diff options
| -rw-r--r-- | fs/xfs/xfs_buf_item.c | 28 |
1 files changed, 21 insertions, 7 deletions
diff --git a/fs/xfs/xfs_buf_item.c b/fs/xfs/xfs_buf_item.c index 12d8455bfbb2..010db5f8fb00 100644 --- a/fs/xfs/xfs_buf_item.c +++ b/fs/xfs/xfs_buf_item.c @@ -1233,9 +1233,23 @@ xfs_buf_iodone( } /* - * Requeue a failed buffer for writeback + * Requeue a failed buffer for writeback. * - * Return true if the buffer has been re-queued properly, false otherwise + * We clear the log item failed state here as well, but we have to be careful + * about reference counts because the only active reference counts on the buffer + * may be the failed log items. Hence if we clear the log item failed state + * before queuing the buffer for IO we can release all active references to + * the buffer and free it, leading to use after free problems in + * xfs_buf_delwri_queue. It makes no difference to the buffer or log items which + * order we process them in - the buffer is locked, and we own the buffer list + * so nothing on them is going to change while we are performing this action. + * + * Hence we can safely queue the buffer for IO before we clear the failed log + * item state, therefore always having an active reference to the buffer and + * avoiding the transient zero-reference state that leads to use-after-free. + * + * Return true if the buffer was added to the buffer list, false if it was + * already on the buffer list. */ bool xfs_buf_resubmit_failed_buffers( @@ -1243,16 +1257,16 @@ xfs_buf_resubmit_failed_buffers( struct list_head *buffer_list) { struct xfs_log_item *lip; + bool ret; + + ret = xfs_buf_delwri_queue(bp, buffer_list); /* - * Clear XFS_LI_FAILED flag from all items before resubmit - * - * XFS_LI_FAILED set/clear is protected by ail_lock, caller this + * XFS_LI_FAILED set/clear is protected by ail_lock, caller of this * function already have it acquired */ list_for_each_entry(lip, &bp->b_li_list, li_bio_list) xfs_clear_li_failed(lip); - /* Add this buffer back to the delayed write list */ - return xfs_buf_delwri_queue(bp, buffer_list); + return ret; } |