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Message-ID: <87shm4a4lt.fsf@notabene.neil.brown.name>
Date: Thu, 23 Mar 2017 17:29:02 +1100
From: NeilBrown <neilb@...e.com>
To: Christoph Hellwig <hch@...radead.org>, Jens Axboe <axboe@...nel.dk>
Cc: linux-block@...r.kernel.org, linux-raid@...r.kernel.org,
dm-devel@...hat.com, Alasdair Kergon <agk@...hat.com>,
Mike Snitzer <snitzer@...hat.com>,
Shaohua Li <shli@...nel.org>, linux-kernel@...r.kernel.org,
Martin K "." Petersen <martin.petersen@...cle.com>
Subject: [PATCH v2] block: trace completion of all bios.
Currently only dm and md/raid5 bios trigger trace_block_bio_complete().
Now that we have bio_chain(), 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() and will need to use a different interface to
avoid tracing
3/ The bio_integrity code interposes itself by replacing bi_end_io,
then restores it and calls bio_endio() again. This would produce
two identical trace events if left like that.
To handle these, we provide bio_endio_notrace(). This patch only adds
uses of this in core code. Separate patches will be needed to update
the filesystems to avoid tracing.
Signed-off-by: NeilBrown <neilb@...e.com>
---
block/bio-integrity.c | 4 ++--
block/bio.c | 46 ++++++++++++++++++++++++++++++++++++++++++++++
block/blk-core.c | 2 +-
drivers/md/dm.c | 1 -
drivers/md/raid5.c | 8 --------
include/linux/bio.h | 1 +
6 files changed, 50 insertions(+), 12 deletions(-)
diff --git a/block/bio-integrity.c b/block/bio-integrity.c
index 5384713d48bc..28581e2f68fb 100644
--- a/block/bio-integrity.c
+++ b/block/bio-integrity.c
@@ -370,7 +370,7 @@ static void bio_integrity_verify_fn(struct work_struct *work)
/* Restore original bio completion handler */
bio->bi_end_io = bip->bip_end_io;
- bio_endio(bio);
+ bio_endio_notrace(bio);
}
/**
@@ -397,7 +397,7 @@ void bio_integrity_endio(struct bio *bio)
*/
if (bio->bi_error) {
bio->bi_end_io = bip->bip_end_io;
- bio_endio(bio);
+ bio_endio_notrace(bio);
return;
}
diff --git a/block/bio.c b/block/bio.c
index 5eec5e08417f..c8e5d24abd52 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -1811,6 +1811,45 @@ static inline bool bio_remaining_done(struct bio *bio)
}
/**
+ * bio_endio_notrace - end I/O on a bio without tracing
+ * @bio: bio
+ *
+ * Description:
+ * bio_endio_notrace() will end I/O on the whole bio.
+ * bio_endio_notrace() should only be call if a completion trace
+ * event is not needed. This can be the case if a request-level
+ * completion event has already been generated, if the bio is
+ * being completed early, before it was even queued.
+ *
+ **/
+void bio_endio_notrace(struct bio *bio)
+{
+again:
+ if (!bio_remaining_done(bio))
+ return;
+
+ /*
+ * Need to have a real endio function for chained bios, otherwise
+ * various corner cases will break (like stacking block devices that
+ * save/restore bi_end_io) - however, we want to avoid unbounded
+ * recursion and blowing the stack. Tail call optimization would
+ * handle this, but compiling with frame pointers also disables
+ * gcc's sibling call optimization.
+ */
+ if (bio->bi_end_io == bio_chain_endio) {
+ bio = __bio_chain_endio(bio);
+ goto again;
+ }
+
+ if (bio->bi_bdev)
+ trace_block_bio_complete(bdev_get_queue(bio->bi_bdev),
+ bio, bio->bi_error);
+ if (bio->bi_end_io)
+ bio->bi_end_io(bio);
+}
+EXPORT_SYMBOL(bio_endio_notrace);
+
+/**
* bio_endio - end I/O on a bio
* @bio: bio
*
@@ -1818,6 +1857,10 @@ 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
+ * time. At this point the BLK_TA_COMPLETE tracing event will be generated.
**/
void bio_endio(struct bio *bio)
{
@@ -1838,6 +1881,9 @@ void bio_endio(struct bio *bio)
goto again;
}
+ if (bio->bi_bdev)
+ trace_block_bio_complete(bdev_get_queue(bio->bi_bdev),
+ bio, bio->bi_error);
if (bio->bi_end_io)
bio->bi_end_io(bio);
}
diff --git a/block/blk-core.c b/block/blk-core.c
index 0eeb99ef654f..b6c76580a796 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -142,7 +142,7 @@ static void req_bio_endio(struct request *rq, struct bio *bio,
/* don't actually finish bio if it's part of flush sequence */
if (bio->bi_iter.bi_size == 0 && !(rq->rq_flags & RQF_FLUSH_SEQ))
- bio_endio(bio);
+ bio_endio_notrace(bio);
}
void blk_dump_rq_flags(struct request *rq, char *msg)
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/bio.h b/include/linux/bio.h
index 8e521194f6fc..e0552bee227b 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -418,6 +418,7 @@ static inline struct bio *bio_clone_kmalloc(struct bio *bio, gfp_t gfp_mask)
extern blk_qc_t submit_bio(struct bio *);
extern void bio_endio(struct bio *);
+extern void bio_endio_notrace(struct bio *);
static inline void bio_io_error(struct bio *bio)
{
--
2.12.0
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