linux-kernel - Re: [PATCH v2 4/4] lockdep: Assign a lock_class per gendisk used for wait_for

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Date:   Fri, 20 Oct 2017 07:44:51 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Byungchul Park <byungchul.park@....com>
Cc:     peterz@...radead.org, mingo@...nel.org, tglx@...utronix.de,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org, tj@...nel.org,
        johannes.berg@...el.com, oleg@...hat.com, amir73il@...il.com,
        david@...morbit.com, darrick.wong@...cle.com,
        linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-block@...r.kernel.org, hch@...radead.org, idryomov@...il.com,
        kernel-team@....com
Subject: Re: [PATCH v2 4/4] lockdep: Assign a lock_class per gendisk used for
 wait_for_completion()

The Subject prefix for this should be "block:".

> @@ -945,7 +945,7 @@ int submit_bio_wait(struct bio *bio)
>  {
>  	struct submit_bio_ret ret;
>  
> -	init_completion(&ret.event);
> +	init_completion_with_map(&ret.event, &bio->bi_disk->lockdep_map);

FYI, I have an outstanding patch to simplify this a lot, which
switches this to DECLARE_COMPLETION_ONSTACK.  I can delay this or let
you pick it up with your series, but we'll need a variant of
DECLARE_COMPLETION_ONSTACK with the lockdep annotations.

Patch below for reference:

---
>From d65b89843c9f82c0744643515ba51dd10e66e67b Mon Sep 17 00:00:00 2001
From: Christoph Hellwig <hch@....de>
Date: Thu, 5 Oct 2017 18:31:02 +0200
Subject: block: use DECLARE_COMPLETION_ONSTACK in submit_bio_wait

Simplify the code by getting rid of the submit_bio_ret structure.

Signed-off-by: Christoph Hellwig <hch@....de>
---
 block/bio.c | 19 +++++--------------
 1 file changed, 5 insertions(+), 14 deletions(-)

diff --git a/block/bio.c b/block/bio.c
index 8338304ea256..4e18e959fc0a 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -917,17 +917,9 @@ int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
 }
 EXPORT_SYMBOL_GPL(bio_iov_iter_get_pages);
 
-struct submit_bio_ret {
-	struct completion event;
-	int error;
-};
-
 static void submit_bio_wait_endio(struct bio *bio)
 {
-	struct submit_bio_ret *ret = bio->bi_private;
-
-	ret->error = blk_status_to_errno(bio->bi_status);
-	complete(&ret->event);
+	complete(bio->bi_private);
 }
 
 /**
@@ -943,16 +935,15 @@ static void submit_bio_wait_endio(struct bio *bio)
  */
 int submit_bio_wait(struct bio *bio)
 {
-	struct submit_bio_ret ret;
+	DECLARE_COMPLETION_ONSTACK(done);
 
-	init_completion(&ret.event);
-	bio->bi_private = &ret;
+	bio->bi_private = &done;
 	bio->bi_end_io = submit_bio_wait_endio;
 	bio->bi_opf |= REQ_SYNC;
 	submit_bio(bio);
-	wait_for_completion_io(&ret.event);
+	wait_for_completion_io(&done);
 
-	return ret.error;
+	return blk_status_to_errno(bio->bi_status);
 }
 EXPORT_SYMBOL(submit_bio_wait);
 
-- 
2.14.2