ext4: fix potential race between online resizing and write operations

[linux.git] / fs / ext4 / resize.c

diff --git a/fs/ext4/resize.c b/fs/ext4/resize.c
index 86a2500ed292f136b93f2ee75e71638567a72646..536cc9f380914316fe7ee0f4a46002190bf58979 100644 (file)
--- a/fs/ext4/resize.c
+++ b/fs/ext4/resize.c
@@ -17,6 +17,33 @@
 
 #include "ext4_jbd2.h"
 
+struct ext4_rcu_ptr {
+       struct rcu_head rcu;
+       void *ptr;
+};
+
+static void ext4_rcu_ptr_callback(struct rcu_head *head)
+{
+       struct ext4_rcu_ptr *ptr;
+
+       ptr = container_of(head, struct ext4_rcu_ptr, rcu);
+       kvfree(ptr->ptr);
+       kfree(ptr);
+}
+
+void ext4_kvfree_array_rcu(void *to_free)
+{
+       struct ext4_rcu_ptr *ptr = kzalloc(sizeof(*ptr), GFP_KERNEL);
+
+       if (ptr) {
+               ptr->ptr = to_free;
+               call_rcu(&ptr->rcu, ext4_rcu_ptr_callback);
+               return;
+       }
+       synchronize_rcu();
+       kvfree(to_free);
+}
+
 int ext4_resize_begin(struct super_block *sb)
 {
        struct ext4_sb_info *sbi = EXT4_SB(sb);
@@ -542,8 +569,8 @@ static int setup_new_flex_group_blocks(struct super_block *sb,
                                brelse(gdb);
                                goto out;
                        }
-                       memcpy(gdb->b_data, sbi->s_group_desc[j]->b_data,
-                              gdb->b_size);
+                       memcpy(gdb->b_data, sbi_array_rcu_deref(sbi,
+                               s_group_desc, j)->b_data, gdb->b_size);
                        set_buffer_uptodate(gdb);
 
                        err = ext4_handle_dirty_metadata(handle, NULL, gdb);
@@ -860,13 +887,15 @@ static int add_new_gdb(handle_t *handle, struct inode *inode,
        }
        brelse(dind);
 
-       o_group_desc = EXT4_SB(sb)->s_group_desc;
+       rcu_read_lock();
+       o_group_desc = rcu_dereference(EXT4_SB(sb)->s_group_desc);
        memcpy(n_group_desc, o_group_desc,
               EXT4_SB(sb)->s_gdb_count * sizeof(struct buffer_head *));
+       rcu_read_unlock();
        n_group_desc[gdb_num] = gdb_bh;
-       EXT4_SB(sb)->s_group_desc = n_group_desc;
+       rcu_assign_pointer(EXT4_SB(sb)->s_group_desc, n_group_desc);
        EXT4_SB(sb)->s_gdb_count++;
-       kvfree(o_group_desc);
+       ext4_kvfree_array_rcu(o_group_desc);
 
        le16_add_cpu(&es->s_reserved_gdt_blocks, -1);
        err = ext4_handle_dirty_super(handle, sb);
@@ -909,9 +938,11 @@ static int add_new_gdb_meta_bg(struct super_block *sb,
                return err;
        }
 
-       o_group_desc = EXT4_SB(sb)->s_group_desc;
+       rcu_read_lock();
+       o_group_desc = rcu_dereference(EXT4_SB(sb)->s_group_desc);
        memcpy(n_group_desc, o_group_desc,
               EXT4_SB(sb)->s_gdb_count * sizeof(struct buffer_head *));
+       rcu_read_unlock();
        n_group_desc[gdb_num] = gdb_bh;
 
        BUFFER_TRACE(gdb_bh, "get_write_access");
@@ -922,9 +953,9 @@ static int add_new_gdb_meta_bg(struct super_block *sb,
                return err;
        }
 
-       EXT4_SB(sb)->s_group_desc = n_group_desc;
+       rcu_assign_pointer(EXT4_SB(sb)->s_group_desc, n_group_desc);
        EXT4_SB(sb)->s_gdb_count++;
-       kvfree(o_group_desc);
+       ext4_kvfree_array_rcu(o_group_desc);
        return err;
 }
 
@@ -1188,7 +1219,8 @@ static int ext4_add_new_descs(handle_t *handle, struct super_block *sb,
                 * use non-sparse filesystems anymore.  This is already checked above.
                 */
                if (gdb_off) {
-                       gdb_bh = sbi->s_group_desc[gdb_num];
+                       gdb_bh = sbi_array_rcu_deref(sbi, s_group_desc,
+                                                    gdb_num);
                        BUFFER_TRACE(gdb_bh, "get_write_access");
                        err = ext4_journal_get_write_access(handle, gdb_bh);
 
@@ -1270,7 +1302,7 @@ static int ext4_setup_new_descs(handle_t *handle, struct super_block *sb,
                /*
                 * get_write_access() has been called on gdb_bh by ext4_add_new_desc().
                 */
-               gdb_bh = sbi->s_group_desc[gdb_num];
+               gdb_bh = sbi_array_rcu_deref(sbi, s_group_desc, gdb_num);
                /* Update group descriptor block for new group */
                gdp = (struct ext4_group_desc *)(gdb_bh->b_data +
                                                 gdb_off * EXT4_DESC_SIZE(sb));
@@ -1497,7 +1529,8 @@ static int ext4_flex_group_add(struct super_block *sb,
                for (; gdb_num <= gdb_num_end; gdb_num++) {
                        struct buffer_head *gdb_bh;
 
-                       gdb_bh = sbi->s_group_desc[gdb_num];
+                       gdb_bh = sbi_array_rcu_deref(sbi, s_group_desc,
+                                                    gdb_num);
                        if (old_gdb == gdb_bh->b_blocknr)
                                continue;
                        update_backups(sb, gdb_bh->b_blocknr, gdb_bh->b_data,