• R
    CIFS: fix circular locking dependency · 966681c9
    Rabin Vincent 提交于
    When a CIFS filesystem is mounted with the forcemand option and the
    following command is run on it, lockdep warns about a circular locking
    dependency between CifsInodeInfo::lock_sem and the inode lock.
    
     while echo foo > hello; do :; done & while touch -c hello; do :; done
    
    cifs_writev() takes the locks in the wrong order, but note that we can't
    only flip the order around because it releases the inode lock before the
    call to generic_write_sync() while it holds the lock_sem across that
    call.
    
    But, AFAICS, there is no need to hold the CifsInodeInfo::lock_sem across
    the generic_write_sync() call either, so we can release both the locks
    before generic_write_sync(), and change the order.
    
     ======================================================
     WARNING: possible circular locking dependency detected
     4.12.0-rc7+ #9 Not tainted
     ------------------------------------------------------
     touch/487 is trying to acquire lock:
      (&cifsi->lock_sem){++++..}, at: cifsFileInfo_put+0x88f/0x16a0
    
     but task is already holding lock:
      (&sb->s_type->i_mutex_key#11){+.+.+.}, at: utimes_common+0x3ad/0x870
    
     which lock already depends on the new lock.
    
     the existing dependency chain (in reverse order) is:
    
     -> #1 (&sb->s_type->i_mutex_key#11){+.+.+.}:
            __lock_acquire+0x1f74/0x38f0
            lock_acquire+0x1cc/0x600
            down_write+0x74/0x110
            cifs_strict_writev+0x3cb/0x8c0
            __vfs_write+0x4c1/0x930
            vfs_write+0x14c/0x2d0
            SyS_write+0xf7/0x240
            entry_SYSCALL_64_fastpath+0x1f/0xbe
    
     -> #0 (&cifsi->lock_sem){++++..}:
            check_prevs_add+0xfa0/0x1d10
            __lock_acquire+0x1f74/0x38f0
            lock_acquire+0x1cc/0x600
            down_write+0x74/0x110
            cifsFileInfo_put+0x88f/0x16a0
            cifs_setattr+0x992/0x1680
            notify_change+0x61a/0xa80
            utimes_common+0x3d4/0x870
            do_utimes+0x1c1/0x220
            SyS_utimensat+0x84/0x1a0
            entry_SYSCALL_64_fastpath+0x1f/0xbe
    
     other info that might help us debug this:
    
      Possible unsafe locking scenario:
    
            CPU0                    CPU1
            ----                    ----
       lock(&sb->s_type->i_mutex_key#11);
                                    lock(&cifsi->lock_sem);
                                    lock(&sb->s_type->i_mutex_key#11);
       lock(&cifsi->lock_sem);
    
      *** DEADLOCK ***
    
     2 locks held by touch/487:
      #0:  (sb_writers#10){.+.+.+}, at: mnt_want_write+0x41/0xb0
      #1:  (&sb->s_type->i_mutex_key#11){+.+.+.}, at: utimes_common+0x3ad/0x870
    
     stack backtrace:
     CPU: 0 PID: 487 Comm: touch Not tainted 4.12.0-rc7+ #9
     Call Trace:
      dump_stack+0xdb/0x185
      print_circular_bug+0x45b/0x790
      __lock_acquire+0x1f74/0x38f0
      lock_acquire+0x1cc/0x600
      down_write+0x74/0x110
      cifsFileInfo_put+0x88f/0x16a0
      cifs_setattr+0x992/0x1680
      notify_change+0x61a/0xa80
      utimes_common+0x3d4/0x870
      do_utimes+0x1c1/0x220
      SyS_utimensat+0x84/0x1a0
      entry_SYSCALL_64_fastpath+0x1f/0xbe
    
    Fixes: 19dfc1f5 ("cifs: fix the race in cifs_writev()")
    Signed-off-by: NRabin Vincent <rabinv@axis.com>
    Signed-off-by: NSteve French <smfrench@gmail.com>
    Acked-by: NPavel Shilovsky <pshilov@microsoft.com>
    966681c9
file.c 105.9 KB