On Thu 27-01-22 10:49:42, Christoph Hellwig wrote:
> On Thu, Jan 27, 2022 at 10:47:37AM +0100, Jan Kara wrote:
> > On Wed 26-01-22 16:50:35, Christoph Hellwig wrote:
> > > Nothing prevents a file system or userspace opener of the block device
> > > from redirtying the page right afte sync_blockdev returned. Fortunately
> > > data in the page cache during a block device change is mostly harmless
> > > anyway.
> > >
> > > Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> >
> > My understanding was these warnings are there to tell userspace it is doing
> > something wrong. Something like the warning we issue when DIO races with
> > buffered IO... I'm not sure how useful they are but I don't see strong
> > reason to remove them either...
>
> Well, it is not just a warning, but also fails the command. With some of
> the reduced synchronization blktests loop/002 can hit them pretty reliably.
I see. I guess another place where using mapping->invalidate_lock would be
good to avoid these races... So maybe something like attached patch?
Honza
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
>From 3914760aa538f55012f41859857cfe75bdcfc6a2 Mon Sep 17 00:00:00 2001
From: Jan Kara <jack@xxxxxxx>
Date: Thu, 27 Jan 2022 12:43:26 +0100
Subject: [PATCH] loop: Protect loop device invalidation from racing page cache
operations
Grab bdev->i_mutex and bdev->i_mapping->invalidate_lock to protect
operations invalidating loop device page cache from racing operations on
the page cache. As a result we can drop some warnings.
Signed-off-by: Jan Kara <jack@xxxxxxx>
---
drivers/block/loop.c | 29 ++++++++---------------------
1 file changed, 8 insertions(+), 21 deletions(-)
diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 01cbbfc4e9e2..170e3dc0d8a9 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -1252,6 +1252,8 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
if (lo->lo_offset != info->lo_offset ||
lo->lo_sizelimit != info->lo_sizelimit) {
size_changed = true;
+ inode_lock(lo->lo_device->bd_inode);
+ filemap_invalidate_lock(lo->lo_device->bd_inode->i_mapping);
sync_blockdev(lo->lo_device);
invalidate_bdev(lo->lo_device);
}
@@ -1259,15 +1261,6 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
/* I/O need to be drained during transfer transition */
blk_mq_freeze_queue(lo->lo_queue);
- if (size_changed && lo->lo_device->bd_inode->i_mapping->nrpages) {
- /* If any pages were dirtied after invalidate_bdev(), try again */
- err = -EAGAIN;
- pr_warn("%s: loop%d (%s) has still dirty pages (nrpages=%lu)\n",
- __func__, lo->lo_number, lo->lo_file_name,
- lo->lo_device->bd_inode->i_mapping->nrpages);
- goto out_unfreeze;
- }
-
prev_lo_flags = lo->lo_flags;
err = loop_set_status_from_info(lo, info);
@@ -1285,6 +1278,8 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
loff_t new_size = get_size(lo->lo_offset, lo->lo_sizelimit,
lo->lo_backing_file);
loop_set_size(lo, new_size);
+ filemap_invalidate_unlock(lo->lo_device->bd_inode->i_mapping);
+ inode_unlock(lo->lo_device->bd_inode);
}
loop_config_discard(lo);
@@ -1474,26 +1469,18 @@ static int loop_set_block_size(struct loop_device *lo, unsigned long arg)
if (lo->lo_queue->limits.logical_block_size == arg)
return 0;
+ inode_lock(lo->lo_device->bd_inode);
+ filemap_invalidate_lock(lo->lo_device->bd_inode->i_mapping);
sync_blockdev(lo->lo_device);
invalidate_bdev(lo->lo_device);
-
blk_mq_freeze_queue(lo->lo_queue);
-
- /* invalidate_bdev should have truncated all the pages */
- if (lo->lo_device->bd_inode->i_mapping->nrpages) {
- err = -EAGAIN;
- pr_warn("%s: loop%d (%s) has still dirty pages (nrpages=%lu)\n",
- __func__, lo->lo_number, lo->lo_file_name,
- lo->lo_device->bd_inode->i_mapping->nrpages);
- goto out_unfreeze;
- }
-
blk_queue_logical_block_size(lo->lo_queue, arg);
blk_queue_physical_block_size(lo->lo_queue, arg);
blk_queue_io_min(lo->lo_queue, arg);
loop_update_dio(lo);
-out_unfreeze:
blk_mq_unfreeze_queue(lo->lo_queue);
+ filemap_invalidate_unlock(lo->lo_device->bd_inode->i_mapping);
+ inode_unlock(lo->lo_device->bd_inode);
return err;
}
--
2.31.1
