• Qian Cai's avatar
    ext4: fix a data race in EXT4_I(inode)->i_disksize · 35df4299
    Qian Cai authored
    EXT4_I(inode)->i_disksize could be accessed concurrently as noticed by
    KCSAN,
    
     BUG: KCSAN: data-race in ext4_write_end [ext4] / ext4_writepages [ext4]
    
     write to 0xffff91c6713b00f8 of 8 bytes by task 49268 on cpu 127:
      ext4_write_end+0x4e3/0x750 [ext4]
      ext4_update_i_disksize at fs/ext4/ext4.h:3032
      (inlined by) ext4_update_inode_size at fs/ext4/ext4.h:3046
      (inlined by) ext4_write_end at fs/ext4/inode.c:1287
      generic_perform_write+0x208/0x2a0
      ext4_buffered_write_iter+0x11f/0x210 [ext4]
      ext4_file_write_iter+0xce/0x9e0 [ext4]
      new_sync_write+0x29c/0x3b0
      __vfs_write+0x92/0xa0
      vfs_write+0x103/0x260
      ksys_write+0x9d/0x130
      __x64_sys_write+0x4c/0x60
      do_syscall_64+0x91/0xb47
      entry_SYSCALL_64_after_hwframe+0x49/0xbe
    
     read to 0xffff91c6713b00f8 of 8 bytes by task 24872 on cpu 37:
      ext4_writepages+0x10ac/0x1d00 [ext4]
      mpage_map_and_submit_extent at fs/ext4/inode.c:2468
      (inlined by) ext4_writepages at fs/ext4/inode.c:2772
      do_writepages+0x5e/0x130
      __writeback_single_inode+0xeb/0xb20
      writeback_sb_inodes+0x429/0x900
      __writeback_inodes_wb+0xc4/0x150
      wb_writeback+0x4bd/0x870
      wb_workfn+0x6b4/0x960
      process_one_work+0x54c/0xbe0
      worker_thread+0x80/0x650
      kthread+0x1e0/0x200
      ret_from_fork+0x27/0x50
    
     Reported by Kernel Concurrency Sanitizer on:
     CPU: 37 PID: 24872 Comm: kworker/u261:2 Tainted: G        W  O L 5.5.0-next-20200204+ #5
     Hardware name: HPE ProLiant DL385 Gen10/ProLiant DL385 Gen10, BIOS A40 07/10/2019
     Workqueue: writeback wb_workfn (flush-7:0)
    
    Since only the read is operating as lockless (outside of the
    "i_data_sem"), load tearing could introduce a logic bug. Fix it by
    adding READ_ONCE() for the read and WRITE_ONCE() for the write.
    Signed-off-by: default avatarQian Cai <cai@lca.pw>
    Link: https://lore.kernel.org/r/1581085751-31793-1-git-send-email-cai@lca.pwSigned-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
    Cc: stable@kernel.org
    35df4299
ext4.h 120 KB