We need some sort of synchronization while updating ->s_group_desc because there
are a lot of users which can access old ->s_group_desc array after it was released.
It is reasonable to use lightweight seqcount_t here instead of RCU.
Signed-off-by: Dmitry Monakhov <dmonakhov@xxxxxxxxxx>
---
fs/ext4/balloc.c | 14 ++++++++++----
fs/ext4/ext4.h | 1 +
fs/ext4/resize.c | 5 ++++-
fs/ext4/super.c | 1 +
4 files changed, 16 insertions(+), 5 deletions(-)
diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c
index 83a6f49..4746907 100644
--- a/fs/ext4/balloc.c
+++ b/fs/ext4/balloc.c
@@ -280,8 +280,10 @@ struct ext4_group_desc * ext4_get_group_desc(struct super_block *sb,
{
unsigned int group_desc;
unsigned int offset;
+ unsigned int seq;
ext4_group_t ngroups = ext4_get_groups_count(sb);
struct ext4_group_desc *desc;
+ struct buffer_head *gd_bh;
struct ext4_sb_info *sbi = EXT4_SB(sb);
if (block_group >= ngroups) {
@@ -293,7 +295,11 @@ struct ext4_group_desc * ext4_get_group_desc(struct super_block *sb,
group_desc = block_group >> EXT4_DESC_PER_BLOCK_BITS(sb);
offset = block_group & (EXT4_DESC_PER_BLOCK(sb) - 1);
- if (!sbi->s_group_desc[group_desc]) {
+ do {
+ seq = read_seqcount_begin(&sbi->s_group_desc_seq);
+ gd_bh = sbi->s_group_desc[group_desc];
+ } while (unlikely(read_seqcount_retry(&sbi->s_group_desc_seq, seq)));
+ if (!gd_bh) {
ext4_error(sb, "Group descriptor not loaded - "
"block_group = %u, group_desc = %u, desc = %u",
block_group, group_desc, offset);
@@ -301,10 +307,10 @@ struct ext4_group_desc * ext4_get_group_desc(struct super_block *sb,
}
desc = (struct ext4_group_desc *)(
- (__u8 *)sbi->s_group_desc[group_desc]->b_data +
- offset * EXT4_DESC_SIZE(sb));
+ (__u8 *)gd_bh->b_data + offset * EXT4_DESC_SIZE(sb));
if (bh)
- *bh = sbi->s_group_desc[group_desc];
+ *bh = gd_bh;
+
return desc;
}
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index c55a1fa..2c039d2 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1199,6 +1199,7 @@ struct ext4_sb_info {
struct buffer_head * s_sbh; /* Buffer containing the super block */
struct ext4_super_block *s_es; /* Pointer to the super block in the buffer */
struct buffer_head **s_group_desc;
+ seqcount_t s_group_desc_seq; /* protects s_group_desc updates */
unsigned int s_mount_opt;
unsigned int s_mount_opt2;
unsigned int s_mount_flags;
diff --git a/fs/ext4/resize.c b/fs/ext4/resize.c
index ca45883..f9ec935 100644
--- a/fs/ext4/resize.c
+++ b/fs/ext4/resize.c
@@ -854,8 +854,10 @@ static int add_new_gdb(handle_t *handle, struct inode *inode,
memcpy(n_group_desc, o_group_desc,
EXT4_SB(sb)->s_gdb_count * sizeof(struct buffer_head *));
n_group_desc[gdb_num] = gdb_bh;
+ write_seqcount_begin(&EXT4_SB(sb)->s_group_desc_seq);
EXT4_SB(sb)->s_group_desc = n_group_desc;
EXT4_SB(sb)->s_gdb_count++;
+ write_seqcount_end(&EXT4_SB(sb)->s_group_desc_seq);
ext4_kvfree(o_group_desc);
le16_add_cpu(&es->s_reserved_gdt_blocks, -1);
@@ -902,13 +904,14 @@ static int add_new_gdb_meta_bg(struct super_block *sb,
gdb_num + 1);
return err;
}
-
o_group_desc = EXT4_SB(sb)->s_group_desc;
memcpy(n_group_desc, o_group_desc,
EXT4_SB(sb)->s_gdb_count * sizeof(struct buffer_head *));
n_group_desc[gdb_num] = gdb_bh;
+ write_seqcount_begin(&EXT4_SB(sb)->s_group_desc_seq);
EXT4_SB(sb)->s_group_desc = n_group_desc;
EXT4_SB(sb)->s_gdb_count++;
+ write_seqcount_end(&EXT4_SB(sb)->s_group_desc_seq);
ext4_kvfree(o_group_desc);
BUFFER_TRACE(gdb_bh, "get_write_access");
err = ext4_journal_get_write_access(handle, gdb_bh);
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 5f6cab8..722e537 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -3872,6 +3872,7 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
(EXT4_MAX_BLOCK_FILE_PHYS / EXT4_BLOCKS_PER_GROUP(sb)));
db_count = (sbi->s_groups_count + EXT4_DESC_PER_BLOCK(sb) - 1) /
EXT4_DESC_PER_BLOCK(sb);
+ seqcount_init(&sbi->s_group_desc_seq);
sbi->s_group_desc = ext4_kvmalloc(db_count *
sizeof(struct buffer_head *),
GFP_KERNEL);
--
1.7.1
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