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SubjectRe: NFS lockdep lock misordering mmap_sem<->i_mutex_key with 2.6.32-git1
Date
> 
> While booting 2.6.32-git1 on a NFS root box I got the following
> lockdep warning early at boot. I haven't looked at details.

It seems typical ABBA deadlock.

vfs_readdir [grab i_mutex]
nfs_readdir
nfs_do_filldir
filldir
copy_to_user
[page_fault] [grab mmap_sem]

sys_mmap [grab mmap_sem]
do_mmap_pgoff
mmap_region
nfs_file_mmap
nfs_revalidate_mapping
nfs_invalidate_mapping [grab i_mutex]

I guess recent lockdep improvement find old bug.



>
> -Andi
>
> VFS: Mounted root (nfs filesystem) on device 0:15.
> VFS: Mounted root (nfs filesystem) on device 0:15.
> Freeing unused kernel memory: 2376k freed
>
> =======================================================
> [ INFO: possible circular locking dependency detected ]
> -------------------------------------------------------
> udevinfo/2551 is trying to acquire lock:
> (&sb->s_type->i_mutex_key#5){+.+.+.}, at: [<ffffffff8118e0d3>] nfs_revalidate_mapping+0x7c/0xc5
>
> but task is already holding lock:
> (&mm->mmap_sem){++++++}, at: [<ffffffff8100fc83>] sys_mmap+0x76/0xc7
>
> which lock already depends on the new lock.
>
>
> the existing dependency chain (in reverse order) is:
>
> -> #1 (&mm->mmap_sem){++++++}:
> [<ffffffff81071d0b>] __lock_acquire+0x1435/0x1774
> [<ffffffff81072106>] lock_acquire+0xbc/0xd9
> [<ffffffff810baa14>] might_fault+0x84/0xa4
> [<ffffffff810ec340>] filldir+0x6a/0xcb
> [<ffffffff81189bad>] nfs_do_filldir+0x39d/0x4ac
> [<ffffffff8118a4e9>] nfs_readdir+0x82d/0x8ce
> [<ffffffff810ec4bf>] vfs_readdir+0x6c/0xa1
> [<ffffffff810ec632>] sys_getdents+0x7d/0xc9
> [<ffffffff8100ba6b>] system_call_fastpath+0x16/0x1b
>
> -> #0 (&sb->s_type->i_mutex_key#5){+.+.+.}:
> [<ffffffff81071a30>] __lock_acquire+0x115a/0x1774
> [<ffffffff81072106>] lock_acquire+0xbc/0xd9
> [<ffffffff8149210d>] mutex_lock_nested+0x68/0x2d2
> [<ffffffff8118e0d3>] nfs_revalidate_mapping+0x7c/0xc5
> [<ffffffff8118bad9>] nfs_file_mmap+0x68/0x71
> [<ffffffff810c29c0>] mmap_region+0x311/0x50f
> [<ffffffff810c2f13>] do_mmap_pgoff+0x355/0x3b8
> [<ffffffff8100fca1>] sys_mmap+0x94/0xc7
> [<ffffffff8100ba6b>] system_call_fastpath+0x16/0x1b
>
> other info that might help us debug this:
>
> 1 lock held by udevinfo/2551:
> #0: (&mm->mmap_sem){++++++}, at: [<ffffffff8100fc83>] sys_mmap+0x76/0xc7
>
> stack backtrace:
> Pid: 2551, comm: udevinfo Not tainted 2.6.32-git1 #31
> Call Trace:
> [<ffffffff81070388>] print_circular_bug+0xb3/0xc2
> [<ffffffff81071a30>] __lock_acquire+0x115a/0x1774
> [<ffffffff810a401d>] ? find_get_pages_tag+0x0/0x12a
> [<ffffffff81072106>] lock_acquire+0xbc/0xd9
> [<ffffffff8118e0d3>] ? nfs_revalidate_mapping+0x7c/0xc5
> [<ffffffff8149210d>] mutex_lock_nested+0x68/0x2d2
> [<ffffffff8118e0d3>] ? nfs_revalidate_mapping+0x7c/0xc5
> [<ffffffff8118e0d3>] ? nfs_revalidate_mapping+0x7c/0xc5
> [<ffffffff810c291d>] ? mmap_region+0x26e/0x50f
> [<ffffffff8118e0d3>] nfs_revalidate_mapping+0x7c/0xc5
> [<ffffffff8118bad9>] nfs_file_mmap+0x68/0x71
> [<ffffffff810c29c0>] mmap_region+0x311/0x50f
> [<ffffffff810c2f13>] do_mmap_pgoff+0x355/0x3b8
> [<ffffffff8100fca1>] sys_mmap+0x94/0xc7
> [<ffffffff8100ba6b>] system_call_fastpath+0x16/0x1b
>
> -Andi
> --
> ak@linux.intel.com -- Speaking for myself only.
> --
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