Re: I think "btrfs: fix leak of path in btrfs_find_item" broke stable trees ...

[Chris Mason <clm@fb.com>]

On Thu, Mar 26, 2015 at 10:11 AM, Eric Sandeen <sandeen@redhat.com> 
wrote:
> On 3/26/15 5:23 AM, Filipe David Manana wrote:
>>  On Thu, Mar 26, 2015 at 3:24 AM, Eric Sandeen <sandeen@redhat.com> 
>> wrote:
>>>  Looks like "btrfs: fix leak of path in btrfs_find_item" got sent
>>>  to stable trees, but in my testing, it causes deadlocks on mount:
>>> 
>>>  [23379.359246] mount           D 0000000000000000     0 22541  
>>> 22274 0x00000080
>>>  [23379.366326]  ffff8803ebadf6c8 0000000000000086 ffff88027ff10230 
>>> 0000000000013680
>>>  [23379.373770]  0000000000013680 ffff8803ebadffd8 ffff8803ebadc010 
>>> 0000000000013680
>>>  [23379.381208]  ffff8803ebadffd8 0000000000013680 ffff880261c78b60 
>>> ffff8802140a0b60
>>>  [23379.388648] Call Trace:
>>>  [23379.391106]  [<ffffffff816182b9>] schedule+0x29/0x70
>>>  [23379.396091]  [<ffffffffa06b82f5>] btrfs_tree_lock+0xb5/0x290 
>>> [btrfs]
>>>  [23379.402444]  [<ffffffff8109b470>] ? wake_up_bit+0x40/0x40
>>>  [23379.407855]  [<ffffffffa064f7a5>] ? 
>>> generic_bin_search+0xf5/0x180 [btrfs]
>>>  [23379.414643]  [<ffffffffa065041b>] 
>>> btrfs_lock_root_node+0x3b/0x50 [btrfs]
>>>  [23379.421345]  [<ffffffffa065936b>] btrfs_search_slot+0x63b/0x800 
>>> [btrfs]
>>>  [23379.427956]  [<ffffffffa064fa49>] ? 
>>> btrfs_set_path_blocking+0x39/0x80 [btrfs]
>>>  [23379.435088]  [<ffffffffa0659ede>] 
>>> btrfs_insert_empty_items+0x7e/0xe0 [btrfs]
>>>  [23379.442125]  [<ffffffffa065051a>] ? btrfs_alloc_path+0x1a/0x20 
>>> [btrfs]
>>>  [23379.448655]  [<ffffffffa06b8989>] 
>>> btrfs_insert_orphan_item+0x69/0x90 [btrfs]
>>>  [23379.455696]  [<ffffffffa06ba938>] insert_orphan_item+0x68/0x90 
>>> [btrfs]
>>>  [23379.462251]  [<ffffffffa06bf772>] replay_one_buffer+0x372/0x380 
>>> [btrfs]
>>>  [23379.468878]  [<ffffffffa069a4c1>] ? 
>>> mark_extent_buffer_accessed+0x51/0x70 [btrfs]
>>>  [23379.476372]  [<ffffffffa06ba54b>] walk_up_log_tree+0x1cb/0x250 
>>> [btrfs]
>>>  [23379.482910]  [<ffffffffa06ba68f>] walk_log_tree+0xbf/0x1b0 
>>> [btrfs]
>>>  [23379.489098]  [<ffffffffa06bd51c>] 
>>> btrfs_recover_log_trees+0x1ec/0x4c0 [btrfs]
>>>  ...
>>> 
>>>  I could hit this by running ./check generic/015  generic/039 in 
>>> fstests,
>>>  with a SCRATCH_DEV_POOL defined (not sure it matters, it's just 
>>> what I
>>>  have...)
>>> 
>>>  This fixes it, though I'm not totally sure why.  Refcounts?
>> 
>>  Hi Eric,
>> 
>>  Your patch seems correct to me.
>>  The problem is that btrfs_insert_orphan_item tries to get a write 
>> lock
>>  on the same node/leaf for which its caller (insert_orphan_item) is
>>  already holding a read lock.
>> 
>>  If you plan to submit a proper patch, feel free to add my 
>> Reviewed-by:
>>  Filipe Manana <fdmanana@suse.com>
> 
> Thanks; well -
> 
>>>  but it never likely showed up upstream, because
>>> 
>>>  9c4f61f btrfs: simplify insert_orphan_item
>>> 
>>>  made the whole path alloc/free go away.
> 
> so I think there's no need for my patch; may as well just send the 
> above to stable
> and fix it that way, as long as 9c4f61f is deemed safe & correct, I 
> think.

Nice catch, thanks Eric.  9c4f61f looks fine for stable to me, but 
since he's already testing on stable, I talked Eric into giving it a 
pass through xfstests before I send it up.

-chris