On Sat, Dec 14, 2013 at 2:56 PM, Shilong Wang <wangshilong1991@xxxxxxxxx> wrote:
> Hello Filipe,
>
> 2013/12/14 Filipe David Borba Manana <fdmanana@xxxxxxxxx>:
>> Wang Shilong got into a case where during inode eviction we were
>> removing an extent map while it was pinned. This triggered a warning
>> in remove_extent_mapping() because the extent map had the pinned
>> flag set:
>>
>> [ 1209.102076] [<ffffffffa04721b9>] remove_extent_mapping+0x69/0x70 [btrfs]
>> [ 1209.102084] [<ffffffffa0466b06>] btrfs_evict_inode+0x96/0x4d0 [btrfs]
>> [ 1209.102089] [<ffffffff81073010>] ? wake_atomic_t_function+0x40/0x40
>> [ 1209.102092] [<ffffffff8118ab2e>] evict+0x9e/0x190
>> [ 1209.102094] [<ffffffff8118b313>] iput+0xf3/0x180
>> [ 1209.102101] [<ffffffffa0461fd1>] btrfs_run_delayed_iputs+0xb1/0xd0 [btrfs]
>> [ 1209.102107] [<ffffffffa045d358>] __btrfs_end_transaction+0x268/0x350 [btrfs]
>>
>> Therefore wait for any pending ordered extents, if any, which will
>> trigger calls to unpin_extent_cache(), before removing the extent maps.
>>
>> Wang's solution of simply clearing the pinned bit wasn't enough, as after
>> unpin_extent_cache() will be called and trigger another WARN_ON() because
>> the lookup for the extent map returned NULL.
>
> Why not in evict_inode_truncate_pages() move remove_extent_mapping() after
> clear_extent_bit()?
So, if the pinned bit is set, it means some task will clear it later,
via unpin_extent_cache(). And if you look at that function, it has
this:
write_lock(&tree->lock);
em = lookup_extent_mapping(tree, start, len);
WARN_ON(!em || em->start != start);
And remove_extent_mapping() will remove the em from the rbtree,
regardless of its reference count value, therefore triggering that
warning above.
Does it makes sense?
thanks
>
> Thanks,
> Wang
>>
>> Thanks Wang for finding out this.
>>
>> Signed-off-by: Filipe David Borba Manana <fdmanana@xxxxxxxxx>
>> ---
>> fs/btrfs/inode.c | 5 +++--
>> 1 file changed, 3 insertions(+), 2 deletions(-)
>>
>> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
>> index e889779..c2933fb 100644
>> --- a/fs/btrfs/inode.c
>> +++ b/fs/btrfs/inode.c
>> @@ -4509,6 +4509,9 @@ static void evict_inode_truncate_pages(struct inode *inode)
>> ASSERT(inode->i_state & I_FREEING);
>> truncate_inode_pages(&inode->i_data, 0);
>>
>> + /* do we really want it for ->i_nlink > 0 and zero btrfs_root_refs? */
>> + btrfs_wait_ordered_range(inode, 0, (u64)-1);
>> +
>> write_lock(&map_tree->lock);
>> while (!RB_EMPTY_ROOT(&map_tree->map)) {
>> struct extent_map *em;
>> @@ -4566,8 +4569,6 @@ void btrfs_evict_inode(struct inode *inode)
>> btrfs_orphan_del(NULL, inode);
>> goto no_delete;
>> }
>> - /* do we really want it for ->i_nlink > 0 and zero btrfs_root_refs? */
>> - btrfs_wait_ordered_range(inode, 0, (u64)-1);
>>
>> if (root->fs_info->log_root_recovering) {
>> BUG_ON(test_bit(BTRFS_INODE_HAS_ORPHAN_ITEM,
>> --
>> 1.7.9.5
>>
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
>> the body of a message to majordomo@xxxxxxxxxxxxxxx
>> More majordomo info at http://vger.kernel.org/majordomo-info.html
--
Filipe David Manana,
"Reasonable men adapt themselves to the world.
Unreasonable men adapt the world to themselves.
That's why all progress depends on unreasonable men."
--
To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
