linux-kernel - Re: false positive lockdep splat with loop device

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Message-ID: <20171005163328.GA3562@infradead.org>
Date:   Thu, 5 Oct 2017 09:33:28 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Amir Goldstein <amir73il@...il.com>
Cc:     Dave Chinner <david@...morbit.com>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        xfs <linux-xfs@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Byungchul Park <byungchul.park@....com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        linux-block <linux-block@...r.kernel.org>
Subject: Re: false positive lockdep splat with loop device

Does the patch below fix the warning for you?

--
>From 28aae7104425433d39e6142adcd5b88dc5b0ad5f 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

This way we get our lockdep annotations right in case multiple layers
in the stack use submit_bio_wait.

It also happens to 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);
 
-- 
2.14.1