ext4: Fix race between migration and mmap write
Fail migrate if we allocated new blocks via mmap write. If we write to holes in the file via mmap, we end up allocating new blocks. This block allocation happens without taking inode->i_mutex. Since migrate is protected by i_mutex and migrate expects that no new blocks get allocated during migrate, fail migrate if new blocks get allocated. We can't take inode->i_mutex in the mmap write path because that would result in a locking order violation between i_mutex and mmap_sem. Also adding a separate rw_sempahore for protection is really high overhead for a rare operation such as migrate. Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com> Acked-by: Jan Kara <jack@suse.cz> Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
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