linux-kernel - [PATCH AUTOSEL 5.15 10/28] block: loop:use kstatfs.f_bsize of backing file to set discard granularity

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Date:   Tue, 22 Feb 2022 21:29:11 -0500
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Ming Lei <ming.lei@...hat.com>, Christoph Hellwig <hch@....de>,
        Vivek Goyal <vgoyal@...hat.com>,
        Pei Zhang <pezhang@...hat.com>, Jens Axboe <axboe@...nel.dk>,
        Sasha Levin <sashal@...nel.org>, linux-block@...r.kernel.org
Subject: [PATCH AUTOSEL 5.15 10/28] block: loop:use kstatfs.f_bsize of backing file to set discard granularity

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

[ Upstream commit 06582bc86d7f48d35cd044098ca1e246e8c7c52e ]

If backing file's filesystem has implemented ->fallocate(), we think the
loop device can support discard, then pass sb->s_blocksize as
discard_granularity. However, some underlying FS, such as overlayfs,
doesn't set sb->s_blocksize, and causes discard_granularity to be set as
zero, then the warning in __blkdev_issue_discard() is triggered.

Christoph suggested to pass kstatfs.f_bsize as discard granularity, and
this way is fine because kstatfs.f_bsize means 'Optimal transfer block
size', which still matches with definition of discard granularity.

So fix the issue by setting discard_granularity as kstatfs.f_bsize if it
is available, otherwise claims discard isn't supported.

Cc: Christoph Hellwig <hch@....de>
Cc: Vivek Goyal <vgoyal@...hat.com>
Reported-by: Pei Zhang <pezhang@...hat.com>
Signed-off-by: Ming Lei <ming.lei@...hat.com>
Reviewed-by: Christoph Hellwig <hch@....de>
Link: https://lore.kernel.org/r/20220126035830.296465-1-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/block/loop.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index c00ae30fde89e..92f9d32bfae5e 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -79,6 +79,7 @@
 #include <linux/ioprio.h>
 #include <linux/blk-cgroup.h>
 #include <linux/sched/mm.h>
+#include <linux/statfs.h>
 
 #include "loop.h"
 
@@ -939,8 +940,13 @@ static void loop_config_discard(struct loop_device *lo)
 		granularity = 0;
 
 	} else {
+		struct kstatfs sbuf;
+
 		max_discard_sectors = UINT_MAX >> 9;
-		granularity = inode->i_sb->s_blocksize;
+		if (!vfs_statfs(&file->f_path, &sbuf))
+			granularity = sbuf.f_bsize;
+		else
+			max_discard_sectors = 0;
 	}
 
 	if (max_discard_sectors) {
-- 
2.34.1