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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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