On Thu, Dec 21, 2023 at 03:36:40AM +0000, Ed Tsai (蔡宗軒) wrote: > On Wed, 2023-12-20 at 17:27 -0800, Song Liu wrote: > > > > External email : Please do not click links or open attachments until > > you have verified the sender or the content. > > A recent bug report [1] shows md is handling a flush from bcachefs > > as read: > > > > bch2_journal_write=> > > submit_bio=> > > ... > > md_handle_request => > > raid5_make_request => > > chunk_aligned_read => > > raid5_read_one_chunk => > > ... > > > > It appears md code only checks REQ_PREFLUSH for flush requests, which > > doesn't cover all cases. OTOH, op_is_flush() doesn't check > > REQ_OP_FLUSH > > either. > > > > Fix this by: > > 1) Check REQ_PREFLUSH in op_is_flush(); > > 2) Use op_is_flush() in md code. > > > > Thanks, > > Song > > > > [1] > > https://urldefense.com/v3/__https://bugzilla.kernel.org/show_bug.cgi?id=218184__;!!CTRNKA9wMg0ARbw!gQbjtS_f5d3Du2prpIT8zUM4mkZf7qDleyaAuEfG8j5tMrDvw7cfJUB04VWl0uVAL4BJ4YWbVopp$ > > > > REQ_OP_FLUSH is only used by the block layer's flush code, and the > filesystem should use REQ_PREFLUSH with an empty write bio. > > If we want upper layer to be able to directly send REQ_OP_FLUSH bio, > then we should retrieve all REQ_PREFLUSH to confirm. At least for now, > it seems that REQ_OP_FLUSH without REQ_PREFLUSH in `blk_flush_policy` > will directly return 0 and no flush operation will be sent to the > driver. If that's the case, then it should be documented and there should be a WARN_ON() in generic_make_request(). Also, glancing at blk_types.h, we have the req_op and req_flag_bits both using (__force blk_opf_t), but using the same bit range - what the hell? That's seriously broken...
