ext4: avoid deadlock in fs reclaim with page writeback

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: ext4: avoid deadlock in fs reclaim with page writeback 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.

References

• https://git.kernel.org/stable/c/2ec97dc90df40c50e509809dc9a198638a7e18b6
• https://git.kernel.org/stable/c/4b4340bf04ce9a52061f15000ecedd126abc093c
• https://git.kernel.org/stable/c/00d873c17e29cc32d90ca852b82685f1673acaa5