Re: deadlock between &type->i_mutex_dir_key#4 and &xfs_dir_ilock_class

Dave Chinner
2015-03-30T19:40:25Z

On Mon, Mar 30, 2015 at 09:29:14AM +0200, Daniel Wagner wrote:
> Hi,
>
> Just my test box booted 4.0.0-rc6 and I was greeted by:
>
>
> [Mar30 10:10] ======================================================
> [ +0.000043] [ INFO: possible circular locking dependency detected ]
> [ +0.000045] 4.0.0-rc6 #32 Not tainted
> [ +0.000027] -------------------------------------------------------
> [ +0.000042] ls/1709 is trying to acquire lock:
> [ +0.000034] (&mm->mmap_sem){++++++}, at: [<ffffffff811e62cf>] might_fault+0x5f/0xb0
> [ +0.000083]
> but task is already holding lock:
> [ +0.000043] (&xfs_dir_ilock_class){.+.+..}, at: [<ffffffffa0424902>] xfs_ilock+0xc2/0x130 [xfs]
> [ +0.000110]
> which lock already depends on the new lock.

No deadlock. Problem is the shmem code, which is doing inode
instantiation under the mmap_sem, thereby inverting the entire vfs
locking order w.r.t. to the mmap_sem....

i.e. this one:

> -> #1 (&isec->lock){+.+.+.}:
> [ +0.000045] [<ffffffff810ef987>] lock_acquire+0xc7/0x160
> [ +0.000045] [<ffffffff817e273d>] mutex_lock_nested+0x7d/0x450
> [ +0.000045] [<ffffffff8135a755>] inode_doinit_with_dentry+0xc5/0x6a0
> [ +0.000050] [<ffffffff8135b91c>] selinux_d_instantiate+0x1c/0x20
> [ +0.001072] [<ffffffff8134ef9b>] security_d_instantiate+0x1b/0x30
> [ +0.001056] [<ffffffff81255454>] d_instantiate+0x54/0x80
> [ +0.001052] [<ffffffff811d24bc>] __shmem_file_setup+0xdc/0x250
> [ +0.001059] [<ffffffff811d5fd8>] shmem_zero_setup+0x28/0x70
> [ +0.001074] [<ffffffff811f2168>] mmap_region+0x5d8/0x5f0
> [ +0.001045] [<ffffffff811f249b>] do_mmap_pgoff+0x31b/0x400
> [ +0.001040] [<ffffffff811d6540>] vm_mmap_pgoff+0xb0/0xf0
> [ +0.001015] [<ffffffff811f07e6>] SyS_mmap_pgoff+0x116/0x2b0
> [ +0.001009] [<ffffffff8101bc12>] SyS_mmap+0x22/0x30
> [ +0.001000] [<ffffffff817e7589>] system_call_fastpath+0x12/0x17

vm_mmap_pgoff() takes the mmap_sem.

> I tried to find out if this was reported before but I
> haven't found anything. If I missed it I am sorry for the noise.

It's been reported so many times I need a FAQ entry for it. problem
is, i can't fix it easily because it's a shmem bug...

Cheers,

Dave.
--
Dave Chinner
david@fromorbit.com

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