[PATCH] Btrfs: avoid deadlock in btrfs_async_run_delayed_root

[PATCH] Btrfs: avoid deadlock in btrfs_async_run_delayed_root

[Liu Bo]

Here %path is set with ->leave_spinning=1, thus it'll hold the rwlock
after btrfs_search_slot(), however, when processing delayed items in
__btrfs_commit_inode_delayed_items(), it goes to acquire node->mutex
which might sleep, that is, it may sleep under spin_lock.

Given node->mutex is necessary to avoid race between async works, this
remove the ->leave_spining setting.

Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
---
 fs/btrfs/delayed-inode.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/fs/btrfs/delayed-inode.c b/fs/btrfs/delayed-inode.c
index 19e4ad2..a857a2f 100644
--- a/fs/btrfs/delayed-inode.c
+++ b/fs/btrfs/delayed-inode.c
@@ -1331,7 +1331,6 @@ static void btrfs_async_run_delayed_root(struct btrfs_work *work)
 	if (!delayed_node)
 		goto free_path;
 
-	path->leave_spinning = 1;
 	root = delayed_node->root;
 
 	trans = btrfs_join_transaction(root);
-- 
2.9.4

Re: [PATCH] Btrfs: avoid deadlock in btrfs_async_run_delayed_root

[Liu Bo]

Hi,

Please ignore this patch, I misunderstood the lock order.

thanks,

-liubo

On Fri, Oct 20, 2017 at 05:40:12PM -0600, Liu Bo wrote:
> Here %path is set with ->leave_spinning=1, thus it'll hold the rwlock
> after btrfs_search_slot(), however, when processing delayed items in
> __btrfs_commit_inode_delayed_items(), it goes to acquire node->mutex
> which might sleep, that is, it may sleep under spin_lock.
> 
> Given node->mutex is necessary to avoid race between async works, this
> remove the ->leave_spining setting.
> 
> Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
> ---
>  fs/btrfs/delayed-inode.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/fs/btrfs/delayed-inode.c b/fs/btrfs/delayed-inode.c
> index 19e4ad2..a857a2f 100644
> --- a/fs/btrfs/delayed-inode.c
> +++ b/fs/btrfs/delayed-inode.c
> @@ -1331,7 +1331,6 @@ static void btrfs_async_run_delayed_root(struct btrfs_work *work)
>  	if (!delayed_node)
>  		goto free_path;
>  
> -	path->leave_spinning = 1;
>  	root = delayed_node->root;
>  
>  	trans = btrfs_join_transaction(root);
> -- 
> 2.9.4
> 
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