linux-kernel - Re: IO errors after "block: remove bio_get_nr

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Date:	Tue, 22 Dec 2015 05:26:12 +0000
From:	Junichi Nomura <j-nomura@...jp.nec.com>
To:	Kent Overstreet <kent.overstreet@...il.com>,
	Tejun Heo <tj@...nel.org>
CC:	"Artem S. Tashkinov" <t.artem@...os.com>,
	"Artem S. Tashkinov" <t.artem@...lcity.com>,
	Christoph Hellwig <hch@....de>,
	Ming Lin <ming.l@....samsung.com>, Jens Axboe <axboe@...com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Steven Whitehouse <swhiteho@...hat.com>,
	IDE-ML <linux-ide@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Ming Lei <tom.leiming@...il.com>
Subject: Re: IO errors after "block: remove bio_get_nr_vecs()"

On 12/22/15 12:59, Kent Overstreet wrote:
> reproduced it with 32 bit pae:
> 
>> 1. Exclude memory above 4G line with boot param "max_addr=4G".
> 
> doesn't work - max_addr=1G doesn't work either
> 
>> 2. Disable highmem with "highmem=0".
> 
> works!
> 
>> 3. Try booting 64bit kernel.
> 
> works

blk_queue_bio() does split then bounce, which makes the segment
counting based on pages before bouncing and could go wrong.

What do you think of a patch like this?

-- 
Jun'ichi Nomura, NEC Corporation

diff --git a/block/blk-core.c b/block/blk-core.c
index 5131993b..1d1c3c7 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1689,8 +1689,6 @@ static blk_qc_t blk_queue_bio(struct request_queue *q, struct bio *bio)
 	struct request *req;
 	unsigned int request_count = 0;
 
-	blk_queue_split(q, &bio, q->bio_split);
-
 	/*
 	 * low level driver can indicate that it wants pages above a
 	 * certain limit bounced to low memory (ie for highmem, or even
@@ -1698,6 +1696,8 @@ static blk_qc_t blk_queue_bio(struct request_queue *q, struct bio *bio)
 	 */
 	blk_queue_bounce(q, &bio);
 
+	blk_queue_split(q, &bio, q->bio_split);
+
 	if (bio_integrity_enabled(bio) && bio_integrity_prep(bio)) {
 		bio->bi_error = -EIO;
 		bio_endio(bio);--
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