lockdep wierdness...

[Trond Myklebust]

I'm seeing lockdep warning about a potential lock inversion between
&mm->mmap_sem and &inode->i_mutex in NFS (see attachment).

Unfortunately the basis for the warning appears to be the behaviour in
ext3(???). AFAICS there is no way for NFS to share an inode->i_mutex
with ext3. What to do?

Trond
=======================================================
[ INFO: possible circular locking dependency detected ]
2.6.23-rc7-g8809e921 #1
-------------------------------------------------------
beagle-build-in/24375 is trying to acquire lock:
 (&mm->mmap_sem){----}, at: [<c05a2887>] do_page_fault+0x17d/0x591

but task is already holding lock:
 (&inode->i_mutex){--..}, at: [<c059f9e3>] mutex_lock+0x1c/0x1f

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (&inode->i_mutex){--..}:
       [<c043d4da>] __lock_acquire+0x9f3/0xba6
       [<c043da62>] lock_acquire+0x5f/0x78
       [<c059f832>] __mutex_lock_slowpath+0xe5/0x27a
       [<c059f9e3>] mutex_lock+0x1c/0x1f
       [<f8c92495>] nfs_revalidate_mapping+0x64/0x9c [nfs]
       [<f8c8ff2a>] nfs_file_mmap+0x46/0x75 [nfs]
       [<c046097c>] mmap_region+0x1ea/0x3b8
       [<c0460e9b>] do_mmap_pgoff+0x27b/0x2da
       [<c0407d77>] sys_mmap2+0x9b/0xb5
       [<c040405e>] sysenter_past_esp+0x5f/0x99
       [<ffffffff>] 0xffffffff

-> #0 (&mm->mmap_sem){----}:
       [<c043d3c6>] __lock_acquire+0x8df/0xba6
       [<c043da62>] lock_acquire+0x5f/0x78
       [<c04360db>] down_read+0x3a/0x4c
       [<c05a2887>] do_page_fault+0x17d/0x591
       [<c05a1382>] error_code+0x72/0x78
       [<f88acaac>] call_filldir+0xac/0xc3 [ext3]
       [<f88acdb2>] ext3_readdir+0x217/0x5e5 [ext3]
       [<c04798a1>] vfs_readdir+0x67/0x93
       [<c0479af6>] sys_getdents+0x5f/0x9d
       [<c040405e>] sysenter_past_esp+0x5f/0x99
       [<ffffffff>] 0xffffffff

other info that might help us debug this:

1 lock held by beagle-build-in/24375:
 #0:  (&inode->i_mutex){--..}, at: [<c059f9e3>] mutex_lock+0x1c/0x1f

stack backtrace:
 [<c04050ee>] show_trace_log_lvl+0x1a/0x2f
 [<c0405b58>] show_trace+0x12/0x14
 [<c0405b70>] dump_stack+0x16/0x18
 [<c043bc05>] print_circular_bug_tail+0x5f/0x68
 [<c043d3c6>] __lock_acquire+0x8df/0xba6
 [<c043da62>] lock_acquire+0x5f/0x78
 [<c04360db>] down_read+0x3a/0x4c
 [<c05a2887>] do_page_fault+0x17d/0x591
 [<c05a1382>] error_code+0x72/0x78
 [<f88acaac>] call_filldir+0xac/0xc3 [ext3]
 [<f88acdb2>] ext3_readdir+0x217/0x5e5 [ext3]
 [<c04798a1>] vfs_readdir+0x67/0x93
 [<c0479af6>] sys_getdents+0x5f/0x9d
 [<c040405e>] sysenter_past_esp+0x5f/0x99
 =======================