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    Subject[PATCH] hugetlbfs: lockdep annotate root inode properly
    Date
    From: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>

    This fix the below lockdep warning

    ======================================================
    [ INFO: possible circular locking dependency detected ]
    3.3.0-rc4+ #190 Not tainted
    -------------------------------------------------------
    shared/1568 is trying to acquire lock:
    (&sb->s_type->i_mutex_key#12){+.+.+.}, at: [<ffffffff811efa0f>] hugetlbfs_file_mmap+0x7d/0x108

    but task is already holding lock:
    (&mm->mmap_sem){++++++}, at: [<ffffffff810f5589>] sys_mmap_pgoff+0xd4/0x12f

    which lock already depends on the new lock.


    the existing dependency chain (in reverse order) is:

    -> #1 (&mm->mmap_sem){++++++}:
    [<ffffffff8109fb8f>] lock_acquire+0xd5/0xfa
    [<ffffffff810ee439>] might_fault+0x6d/0x90
    [<ffffffff8111bc12>] filldir+0x6a/0xc2
    [<ffffffff81129942>] dcache_readdir+0x5c/0x222
    [<ffffffff8111be58>] vfs_readdir+0x76/0xac
    [<ffffffff8111bf6a>] sys_getdents+0x79/0xc9
    [<ffffffff816940a2>] system_call_fastpath+0x16/0x1b

    -> #0 (&sb->s_type->i_mutex_key#12){+.+.+.}:
    [<ffffffff8109f40a>] __lock_acquire+0xa6c/0xd60
    [<ffffffff8109fb8f>] lock_acquire+0xd5/0xfa
    [<ffffffff816916be>] __mutex_lock_common+0x48/0x350
    [<ffffffff81691a85>] mutex_lock_nested+0x2a/0x31
    [<ffffffff811efa0f>] hugetlbfs_file_mmap+0x7d/0x108
    [<ffffffff810f4fd0>] mmap_region+0x26f/0x466
    [<ffffffff810f545b>] do_mmap_pgoff+0x294/0x2ee
    [<ffffffff810f55a9>] sys_mmap_pgoff+0xf4/0x12f
    [<ffffffff8103d1f2>] sys_mmap+0x1d/0x1f
    [<ffffffff816940a2>] 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#12);
    lock(&mm->mmap_sem);
    lock(&sb->s_type->i_mutex_key#12);

    *** DEADLOCK ***

    1 lock held by shared/1568:
    #0: (&mm->mmap_sem){++++++}, at: [<ffffffff810f5589>] sys_mmap_pgoff+0xd4/0x12f

    stack backtrace:
    Pid: 1568, comm: shared Not tainted 3.3.0-rc4+ #190
    Call Trace:
    [<ffffffff81688bf9>] print_circular_bug+0x1f8/0x209
    [<ffffffff8109f40a>] __lock_acquire+0xa6c/0xd60
    [<ffffffff8110e7b6>] ? files_lglock_local_lock_cpu+0x61/0x61
    [<ffffffff811efa0f>] ? hugetlbfs_file_mmap+0x7d/0x108
    [<ffffffff8109fb8f>] lock_acquire+0xd5/0xfa
    [<ffffffff811efa0f>] ? hugetlbfs_file_mmap+0x7d/0x108

    Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
    ---
    fs/hugetlbfs/inode.c | 1 +
    1 files changed, 1 insertions(+), 0 deletions(-)

    NOTE: This patch also require
    http://thread.gmane.org/gmane.linux.file-systems/58795/focus=59565
    to remove the lockdep warning

    diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
    index 3645cd3..ca4fa70 100644
    --- a/fs/hugetlbfs/inode.c
    +++ b/fs/hugetlbfs/inode.c
    @@ -459,6 +459,7 @@ static struct inode *hugetlbfs_get_root(struct super_block *sb,
    inode->i_fop = &simple_dir_operations;
    /* directory inodes start off with i_nlink == 2 (for "." entry) */
    inc_nlink(inode);
    + lockdep_annotate_inode_mutex_key(inode);
    }
    return inode;
    }
    --
    1.7.9


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