block: loop:use kstatfs.f_bsize of backing file to set discard granularity

[ 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@lst.de>
Cc: Vivek Goyal <vgoyal@redhat.com>
Reported-by: Pei Zhang <pezhang@redhat.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20220126035830.296465-1-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index c00ae30..92f9d32 100644 (file)
--- 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) {