2828254
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c
index f9e2cd8..a2cff2b 100644
--- a/fs/ext4/balloc.c
+++ b/fs/ext4/balloc.c
@@ -336,10 +336,10 @@
* Return buffer_head on success or NULL in case of failure.
*/
struct buffer_head *
-ext4_read_block_bitmap(struct super_block *sb, ext4_group_t block_group)
+ext4_read_block_bitmap_nowait(struct super_block *sb, ext4_group_t block_group)
{
struct ext4_group_desc *desc;
- struct buffer_head *bh = NULL;
+ struct buffer_head *bh;
ext4_fsblk_t bitmap_blk;
desc = ext4_get_group_desc(sb, block_group, NULL);
@@ -348,9 +348,9 @@
bitmap_blk = ext4_block_bitmap(sb, desc);
bh = sb_getblk(sb, bitmap_blk);
if (unlikely(!bh)) {
- ext4_error(sb, "Cannot read block bitmap - "
- "block_group = %u, block_bitmap = %llu",
- block_group, bitmap_blk);
+ ext4_error(sb, "Cannot get buffer for block bitmap - "
+ "block_group = %u, block_bitmap = %llu",
+ block_group, bitmap_blk);
return NULL;
}
@@ -382,25 +382,50 @@
return bh;
}
/*
- * submit the buffer_head for read. We can
- * safely mark the bitmap as uptodate now.
- * We do it here so the bitmap uptodate bit
- * get set with buffer lock held.
+ * submit the buffer_head for reading
*/
+ set_buffer_new(bh);
trace_ext4_read_block_bitmap_load(sb, block_group);
- set_bitmap_uptodate(bh);
- if (bh_submit_read(bh) < 0) {
- put_bh(bh);
+ bh->b_end_io = ext4_end_bitmap_read;
+ get_bh(bh);
+ submit_bh(READ, bh);
+ return bh;
+}
+
+/* Returns 0 on success, 1 on error */
+int ext4_wait_block_bitmap(struct super_block *sb, ext4_group_t block_group,
+ struct buffer_head *bh)
+{
+ struct ext4_group_desc *desc;
+
+ if (!buffer_new(bh))
+ return 0;
+ desc = ext4_get_group_desc(sb, block_group, NULL);
+ if (!desc)
+ return 1;
+ wait_on_buffer(bh);
+ if (!buffer_uptodate(bh)) {
ext4_error(sb, "Cannot read block bitmap - "
- "block_group = %u, block_bitmap = %llu",
- block_group, bitmap_blk);
+ "block_group = %u, block_bitmap = %llu",
+ block_group, bh->b_blocknr);
+ return 1;
+ }
+ clear_buffer_new(bh);
+ /* Panic or remount fs read-only if block bitmap is invalid */
+ ext4_valid_block_bitmap(sb, desc, block_group, bh);
+ return 0;
+}
+
+struct buffer_head *
+ext4_read_block_bitmap(struct super_block *sb, ext4_group_t block_group)
+{
+ struct buffer_head *bh;
+
+ bh = ext4_read_block_bitmap_nowait(sb, block_group);
+ if (ext4_wait_block_bitmap(sb, block_group, bh)) {
+ put_bh(bh);
return NULL;
}
- ext4_valid_block_bitmap(sb, desc, block_group, bh);
- /*
- * file system mounted not to panic on error,
- * continue with corrupt bitmap
- */
return bh;
}
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 513004f..315f01b 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1794,8 +1794,14 @@
ext4_group_t block_group,
struct buffer_head ** bh);
extern int ext4_should_retry_alloc(struct super_block *sb, int *retries);
-struct buffer_head *ext4_read_block_bitmap(struct super_block *sb,
- ext4_group_t block_group);
+
+extern struct buffer_head *ext4_read_block_bitmap_nowait(struct super_block *sb,
+ ext4_group_t block_group);
+extern int ext4_wait_block_bitmap(struct super_block *sb,
+ ext4_group_t block_group,
+ struct buffer_head *bh);
+extern struct buffer_head *ext4_read_block_bitmap(struct super_block *sb,
+ ext4_group_t block_group);
extern void ext4_init_block_bitmap(struct super_block *sb,
struct buffer_head *bh,
ext4_group_t group,
@@ -1841,6 +1847,7 @@
extern void ext4_mark_bitmap_end(int start_bit, int end_bit, char *bitmap);
extern int ext4_init_inode_table(struct super_block *sb,
ext4_group_t group, int barrier);
+extern void ext4_end_bitmap_read(struct buffer_head *bh, int uptodate);
/* mballoc.c */
extern long ext4_mb_stats;
diff --git a/fs/ext4/ialloc.c b/fs/ext4/ialloc.c
index 84e6e9a..b268599 100644
--- a/fs/ext4/ialloc.c
+++ b/fs/ext4/ialloc.c
@@ -92,6 +92,16 @@
return EXT4_INODES_PER_GROUP(sb);
}
+void ext4_end_bitmap_read(struct buffer_head *bh, int uptodate)
+{
+ if (uptodate) {
+ set_buffer_uptodate(bh);
+ set_bitmap_uptodate(bh);
+ }
+ unlock_buffer(bh);
+ put_bh(bh);
+}
+
/*
* Read the inode allocation bitmap for a given block_group, reading
* into the specified slot in the superblock's bitmap cache.
