This is one of two patches which are to correct possible circular
locking between mm->mmap_sem and nilfs->ns_segctor_sem.
The problem was detected by lockdep check as follows:
=======================================================
[ INFO: possible circular locking dependency detected ]
2.6.30-rc3-nilfs-00002-g3552613 #6
-------------------------------------------------------
mmap/5418 is trying to acquire lock:
(&nilfs->ns_segctor_sem){++++.+}, at: [<d0d0e852>] nilfs_transaction_begin+0xb6/0x10c [nilfs2]
but task is already holding lock:
(&mm->mmap_sem){++++++}, at: [<c043700a>] do_page_fault+0x1d8/0x30a
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #1 (&mm->mmap_sem){++++++}:
[<c01470a5>] __lock_acquire+0x1066/0x13b0
[<c01474a9>] lock_acquire+0xba/0xdd
[<c01836bc>] might_fault+0x68/0x88
[<c023c730>] copy_to_user+0x2c/0xfc
[<d0d11b4f>] nilfs_ioctl_wrap_copy+0x103/0x160 [nilfs2]
[<d0d11fa9>] nilfs_ioctl+0x30a/0x3b0 [nilfs2]
[<c01a3be7>] vfs_ioctl+0x22/0x69
[<c01a408e>] do_vfs_ioctl+0x460/0x499
[<c01a4107>] sys_ioctl+0x40/0x5a
[<c01031a4>] sysenter_do_call+0x12/0x38
[<ffffffff>] 0xffffffff
-> #0 (&nilfs->ns_segctor_sem){++++.+}:
[<c0146e0b>] __lock_acquire+0xdcc/0x13b0
[<c01474a9>] lock_acquire+0xba/0xdd
[<c0433f1d>] down_read+0x2a/0x3e
[<d0d0e852>] nilfs_transaction_begin+0xb6/0x10c [nilfs2]
[<d0cfe0e5>] nilfs_page_mkwrite+0xe7/0x154 [nilfs2]
[<c0183b0b>] __do_fault+0x165/0x376
[<c01855cd>] handle_mm_fault+0x287/0x5d1
[<c043712d>] do_page_fault+0x2fb/0x30a
[<c0435462>] error_code+0x72/0x78
[<ffffffff>] 0xffffffff
other info that might help us debug this:
1 lock held by mmap/5418:
#0: (&mm->mmap_sem){++++++}, at: [<c043700a>] do_page_fault+0x1d8/0x30a
stack backtrace:
Pid: 5418, comm: mmap Not tainted 2.6.30-rc3-nilfs-00002-g3552613 #6
Call Trace:
[<c0432145>] ? printk+0xf/0x12
[<c0145c48>] print_circular_bug_tail+0xaa/0xb5
[<c0146e0b>] __lock_acquire+0xdcc/0x13b0
[<d0d10149>] ? nilfs_sufile_get_stat+0x1e/0x105 [nilfs2]
[<c013b59a>] ? up_read+0x16/0x2c
[<d0d10225>] ? nilfs_sufile_get_stat+0xfa/0x105 [nilfs2]
[<c01474a9>] lock_acquire+0xba/0xdd
[<d0d0e852>] ? nilfs_transaction_begin+0xb6/0x10c [nilfs2]
[<c0433f1d>] down_read+0x2a/0x3e
[<d0d0e852>] ? nilfs_transaction_begin+0xb6/0x10c [nilfs2]
[<d0d0e852>] nilfs_transaction_begin+0xb6/0x10c [nilfs2]
[<d0cfe0e5>] nilfs_page_mkwrite+0xe7/0x154 [nilfs2]
[<c0183b0b>] __do_fault+0x165/0x376
[<c01855cd>] handle_mm_fault+0x287/0x5d1
[<c043700a>] ? do_page_fault+0x1d8/0x30a
[<c013b54f>] ? down_read_trylock+0x39/0x43
[<c043712d>] do_page_fault+0x2fb/0x30a
[<c0436e32>] ? do_page_fault+0x0/0x30a
[<c0435462>] error_code+0x72/0x78
[<c0436e32>] ? do_page_fault+0x0/0x30a
This makes the lock granularity of nilfs->ns_segctor_sem finer than
that of the mmap semaphore for ioctl commands except
nilfs_clean_segments().
The successive patch ("nilfs2: fix lock order reversal in
nilfs_clean_segments ioctl") is required to fully resolve the problem.
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
47eb6b9c8f