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

[Eric Sandeen <sandeen@redhat.com>]

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.

-Eric