hugetlbfs lockdep spew revisited.

[Dave Jones]

Remember this ? https://lkml.org/lkml/2011/4/15/272
Josh took a stab at fixing it in e096d0c7e2e4e5893792db865dd065ac73cf1f00,
but it seems to still be there.

	Dave


======================================================
[ INFO: possible circular locking dependency detected ]
3.3.0-rc3+ #2 Not tainted
-------------------------------------------------------
trinity/30663 is trying to acquire lock:
 (&sb->s_type->i_mutex_key#18){+.+...}, at: [<ffffffff81298169>] hugetlbfs_file_mmap+0x89/0x140

but task is already holding lock:
 (&mm->mmap_sem){++++++}, at: [<ffffffff81182d97>] sys_mmap_pgoff+0x1d7/0x230

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (&mm->mmap_sem){++++++}:
       [<ffffffff810d073d>] lock_acquire+0x9d/0x220
       [<ffffffff811789c0>] might_fault+0x80/0xb0
       [<ffffffff811d2997>] filldir+0x77/0xe0
       [<ffffffff811e61ae>] dcache_readdir+0x5e/0x220
       [<ffffffff811d2c68>] vfs_readdir+0xb8/0xf0
       [<ffffffff811d2d99>] sys_getdents+0x89/0x100
       [<ffffffff816a5b69>] system_call_fastpath+0x16/0x1b

-> #0 (&sb->s_type->i_mutex_key#18){+.+...}:
       [<ffffffff810d0008>] __lock_acquire+0x1bf8/0x1c20
       [<ffffffff810d073d>] lock_acquire+0x9d/0x220
       [<ffffffff8169a5b9>] __mutex_lock_common+0x59/0x500
       [<ffffffff8169ab94>] mutex_lock_nested+0x44/0x50
       [<ffffffff81298169>] hugetlbfs_file_mmap+0x89/0x140
       [<ffffffff811826a9>] mmap_region+0x369/0x4f0
       [<ffffffff81182b9f>] do_mmap_pgoff+0x36f/0x390
       [<ffffffff81182db7>] sys_mmap_pgoff+0x1f7/0x230
       [<ffffffff8101eda2>] sys_mmap+0x22/0x30
       [<ffffffff816a5b69>] system_call_fastpath+0x16/0x1b

other info that might help us debug this:

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&mm->mmap_sem);
                               lock(&sb->s_type->i_mutex_key#18);
                               lock(&mm->mmap_sem);
  lock(&sb->s_type->i_mutex_key#18);

 *** DEADLOCK ***

1 lock held by trinity/30663:
 #0:  (&mm->mmap_sem){++++++}, at: [<ffffffff81182d97>] sys_mmap_pgoff+0x1d7/0x230

stack backtrace:
Pid: 30663, comm: trinity Not tainted 3.3.0-rc3+ #2
Call Trace:
 [<ffffffff816924d7>] print_circular_bug+0x1fb/0x20c
 [<ffffffff810d0008>] __lock_acquire+0x1bf8/0x1c20
 [<ffffffff816a1c2d>] ? sub_preempt_count+0x9d/0xd0
 [<ffffffff811a40cc>] ? deactivate_slab+0x54c/0x5f0
 [<ffffffff810d073d>] lock_acquire+0x9d/0x220
 [<ffffffff81298169>] ? hugetlbfs_file_mmap+0x89/0x140
 [<ffffffff810d12fd>] ? trace_hardirqs_on_caller+0x10d/0x1a0
 [<ffffffff8169a5b9>] __mutex_lock_common+0x59/0x500
 [<ffffffff81298169>] ? hugetlbfs_file_mmap+0x89/0x140
 [<ffffffff811825e5>] ? mmap_region+0x2a5/0x4f0
 [<ffffffff81298169>] ? hugetlbfs_file_mmap+0x89/0x140
 [<ffffffff8169ab94>] mutex_lock_nested+0x44/0x50
 [<ffffffff81298169>] hugetlbfs_file_mmap+0x89/0x140
 [<ffffffff811826a9>] mmap_region+0x369/0x4f0
 [<ffffffff812c1e9a>] ? file_map_prot_check+0xaa/0xe0
 [<ffffffff81182b9f>] do_mmap_pgoff+0x36f/0x390
 [<ffffffff81182d97>] ? sys_mmap_pgoff+0x1d7/0x230
 [<ffffffff81182db7>] sys_mmap_pgoff+0x1f7/0x230
 [<ffffffff810d12fd>] ? trace_hardirqs_on_caller+0x10d/0x1a0
 [<ffffffff8101eda2>] sys_mmap+0x22/0x30
 [<ffffffff816a5b69>] system_call_fastpath+0x16/0x1b

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