Patchwork [10/29] jbd2: Fix race in t_outstanding_credits update in jbd2_journal_extend()

login
register
mail settings
Submitter Jan Kara
Date April 8, 2013, 9:32 p.m.
Message ID <1365456754-29373-11-git-send-email-jack@suse.cz>
Download mbox | patch
Permalink /patch/234896/
State Superseded
Headers show

Comments

Jan Kara - April 8, 2013, 9:32 p.m.
jbd2_journal_extend() first checked whether transaction can accept extending
handle with more credits and then added credits to t_outstanding_credits.
This can race with start_this_handle() adding another handle to a transaction
and thus overbooking a transaction. Make jbd2_journal_extend() use
atomic_add_return() to close the race.

Signed-off-by: Jan Kara <jack@suse.cz>
---
 fs/jbd2/transaction.c |    6 ++++--
 1 files changed, 4 insertions(+), 2 deletions(-)
Zheng Liu - May 5, 2013, 8:37 a.m.
On Mon, Apr 08, 2013 at 11:32:15PM +0200, Jan Kara wrote:
> jbd2_journal_extend() first checked whether transaction can accept extending
> handle with more credits and then added credits to t_outstanding_credits.
> This can race with start_this_handle() adding another handle to a transaction
> and thus overbooking a transaction. Make jbd2_journal_extend() use
> atomic_add_return() to close the race.
> 
> Signed-off-by: Jan Kara <jack@suse.cz>

Reviewed-by: Zheng Liu <wenqing.lz@taobao.com>
Regards,
                                                - Zheng

> ---
>  fs/jbd2/transaction.c |    6 ++++--
>  1 files changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
> index aee40c9..9639e47 100644
> --- a/fs/jbd2/transaction.c
> +++ b/fs/jbd2/transaction.c
> @@ -434,11 +434,13 @@ int jbd2_journal_extend(handle_t *handle, int nblocks)
>  	}
>  
>  	spin_lock(&transaction->t_handle_lock);
> -	wanted = atomic_read(&transaction->t_outstanding_credits) + nblocks;
> +	wanted = atomic_add_return(nblocks,
> +				   &transaction->t_outstanding_credits);
>  
>  	if (wanted > journal->j_max_transaction_buffers) {
>  		jbd_debug(3, "denied handle %p %d blocks: "
>  			  "transaction too large\n", handle, nblocks);
> +		atomic_sub(nblocks, &transaction->t_outstanding_credits);
>  		goto unlock;
>  	}
>  
> @@ -446,6 +448,7 @@ int jbd2_journal_extend(handle_t *handle, int nblocks)
>  	    jbd2_log_space_left(journal)) {
>  		jbd_debug(3, "denied handle %p %d blocks: "
>  			  "insufficient log space\n", handle, nblocks);
> +		atomic_sub(nblocks, &transaction->t_outstanding_credits);
>  		goto unlock;
>  	}
>  
> @@ -457,7 +460,6 @@ int jbd2_journal_extend(handle_t *handle, int nblocks)
>  
>  	handle->h_buffer_credits += nblocks;
>  	handle->h_requested_credits += nblocks;
> -	atomic_add(nblocks, &transaction->t_outstanding_credits);
>  	result = 0;
>  
>  	jbd_debug(3, "extended handle %p by %d\n", handle, nblocks);
> -- 
> 1.7.1
> 
> --
> To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Patch

diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
index aee40c9..9639e47 100644
--- a/fs/jbd2/transaction.c
+++ b/fs/jbd2/transaction.c
@@ -434,11 +434,13 @@  int jbd2_journal_extend(handle_t *handle, int nblocks)
 	}
 
 	spin_lock(&transaction->t_handle_lock);
-	wanted = atomic_read(&transaction->t_outstanding_credits) + nblocks;
+	wanted = atomic_add_return(nblocks,
+				   &transaction->t_outstanding_credits);
 
 	if (wanted > journal->j_max_transaction_buffers) {
 		jbd_debug(3, "denied handle %p %d blocks: "
 			  "transaction too large\n", handle, nblocks);
+		atomic_sub(nblocks, &transaction->t_outstanding_credits);
 		goto unlock;
 	}
 
@@ -446,6 +448,7 @@  int jbd2_journal_extend(handle_t *handle, int nblocks)
 	    jbd2_log_space_left(journal)) {
 		jbd_debug(3, "denied handle %p %d blocks: "
 			  "insufficient log space\n", handle, nblocks);
+		atomic_sub(nblocks, &transaction->t_outstanding_credits);
 		goto unlock;
 	}
 
@@ -457,7 +460,6 @@  int jbd2_journal_extend(handle_t *handle, int nblocks)
 
 	handle->h_buffer_credits += nblocks;
 	handle->h_requested_credits += nblocks;
-	atomic_add(nblocks, &transaction->t_outstanding_credits);
 	result = 0;
 
 	jbd_debug(3, "extended handle %p by %d\n", handle, nblocks);