linux-kernel - [PATCH 5.8 169/255] block: loop: set discard granularity and alignment for block device backed loop

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Message-Id: <20200901151008.792032374@linuxfoundation.org>
Date:   Tue,  1 Sep 2020 17:10:25 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Ming Lei <ming.lei@...hat.com>,
        Christoph Hellwig <hch@....de>, Coly Li <colyli@...e.de>,
        Hannes Reinecke <hare@...e.com>, Xiao Ni <xni@...hat.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Evan Green <evgreen@...omium.org>,
        Gwendal Grignou <gwendal@...omium.org>,
        Chaitanya Kulkarni <chaitanya.kulkarni@....com>,
        Andrzej Pietrasiewicz <andrzej.p@...labora.com>,
        Jens Axboe <axboe@...nel.dk>
Subject: [PATCH 5.8 169/255] block: loop: set discard granularity and alignment for block device backed loop

From: Ming Lei <ming.lei@...hat.com>

commit bcb21c8cc9947286211327d663ace69f07d37a76 upstream.

In case of block device backend, if the backend supports write zeros, the
loop device will set queue flag of QUEUE_FLAG_DISCARD. However,
limits.discard_granularity isn't setup, and this way is wrong,
see the following description in Documentation/ABI/testing/sysfs-block:

	A discard_granularity of 0 means that the device does not support
	discard functionality.

Especially 9b15d109a6b2 ("block: improve discard bio alignment in
__blkdev_issue_discard()") starts to take q->limits.discard_granularity
for computing max discard sectors. And zero discard granularity may cause
kernel oops, or fail discard request even though the loop queue claims
discard support via QUEUE_FLAG_DISCARD.

Fix the issue by setup discard granularity and alignment.

Fixes: c52abf563049 ("loop: Better discard support for block devices")
Signed-off-by: Ming Lei <ming.lei@...hat.com>
Reviewed-by: Christoph Hellwig <hch@....de>
Acked-by: Coly Li <colyli@...e.de>
Cc: Hannes Reinecke <hare@...e.com>
Cc: Xiao Ni <xni@...hat.com>
Cc: Martin K. Petersen <martin.petersen@...cle.com>
Cc: Evan Green <evgreen@...omium.org>
Cc: Gwendal Grignou <gwendal@...omium.org>
Cc: Chaitanya Kulkarni <chaitanya.kulkarni@....com>
Cc: Andrzej Pietrasiewicz <andrzej.p@...labora.com>
Cc: Christoph Hellwig <hch@....de>
Cc: <stable@...r.kernel.org>
Signed-off-by: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/block/loop.c |   33 ++++++++++++++++++---------------
 1 file changed, 18 insertions(+), 15 deletions(-)

--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -877,6 +877,7 @@ static void loop_config_discard(struct l
 	struct file *file = lo->lo_backing_file;
 	struct inode *inode = file->f_mapping->host;
 	struct request_queue *q = lo->lo_queue;
+	u32 granularity, max_discard_sectors;
 
 	/*
 	 * If the backing device is a block device, mirror its zeroing
@@ -889,11 +890,10 @@ static void loop_config_discard(struct l
 		struct request_queue *backingq;
 
 		backingq = bdev_get_queue(inode->i_bdev);
-		blk_queue_max_discard_sectors(q,
-			backingq->limits.max_write_zeroes_sectors);
 
-		blk_queue_max_write_zeroes_sectors(q,
-			backingq->limits.max_write_zeroes_sectors);
+		max_discard_sectors = backingq->limits.max_write_zeroes_sectors;
+		granularity = backingq->limits.discard_granularity ?:
+			queue_physical_block_size(backingq);
 
 	/*
 	 * We use punch hole to reclaim the free space used by the
@@ -902,23 +902,26 @@ static void loop_config_discard(struct l
 	 * useful information.
 	 */
 	} else if (!file->f_op->fallocate || lo->lo_encrypt_key_size) {
-		q->limits.discard_granularity = 0;
-		q->limits.discard_alignment = 0;
-		blk_queue_max_discard_sectors(q, 0);
-		blk_queue_max_write_zeroes_sectors(q, 0);
+		max_discard_sectors = 0;
+		granularity = 0;
 
 	} else {
-		q->limits.discard_granularity = inode->i_sb->s_blocksize;
-		q->limits.discard_alignment = 0;
-
-		blk_queue_max_discard_sectors(q, UINT_MAX >> 9);
-		blk_queue_max_write_zeroes_sectors(q, UINT_MAX >> 9);
+		max_discard_sectors = UINT_MAX >> 9;
+		granularity = inode->i_sb->s_blocksize;
 	}
 
-	if (q->limits.max_write_zeroes_sectors)
+	if (max_discard_sectors) {
+		q->limits.discard_granularity = granularity;
+		blk_queue_max_discard_sectors(q, max_discard_sectors);
+		blk_queue_max_write_zeroes_sectors(q, max_discard_sectors);
 		blk_queue_flag_set(QUEUE_FLAG_DISCARD, q);
-	else
+	} else {
+		q->limits.discard_granularity = 0;
+		blk_queue_max_discard_sectors(q, 0);
+		blk_queue_max_write_zeroes_sectors(q, 0);
 		blk_queue_flag_clear(QUEUE_FLAG_DISCARD, q);
+	}
+	q->limits.discard_alignment = 0;
 }
 
 static void loop_unprepare_queue(struct loop_device *lo)