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    Subject[possible deadlock][3.1.0-g138c4ae] possible circular locking dependency detected
    Hi folks:

    My dmesg said that:

    ======================================================
    [ INFO: possible circular locking dependency detected ]
    3.1.0-138c4ae #2
    -------------------------------------------------------
    hugemmap05/18198 is trying to acquire lock:
    (&mm->mmap_sem){++++++}, at: [<ffffffff8114d85c>] might_fault+0x5c/0xb0

    but task is already holding lock:
    (&sb->s_type->i_mutex_key#21){+.+.+.}, at: [<ffffffff811a10f6>] vfs_readdir+0x86/0xe0

    which lock already depends on the new lock.


    the existing dependency chain (in reverse order) is:

    -> #1 (&sb->s_type->i_mutex_key#21){+.+.+.}:
    [<ffffffff810afd34>] validate_chain+0x704/0x860
    [<ffffffff810b018c>] __lock_acquire+0x2fc/0x500
    [<ffffffff810b0b01>] lock_acquire+0xb1/0x1a0
    [<ffffffff815464f2>] __mutex_lock_common+0x62/0x420
    [<ffffffff81546a1a>] mutex_lock_nested+0x4a/0x60
    [<ffffffff8120b4ba>] hugetlbfs_file_mmap+0xaa/0x160
    [<ffffffff81158071>] mmap_region+0x3e1/0x590
    [<ffffffff81158584>] do_mmap_pgoff+0x364/0x3b0
    [<ffffffff811587d9>] sys_mmap_pgoff+0x209/0x240
    [<ffffffff8101aac9>] sys_mmap+0x29/0x30
    [<ffffffff81551542>] system_call_fastpath+0x16/0x1b

    -> #0 (&mm->mmap_sem){++++++}:
    [<ffffffff810af607>] check_prev_add+0x537/0x560
    [<ffffffff810afd34>] validate_chain+0x704/0x860
    [<ffffffff810b018c>] __lock_acquire+0x2fc/0x500
    [<ffffffff810b0b01>] lock_acquire+0xb1/0x1a0
    [<ffffffff8114d889>] might_fault+0x89/0xb0
    [<ffffffff811a0f2e>] filldir+0x7e/0xe0
    [<ffffffff811b445e>] dcache_readdir+0x5e/0x230
    [<ffffffff811a1130>] vfs_readdir+0xc0/0xe0
    [<ffffffff811a12c9>] sys_getdents+0x89/0x100
    [<ffffffff81551542>] system_call_fastpath+0x16/0x1b

    other info that might help us debug this:

    Possible unsafe locking scenario:

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

    *** DEADLOCK ***

    1 lock held by hugemmap05/18198:
    #0: (&sb->s_type->i_mutex_key#21){+.+.+.}, at: [<ffffffff811a10f6>] vfs_readdir+0x86/0xe0

    stack backtrace:
    Pid: 18198, comm: hugemmap05 Not tainted 3.1.0-138c4ae #2
    Call Trace:
    [<ffffffff810ad469>] print_circular_bug+0x109/0x110
    [<ffffffff810af607>] check_prev_add+0x537/0x560
    [<ffffffff8114e112>] ? do_anonymous_page+0xf2/0x2d0
    [<ffffffff810afd34>] validate_chain+0x704/0x860
    [<ffffffff810b018c>] __lock_acquire+0x2fc/0x500
    [<ffffffff810b0b01>] lock_acquire+0xb1/0x1a0
    [<ffffffff8114d85c>] ? might_fault+0x5c/0xb0
    [<ffffffff8114d889>] might_fault+0x89/0xb0
    [<ffffffff8114d85c>] ? might_fault+0x5c/0xb0
    [<ffffffff81546763>] ? __mutex_lock_common+0x2d3/0x420
    [<ffffffff811a10f6>] ? vfs_readdir+0x86/0xe0
    [<ffffffff811a0f2e>] filldir+0x7e/0xe0
    [<ffffffff811b445e>] dcache_readdir+0x5e/0x230
    [<ffffffff811a0eb0>] ? filldir64+0xf0/0xf0
    [<ffffffff811a0eb0>] ? filldir64+0xf0/0xf0
    [<ffffffff811a0eb0>] ? filldir64+0xf0/0xf0
    [<ffffffff811a1130>] vfs_readdir+0xc0/0xe0
    [<ffffffff8118e9be>] ? fget+0xee/0x220
    [<ffffffff8118e8d0>] ? fget_raw+0x220/0x220
    [<ffffffff811a12c9>] sys_getdents+0x89/0x100
    [<ffffffff81551542>] system_call_fastpath+0x16/0x1b



    Wile hugemmap05 is a test case from LTP.
    http://ltp.git.sourceforge.net/git/gitweb.cgi?p=ltp/ltp.git;a=blob;f=testcases/kernel/mem/hugetlb/hugemmap/hugemmap05.c;h=50bb8ca23ae9686662740f9ea5d7187affff8b60;hb=HEAD

    But I don't know how to reproduce this.


    Thanks
    -Wanlong Gao


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