Currently only dm and md/raid5 bios trigger trace_block_bio_complete(). Now that we have bio_chain() and bio_inc_remaining(), it is not possible, in general, for a driver to know when the bio is really complete. Only bio_endio() knows that. So move the trace_block_bio_complete() call to bio_endio(). Now trace_block_bio_complete() pairs with trace_block_bio_queue(). Any bio for which a 'queue' event is traced, will subsequently generate a 'complete' event. There are a few cases where completion tracing is not wanted. 1/ If blk_update_request() has already generated a completion trace event at the 'request' level, there is no point generating one at the bio level too. In this case the bi_sector and bi_size will have changed, so the bio level event would be wrong 2/ If the bio hasn't actually been queued yet, but is being aborted early, then a trace event could be confusing. Some filesystems call bio_endio() but do not want tracing. 3/ The bio_integrity code interposes itself by replacing bi_end_io, then restoring it and calling bio_endio() again. This would produce two identical trace events if left like that. To handle these, we introduce a flag BIO_TRACE_COMPLETION and only produce the trace event when this is set. We address point 1 above by clearing the flag in blk_update_request(). We address point 2 above by only setting the flag when generic_make_request() is called. We address point 3 above by clearing the flag after generating a completion event. When bio_split() is used on a bio, particularly in blk_queue_split(), there is an extra complication. A new bio is split off the front, and may be handle directly without going through generic_make_request(). The old bio, which has been advanced, is passed to generic_make_request(), so it will trigger a trace event a second time. Probably the best result when a split happens is to see a single 'queue' event for the whole bio, then multiple 'complete' events - one for each component. To achieve this was can: - copy the BIO_TRACE_COMPLETION flag to the new bio in bio_split() - avoid generating a 'queue' event if BIO_TRACE_COMPLETION is already set. This way, the split-off bio won't create a queue event, the original won't either even if it re-submitted to generic_make_request(), but both will produce completion events, each for their own range. So if generic_make_request() is called (which generates a QUEUED event), then bi_endio() will create a single COMPLETE event for each range that the bio is split into, unless the driver has explicitly requested it not to. Signed-off-by: NeilBrown --- block/bio.c | 13 +++++++++++++ block/blk-core.c | 10 +++++++++- drivers/md/dm.c | 1 - drivers/md/raid5.c | 8 -------- include/linux/blk_types.h | 4 +++- 5 files changed, 25 insertions(+), 11 deletions(-) diff --git a/block/bio.c b/block/bio.c index 5eec5e08417f..c1272986133e 100644 --- a/block/bio.c +++ b/block/bio.c @@ -1818,6 +1818,11 @@ static inline bool bio_remaining_done(struct bio *bio) * bio_endio() will end I/O on the whole bio. bio_endio() is the preferred * way to end I/O on a bio. No one should call bi_end_io() directly on a * bio unless they own it and thus know that it has an end_io function. + * + * bio_endio() can be called several times on a bio that has been chained + * using bio_chain(). The ->bi_end_io() function will only be call the + * last time. At this point the BLK_TA_COMPLETE tracing event will be + * generated if BIO_TRACE_COMPLETION is set. **/ void bio_endio(struct bio *bio) { @@ -1838,6 +1843,11 @@ void bio_endio(struct