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    Subject[90/90] ext4: Fix potential fiemap deadlock (mmap_sem vs. i_data_sem)
    2.6.31-stable review patch.  If anyone has any objections, please let us know.

    ------------------
    (cherry picked from commit fab3a549e204172236779f502eccb4f9bf0dc87d)

    Fix the following potential circular locking dependency between
    mm->mmap_sem and ei->i_data_sem:

    =======================================================
    [ INFO: possible circular locking dependency detected ]
    2.6.32-04115-gec044c5 #37
    -------------------------------------------------------
    ureadahead/1855 is trying to acquire lock:
    (&mm->mmap_sem){++++++}, at: [<ffffffff81107224>] might_fault+0x5c/0xac

    but task is already holding lock:
    (&ei->i_data_sem){++++..}, at: [<ffffffff811be1fd>] ext4_fiemap+0x11b/0x159

    which lock already depends on the new lock.

    the existing dependency chain (in reverse order) is:

    -> #1 (&ei->i_data_sem){++++..}:
    [<ffffffff81099bfa>] __lock_acquire+0xb67/0xd0f
    [<ffffffff81099e7e>] lock_acquire+0xdc/0x102
    [<ffffffff81516633>] down_read+0x51/0x84
    [<ffffffff811a2414>] ext4_get_blocks+0x50/0x2a5
    [<ffffffff811a3453>] ext4_get_block+0xab/0xef
    [<ffffffff81154f39>] do_mpage_readpage+0x198/0x48d
    [<ffffffff81155360>] mpage_readpages+0xd0/0x114
    [<ffffffff811a104b>] ext4_readpages+0x1d/0x1f
    [<ffffffff810f8644>] __do_page_cache_readahead+0x12f/0x1bc
    [<ffffffff810f86f2>] ra_submit+0x21/0x25
    [<ffffffff810f0cfd>] filemap_fault+0x19f/0x32c
    [<ffffffff81107b97>] __do_fault+0x55/0x3a2
    [<ffffffff81109db0>] handle_mm_fault+0x327/0x734
    [<ffffffff8151aaa9>] do_page_fault+0x292/0x2aa
    [<ffffffff81518205>] page_fault+0x25/0x30
    [<ffffffff812a34d8>] clear_user+0x38/0x3c
    [<ffffffff81167e16>] padzero+0x20/0x31
    [<ffffffff81168b47>] load_elf_binary+0x8bc/0x17ed
    [<ffffffff81130e95>] search_binary_handler+0xc2/0x259
    [<ffffffff81166d64>] load_script+0x1b8/0x1cc
    [<ffffffff81130e95>] search_binary_handler+0xc2/0x259
    [<ffffffff8113255f>] do_execve+0x1ce/0x2cf
    [<ffffffff81027494>] sys_execve+0x43/0x5a
    [<ffffffff8102918a>] stub_execve+0x6a/0xc0

    -> #0 (&mm->mmap_sem){++++++}:
    [<ffffffff81099aa4>] __lock_acquire+0xa11/0xd0f
    [<ffffffff81099e7e>] lock_acquire+0xdc/0x102
    [<ffffffff81107251>] might_fault+0x89/0xac
    [<ffffffff81139382>] fiemap_fill_next_extent+0x95/0xda
    [<ffffffff811bcb43>] ext4_ext_fiemap_cb+0x138/0x157
    [<ffffffff811be069>] ext4_ext_walk_space+0x178/0x1f1
    [<ffffffff811be21e>] ext4_fiemap+0x13c/0x159
    [<ffffffff811390e6>] do_vfs_ioctl+0x348/0x4d6
    [<ffffffff811392ca>] sys_ioctl+0x56/0x79
    [<ffffffff81028cb2>] system_call_fastpath+0x16/0x1b

    other info that might help us debug this:

    1 lock held by ureadahead/1855:
    #0: (&ei->i_data_sem){++++..}, at: [<ffffffff811be1fd>] ext4_fiemap+0x11b/0x159

    stack backtrace:
    Pid: 1855, comm: ureadahead Not tainted 2.6.32-04115-gec044c5 #37
    Call Trace:
    [<ffffffff81098c70>] print_circular_bug+0xa8/0xb7
    [<ffffffff81099aa4>] __lock_acquire+0xa11/0xd0f
    [<ffffffff8102f229>] ? sched_clock+0x9/0xd
    [<ffffffff81099e7e>] lock_acquire+0xdc/0x102
    [<ffffffff81107224>] ? might_fault+0x5c/0xac
    [<ffffffff81107251>] might_fault+0x89/0xac
    [<ffffffff81107224>] ? might_fault+0x5c/0xac
    [<ffffffff81124b44>] ? __kmalloc+0x13b/0x18c
    [<ffffffff81139382>] fiemap_fill_next_extent+0x95/0xda
    [<ffffffff811bcb43>] ext4_ext_fiemap_cb+0x138/0x157
    [<ffffffff811bca0b>] ? ext4_ext_fiemap_cb+0x0/0x157
    [<ffffffff811be069>] ext4_ext_walk_space+0x178/0x1f1
    [<ffffffff811be21e>] ext4_fiemap+0x13c/0x159
    [<ffffffff81107224>] ? might_fault+0x5c/0xac
    [<ffffffff811390e6>] do_vfs_ioctl+0x348/0x4d6
    [<ffffffff8129f6d0>] ? __up_read+0x8d/0x95
    [<ffffffff81517fb5>] ? retint_swapgs+0x13/0x1b
    [<ffffffff811392ca>] sys_ioctl+0x56/0x79
    [<ffffffff81028cb2>] system_call_fastpath+0x16/0x1b

    Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
    Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
    ---
    fs/ext4/extents.c | 4 ++--
    1 file changed, 2 insertions(+), 2 deletions(-)

    --- a/fs/ext4/extents.c
    +++ b/fs/ext4/extents.c
    @@ -1742,7 +1742,9 @@ int ext4_ext_walk_space(struct inode *in
    while (block < last && block != EXT_MAX_BLOCK) {
    num = last - block;
    /* find extent for this block */
    + down_read(&EXT4_I(inode)->i_data_sem);
    path = ext4_ext_find_extent(inode, block, path);
    + up_read(&EXT4_I(inode)->i_data_sem);
    if (IS_ERR(path)) {
    err = PTR_ERR(path);
    path = NULL;
    @@ -3707,10 +3709,8 @@ int ext4_fiemap(struct inode *inode, str
    * Walk the extent tree gathering extent information.
    * ext4_ext_fiemap_cb will push extents back to user.
    */
    - down_read(&EXT4_I(inode)->i_data_sem);
    error = ext4_ext_walk_space(inode, start_blk, len_blks,
    ext4_ext_fiemap_cb, fieinfo);
    - up_read(&EXT4_I(inode)->i_data_sem);
    }

    return error;



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