• Tejun Heo's avatar
    kernfs: cache atomic_write_len in kernfs_open_file · b7ce40cf
    Tejun Heo authored
    While implementing atomic_write_len, 4d3773c4 ("kernfs: implement
    kernfs_ops->atomic_write_len") moved data copy from userland inside
    kernfs_get_active() and kernfs_open_file->mutex so that
    kernfs_ops->atomic_write_len can be accessed before copying buffer
    from userland; unfortunately, this could lead to locking order
    inversion involving mmap_sem if copy_from_user() takes a page fault.
    
      ======================================================
      [ INFO: possible circular locking dependency detected ]
      3.14.0-rc4-next-20140228-sasha-00011-g4077c67-dirty #26 Tainted: G        W
      -------------------------------------------------------
      trinity-c236/10658 is trying to acquire lock:
       (&of->mutex#2){+.+.+.}, at: [<fs/kernfs/file.c:487>] kernfs_fop_mmap+0x54/0x120
    
      but task is already holding lock:
       (&mm->mmap_sem){++++++}, at: [<mm/util.c:397>] vm_mmap_pgoff+0x6e/0xe0
    
      which lock already depends on the new lock.
    
      the existing dependency chain (in reverse order) is:
    
     -> #1 (&mm->mmap_sem){++++++}:
    	 [<kernel/locking/lockdep.c:1945 kernel/locking/lockdep.c:2131>] validate_chain+0x6c5/0x7b0
    	 [<kernel/locking/lockdep.c:3182>] __lock_acquire+0x4cd/0x5a0
    	 [<arch/x86/include/asm/current.h:14 kernel/locking/lockdep.c:3602>] lock_acquire+0x182/0x1d0
    	 [<mm/memory.c:4188>] might_fault+0x7e/0xb0
    	 [<arch/x86/include/asm/uaccess.h:713 fs/kernfs/file.c:291>] kernfs_fop_write+0xd8/0x190
    	 [<fs/read_write.c:473>] vfs_write+0xe3/0x1d0
    	 [<fs/read_write.c:523 fs/read_write.c:515>] SyS_write+0x5d/0xa0
    	 [<arch/x86/kernel/entry_64.S:749>] tracesys+0xdd/0xe2
    
     -> #0 (&of->mutex#2){+.+.+.}:
    	 [<kernel/locking/lockdep.c:1840>] check_prev_add+0x13f/0x560
    	 [<kernel/locking/lockdep.c:1945 kernel/locking/lockdep.c:2131>] validate_chain+0x6c5/0x7b0
    	 [<kernel/locking/lockdep.c:3182>] __lock_acquire+0x4cd/0x5a0
    	 [<arch/x86/include/asm/current.h:14 kernel/locking/lockdep.c:3602>] lock_acquire+0x182/0x1d0
    	 [<kernel/locking/mutex.c:470 kernel/locking/mutex.c:571>] mutex_lock_nested+0x6a/0x510
    	 [<fs/kernfs/file.c:487>] kernfs_fop_mmap+0x54/0x120
    	 [<mm/mmap.c:1573>] mmap_region+0x310/0x5c0
    	 [<mm/mmap.c:1365>] do_mmap_pgoff+0x385/0x430
    	 [<mm/util.c:399>] vm_mmap_pgoff+0x8f/0xe0
    	 [<mm/mmap.c:1416 mm/mmap.c:1374>] SyS_mmap_pgoff+0x1b0/0x210
    	 [<arch/x86/kernel/sys_x86_64.c:72>] SyS_mmap+0x1d/0x20
    	 [<arch/x86/kernel/entry_64.S:749>] tracesys+0xdd/0xe2
    
      other info that might help us debug this:
    
       Possible unsafe locking scenario:
    
    	 CPU0                    CPU1
    	 ----                    ----
        lock(&mm->mmap_sem);
    				 lock(&of->mutex#2);
    				 lock(&mm->mmap_sem);
        lock(&of->mutex#2);
    
       *** DEADLOCK ***
    
      1 lock held by trinity-c236/10658:
       #0:  (&mm->mmap_sem){++++++}, at: [<mm/util.c:397>] vm_mmap_pgoff+0x6e/0xe0
    
      stack backtrace:
      CPU: 2 PID: 10658 Comm: trinity-c236 Tainted: G        W 3.14.0-rc4-next-20140228-sasha-00011-g4077c67-dirty #26
       0000000000000000 ffff88011911fa48 ffffffff8438e945 0000000000000000
       0000000000000000 ffff88011911fa98 ffffffff811a0109 ffff88011911fab8
       ffff88011911fab8 ffff88011911fa98 ffff880119128cc0 ffff880119128cf8
      Call Trace:
       [<lib/dump_stack.c:52>] dump_stack+0x52/0x7f
       [<kernel/locking/lockdep.c:1213>] print_circular_bug+0x129/0x160
       [<kernel/locking/lockdep.c:1840>] check_prev_add+0x13f/0x560
       [<include/linux/spinlock.h:343 mm/slub.c:1933>] ? deactivate_slab+0x511/0x550
       [<kernel/locking/lockdep.c:1945 kernel/locking/lockdep.c:2131>] validate_chain+0x6c5/0x7b0
       [<kernel/locking/lockdep.c:3182>] __lock_acquire+0x4cd/0x5a0
       [<mm/mmap.c:1552>] ? mmap_region+0x24a/0x5c0
       [<arch/x86/include/asm/current.h:14 kernel/locking/lockdep.c:3602>] lock_acquire+0x182/0x1d0
       [<fs/kernfs/file.c:487>] ? kernfs_fop_mmap+0x54/0x120
       [<kernel/locking/mutex.c:470 kernel/locking/mutex.c:571>] mutex_lock_nested+0x6a/0x510
       [<fs/kernfs/file.c:487>] ? kernfs_fop_mmap+0x54/0x120
       [<kernel/sched/core.c:2477>] ? get_parent_ip+0x11/0x50
       [<fs/kernfs/file.c:487>] ? kernfs_fop_mmap+0x54/0x120
       [<fs/kernfs/file.c:487>] kernfs_fop_mmap+0x54/0x120
       [<mm/mmap.c:1573>] mmap_region+0x310/0x5c0
       [<mm/mmap.c:1365>] do_mmap_pgoff+0x385/0x430
       [<mm/util.c:397>] ? vm_mmap_pgoff+0x6e/0xe0
       [<mm/util.c:399>] vm_mmap_pgoff+0x8f/0xe0
       [<kernel/rcu/update.c:97>] ? __rcu_read_unlock+0x44/0xb0
       [<fs/file.c:641>] ? dup_fd+0x3c0/0x3c0
       [<mm/mmap.c:1416 mm/mmap.c:1374>] SyS_mmap_pgoff+0x1b0/0x210
       [<arch/x86/kernel/sys_x86_64.c:72>] SyS_mmap+0x1d/0x20
       [<arch/x86/kernel/entry_64.S:749>] tracesys+0xdd/0xe2
    
    Fix it by caching atomic_write_len in kernfs_open_file during open so
    that it can be determined without accessing kernfs_ops in
    kernfs_fop_write().  This restores the structure of kernfs_fop_write()
    before 4d3773c4 with updated @len determination logic.
    Signed-off-by: default avatarTejun Heo <tj@kernel.org>
    Reported-by: default avatarSasha Levin <sasha.levin@oracle.com>
    References: http://lkml.kernel.org/g/53113485.2090407@oracle.comSigned-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
    b7ce40cf
file.c 21.4 KB