bio *bio) goto again; } + if (bio->bi_bdev && bio_flagged(bio, BIO_TRACE_COMPLETION)) { + trace_block_bio_complete(bdev_get_queue(bio->bi_bdev), + bio, bio->bi_error); + bio_clear_flag(bio, BIO_TRACE_COMPLETION); + } if (bio->bi_end_io) bio->bi_end_io(bio); } @@ -1876,6 +1886,9 @@ struct bio *bio_split(struct bio *bio, int sectors, bio_advance(bio, split->bi_iter.bi_size); + if (bio_flagged(bio, BIO_TRACE_COMPLETION)) + bio_set_flag(bio, BIO_TRACE_COMPLETION); + return split; } EXPORT_SYMBOL(bio_split); diff --git a/block/blk-core.c b/block/blk-core.c index 0eeb99ef654f..b34b5b1b1bbf 100644 --- a/block/blk-core.c +++ b/block/blk-core.c @@ -1936,7 +1936,13 @@ generic_make_request_checks(struct bio *bio) if (!blkcg_bio_issue_check(q, bio)) return false; - trace_block_bio_queue(q, bio); + if (!bio_flagged(bio, BIO_TRACE_COMPLETION)) { + trace_block_bio_queue(q, bio); + /* Now that enqueuing has been traced, we need to trace + * completion as well. + */ + bio_set_flag(bio, BIO_TRACE_COMPLETION); + } return true; not_supported: @@ -2595,6 +2601,8 @@ bool blk_update_request(struct request *req, int error, unsigned int nr_bytes) if (bio_bytes == bio->bi_iter.bi_size) req->bio = bio->bi_next; + /* Completion has already been traced */ + bio_clear_flag(bio, BIO_TRACE_COMPLETION); req_bio_endio(req, bio, bio_bytes, error); total_bytes += bio_bytes; diff --git a/drivers/md/dm.c b/drivers/md/dm.c index f4ffd1eb8f44..f5f09ace690a 100644 --- a/drivers/md/dm.c +++ b/drivers/md/dm.c @@ -810,7 +810,6 @@ static void dec_pending(struct dm_io *io, int error) queue_io(md, bio); } else { /* done with normal IO or empty flush */ - trace_block_bio_complete(md->queue, bio, io_error); bio->bi_error = io_error; bio_endio(bio); } diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c index 9a3b7da34137..f684cb566721 100644 --- a/drivers/md/raid5.c +++ b/drivers/md/raid5.c @@ -5141,8 +5141,6 @@ static void raid5_align_endio(struct bio *bi) rdev_dec_pending(rdev, conf->mddev); if (!error) { - trace_block_bio_complete(bdev_get_queue(raid_bi->bi_bdev), - raid_bi, 0); bio_endio(raid_bi); if (atomic_dec_and_test(&conf->active_aligned_reads)) wake_up(&conf->wait_for_quiescent); @@ -5727,10 +5725,6 @@ static void raid5_make_request(struct mddev *mddev, struct bio * bi) md_write_end(mddev); remaining = raid5_dec_bi_active_stripes(bi); if (remaining == 0) { - - - trace_block_bio_complete(bdev_get_queue(bi->bi_bdev), - bi, 0); bio_endio(bi); } } @@ -6138,8 +6132,6 @@ static int retry_aligned_read(struct r5conf *conf, struct bio *raid_bio) } remaining = raid5_dec_bi_active_stripes(raid_bio); if (remaining == 0) { - trace_block_bio_complete(bdev_get_queue(raid_bio->bi_bdev), - raid_bio, 0); bio_endio(raid_bio); } if (atomic_dec_and_test(&conf->active_aligned_reads)) diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h index d703acb55d0f..db7a57ee0e58 100644 --- a/include/linux/blk_types.h +++ b/include/linux/blk_types.h @@ -29,7 +29,7 @@ struct bio { * top bits REQ_OP. Use * accessors. */ - unsigned short bi_flags; /* status, command, etc */ + unsigned short bi_flags; /* status, etc */ unsigned short bi_ioprio; struct bvec_iter bi_iter; @@ -102,6 +102,8 @@ struct bio { #define BIO_REFFED 8 /* bio has elevated ->bi_cnt */ #define BIO_THROTTLED 9 /* This bio has already been subjected to * throttling rules. Don't do it again. */ +#define BIO_TRACE_COMPLETION 10 /* bio_endio() should trace the final completion + * of this bio. */ /* * Flags starting here get preserved by bio_reset() - this includes -- 2.12.0