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ext4: avoid deadlock in fs reclaim with page writeback

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Ext4 has a filesystem wide lock protecting ext4_writepages() calls to
avoid races with switching of journalled data flag or inode format. This
lock can however cause a deadlock like:

CPU0                            CPU1

ext4_writepages()
  percpu_down_read(sbi->s_writepages_rwsem);
                                ext4_change_inode_journal_flag()
                                  percpu_down_write(sbi->s_writepages_rwsem);
                                    - blocks, all readers block from now on
  ext4_do_writepages()
    ext4_init_io_end()
      kmem_cache_zalloc(io_end_cachep, GFP_KERNEL)
        fs_reclaim frees dentry...
          dentry_unlink_inode()
            iput() - last ref =>
              iput_final() - inode dirty =>
                write_inode_now()...
                  ext4_writepages() tries to acquire sbi->s_writepages_rwsem
                    and blocks forever

Make sure we cannot recurse into filesystem reclaim from writeback code
to avoid the deadlock.

Reported-by: syzbot+6898da502aef574c5f8a@syzkaller.appspotmail.com
Link: https://lore.kernel.org/all/0000000000004c66b405fa108e27@google.com
Fixes: c8585c6fca ("ext4: fix races between changing inode journal mode and ext4_writepages")
CC: stable@vger.kernel.org
Signed-off-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20230504124723.20205-1-jack@suse.cz
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
This commit is contained in:
Jan Kara
2023-05-04 14:47:23 +02:00
committed by Theodore Ts'o
parent b87c7cdf2b
commit 00d873c17e
3 changed files with 40 additions and 13 deletions
Download Patch File Download Diff File Expand all files Collapse all files

11
fs/ext4/migrate.c
View File

@ -408,7 +408,6 @@ static int free_ext_block(handle_t *handle, struct inode *inode)
int ext4_ext_migrate(struct inode *inode)
{
struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
handle_t *handle;
int retval = 0, i;
__le32 *i_data;
@ -418,6 +417,7 @@ int ext4_ext_migrate(struct inode *inode)
unsigned long max_entries;
__u32 goal, tmp_csum_seed;
uid_t owner[2];
int alloc_ctx;
/*
* If the filesystem does not support extents, or the inode
@ -434,7 +434,7 @@ int ext4_ext_migrate(struct inode *inode)
*/
return retval;
percpu_down_write(&sbi->s_writepages_rwsem);
alloc_ctx = ext4_writepages_down_write(inode->i_sb);
/*
* Worst case we can touch the allocation bitmaps and a block
@ -586,7 +586,7 @@ out_tmp_inode:
unlock_new_inode(tmp_inode);
iput(tmp_inode);
out_unlock:
percpu_up_write(&sbi->s_writepages_rwsem);
ext4_writepages_up_write(inode->i_sb, alloc_ctx);
return retval;
}
@ -605,6 +605,7 @@ int ext4_ind_migrate(struct inode *inode)
ext4_fsblk_t blk;
handle_t *handle;
int ret, ret2 = 0;
int alloc_ctx;
if (!ext4_has_feature_extents(inode->i_sb) ||
(!ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)))
@ -621,7 +622,7 @@ int ext4_ind_migrate(struct inode *inode)
if (test_opt(inode->i_sb, DELALLOC))
ext4_alloc_da_blocks(inode);
percpu_down_write(&sbi->s_writepages_rwsem);
alloc_ctx = ext4_writepages_down_write(inode->i_sb);
handle = ext4_journal_start(inode, EXT4_HT_MIGRATE, 1);
if (IS_ERR(handle)) {
@ -665,6 +666,6 @@ errout:
ext4_journal_stop(handle);
up_write(&EXT4_I(inode)->i_data_sem);
out_unlock:
percpu_up_write(&sbi->s_writepages_rwsem);
ext4_writepages_up_write(inode->i_sb, alloc_ctx);
return ret;
}