On Tue, 29 Jul 2025 11:06:35 +0100, Al Viro wrote: syzbot reports data-race in fat32_ent_get/fat32_ent_put. CPU0(Task A) CPU1(Task B) ==== ==== vfs_write new_sync_write generic_file_write_iter fat_write_begin block_write_begin fat_get_block vfs_statfs fat_add_cluster statfs_by_dentry fat_chain_add fat_statfs fat_ent_write fat_count_free_clusters fat32_ent_put fat32_ent_get In fat_add_cluster(), fat_alloc_clusters() retrieves an free cluster and marks the entry with a value of FAT_ENT_EOF, protected by lock_fat(). There is no lock protection in fat_chain_add(). When fat_ent_write() writes the last entry to new_dclus, this has no effect on fat_count_free_clusters() in the statfs operation. The last entry is not FAT_ENT_FREE before or after the write. Therefore, the race condition reported here is invalid. BR, Edward
