Re: [PATCH] btrfs: fix error handling when run_delayed_extent_op fails

[Jeff Mahoney]

On 12/20/16 1:00 PM, David Sterba wrote:
> On Tue, Dec 13, 2016 at 02:33:33PM -0500, Jeff Mahoney wrote:
>> In __btrfs_run_delayed_refs, the error path when run_delayed_extent_op
>> fails sets locked_ref->processing = 0 but doesn't re-increment
>> delayed_refs->num_heads_ready.  As a result, we can end up triggering
>> the WARN_ON in btrfs_select_ref_head since the head remains in the tree
>> with ->processing = 0 and the ready count is off.
>>
>> Fixes: d7df2c796d7 (Btrfs: attach delayed ref updates to delayed ref heads)
>> Reported-by: Jon Nelson 
>> Signed-off-by: Jeff Mahoney 
>> ---
>>  fs/btrfs/extent-tree.c | 1 +
>>  1 file changed, 1 insertion(+)
>>
>> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
>> index 4607af3..73a8d31 100644
>> --- a/fs/btrfs/extent-tree.c
>> +++ b/fs/btrfs/extent-tree.c
>> @@ -2588,6 +2588,7 @@ static noinline int __btrfs_run_delayed_refs(struct 
>> btrfs_trans_handle *trans,
>>  if (must_insert_reserved)
>>  
>> locked_ref->must_insert_reserved = 1;
>>  locked_ref->processing = 0;
>> +delayed_refs->num_heads_ready++;
> 
> I think this requires spin lock/unlock around the increment, as do other
> similar places that fixup num_heads_ready after previous error.
> 

Thanks, I'll fix that.  It looks like the locking for the next block up
is also broken -- we unlock the locked_ref and then set ->processing =
0.  I'll send a patch for that as well.

-Jeff

-- 
Jeff Mahoney
SUSE Labs



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Re: [PATCH] btrfs: fix error handling when run_delayed_extent_op fails

[David Sterba]

On Tue, Dec 13, 2016 at 02:33:33PM -0500, Jeff Mahoney wrote:
> In __btrfs_run_delayed_refs, the error path when run_delayed_extent_op
> fails sets locked_ref->processing = 0 but doesn't re-increment
> delayed_refs->num_heads_ready.  As a result, we can end up triggering
> the WARN_ON in btrfs_select_ref_head since the head remains in the tree
> with ->processing = 0 and the ready count is off.
> 
> Fixes: d7df2c796d7 (Btrfs: attach delayed ref updates to delayed ref heads)
> Reported-by: Jon Nelson 
> Signed-off-by: Jeff Mahoney 
> ---
>  fs/btrfs/extent-tree.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
> index 4607af3..73a8d31 100644
> --- a/fs/btrfs/extent-tree.c
> +++ b/fs/btrfs/extent-tree.c
> @@ -2588,6 +2588,7 @@ static noinline int __btrfs_run_delayed_refs(struct 
> btrfs_trans_handle *trans,
>   if (must_insert_reserved)
>   
> locked_ref->must_insert_reserved = 1;
>   locked_ref->processing = 0;
> + delayed_refs->num_heads_ready++;

I think this requires spin lock/unlock around the increment, as do other
similar places that fixup num_heads_ready after previous error.
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[PATCH] btrfs: fix error handling when run_delayed_extent_op fails

[Jeff Mahoney]

In __btrfs_run_delayed_refs, the error path when run_delayed_extent_op
fails sets locked_ref->processing = 0 but doesn't re-increment
delayed_refs->num_heads_ready.  As a result, we can end up triggering
the WARN_ON in btrfs_select_ref_head since the head remains in the tree
with ->processing = 0 and the ready count is off.

Fixes: d7df2c796d7 (Btrfs: attach delayed ref updates to delayed ref heads)
Reported-by: Jon Nelson 
Signed-off-by: Jeff Mahoney 
---
 fs/btrfs/extent-tree.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 4607af3..73a8d31 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -2588,6 +2588,7 @@ static noinline int __btrfs_run_delayed_refs(struct 
btrfs_trans_handle *trans,
if (must_insert_reserved)

locked_ref->must_insert_reserved = 1;
locked_ref->processing = 0;
+   delayed_refs->num_heads_ready++;
btrfs_debug(fs_info,
"run_delayed_extent_op 
returned %d",
ret);


-- 
Jeff Mahoney
SUSE Labs
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