On Fri, Feb 19, 2016 at 04:59:41PM +0100, Jan Kara wrote: > When mapping blocks for direct IO, we allocate io_end structure before > mapping blocks and store pointer to it in the inode. This creates a > requirement that any AIO DIO using io_end must be protected by i_mutex. > This created problems in the past with dioread_nolock mode which was > corrupting io_end pointers. Also io_end is allocated unnecessarily in > case where we don't need to convert any extents (which is a common case > for example when overwriting file). > > We fix the problem by allocating io_end only once we return unwritten > extent from block mapping function for AIO DIO (so we can save some > pointless io_end allocations) and we pass pointer to it in bh->b_private > which generic DIO code later passes to our end IO callback. That way we > remove any need for global pointer to io_end structure and thus fix the > races. > > The downside of this change is that the checking for unwritten IO in > flight in ext4_extents_can_be_merged() is more racy since we now > increment i_unwritten / set EXT4_STATE_DIO_UNWRITTEN only after dropping > i_data_sem. However the check has been racy already before because > ext4_writepages() already increment i_unwritten after dropping > i_data_sem and reserved blocks save us from hitting ENOSPC in the worst > case. > > Signed-off-by: Jan Kara <jack@xxxxxxx> Thanks, applied. - Ted -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