@@ -147,18 +157,18 @@
return bh;
}
/*
- * submit the buffer_head for read. We can
- * safely mark the bitmap as uptodate now.
- * We do it here so the bitmap uptodate bit
- * get set with buffer lock held.
+ * submit the buffer_head for reading
*/
trace_ext4_load_inode_bitmap(sb, block_group);
- set_bitmap_uptodate(bh);
- if (bh_submit_read(bh) < 0) {
+ bh->b_end_io = ext4_end_bitmap_read;
+ get_bh(bh);
+ submit_bh(READ, bh);
+ wait_on_buffer(bh);
+ if (!buffer_uptodate(bh)) {
put_bh(bh);
ext4_error(sb, "Cannot read inode bitmap - "
- "block_group = %u, inode_bitmap = %llu",
- block_group, bitmap_blk);
+ "block_group = %u, inode_bitmap = %llu",
+ block_group, bitmap_blk);
return NULL;
}
return bh;
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index cb990b2..545fa02 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -782,7 +782,7 @@
int groups_per_page;
int err = 0;
int i;
- ext4_group_t first_group;
+ ext4_group_t first_group, group;
int first_block;
struct super_block *sb;
struct buffer_head *bhs;
@@ -806,24 +806,23 @@
/* allocate buffer_heads to read bitmaps */
if (groups_per_page > 1) {
- err = -ENOMEM;
i = sizeof(struct buffer_head *) * groups_per_page;
bh = kzalloc(i, GFP_NOFS);
- if (bh == NULL)
+ if (bh == NULL) {
+ err = -ENOMEM;
goto out;
+ }
} else
bh = &bhs;
first_group = page->index * blocks_per_page / 2;
/* read all groups the page covers into the cache */
- for (i = 0; i < groups_per_page; i++) {
- struct ext4_group_desc *desc;
-
- if (first_group + i >= ngroups)
+ for (i = 0, group = first_group; i < groups_per_page; i++, group++) {
+ if (group >= ngroups)
break;
- grinfo = ext4_get_group_info(sb, first_group + i);
+ grinfo = ext4_get_group_info(sb, group);
/*
* If page is uptodate then we came here after online resize
* which added some new uninitialized group info structs, so
@@ -834,69 +833,21 @@
bh[i] = NULL;
continue;
}
-
- err = -EIO;
- desc = ext4_get_group_desc(sb, first_group + i, NULL);
- if (desc == NULL)
+ if (!(bh[i] = ext4_read_block_bitmap_nowait(sb, group))) {
+ err = -ENOMEM;
goto out;
-
- err = -ENOMEM;
- bh[i] = sb_getblk(sb, ext4_block_bitmap(sb, desc));
- if (bh[i] == NULL)
- goto out;
-
- if (bitmap_uptodate(bh[i]))
- continue;
-
- lock_buffer(bh[i]);
- if (bitmap_uptodate(bh[i])) {
- unlock_buffer(bh[i]);
- continue;
}
- ext4_lock_group(sb, first_group + i);
- if (desc->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT)) {
- ext4_init_block_bitmap(sb, bh[i],
- first_group + i, desc);
- set_bitmap_uptodate(bh[i]);
- set_buffer_uptodate(bh[i]);
- ext4_unlock_group(sb, first_group + i);
- unlock_buffer(bh[i]);
- continue;
- }
- ext4_unlock_group(sb, first_group + i);
- if (buffer_uptodate(bh[i])) {
- /*
- * if not uninit if bh is uptodate,
- * bitmap is also uptodate
- */
- set_bitmap_uptodate(bh[i]);
- unlock_buffer(bh[i]);
- continue;
- }
- get_bh(bh[i]);
- /*
- * submit the buffer_head for read. We can
- * safely mark the bitmap as uptodate now.
- * We do it here so the bitmap uptodate bit
- * get set with buffer lock held.
- */
- set_bitmap_uptodate(bh[i]);
- bh[i]->b_end_io = end_buffer_read_sync;
- submit_bh(READ, bh[i]);
- mb_debug(1, "read bitmap for group %u\n", first_group + i);
+ mb_debug(1, "read bitmap for group %u\n", group);
}
/* wait for I/O completion */
- for (i = 0; i < groups_per_page; i++)
- if (bh[i])
- wait_on_buffer(bh[i]);
-
- err = -EIO;
- for (i = 0; i < groups_per_page; i++)
- if (bh[i] && !buffer_uptodate(bh[i]))
+ for (i = 0, group = first_group; i < groups_per_page; i++, group++) {
+ if (bh[i] && ext4_wait_block_bitmap(sb, group, bh[i])) {
+ err = -EIO;
goto out;
+ }
+ }
- err = 0;
first_block = page->index * blocks_per_page;
for (i = 0; i < blocks_per_page; i++) {
int group;