On 11/26, Bart Van Assche wrote:
> On 11/26/19 10:29 AM, Jaegeuk Kim wrote:
> > On 11/25, Bart Van Assche wrote:
> > > diff --git a/drivers/block/loop.c b/drivers/block/loop.c
> > > index 739b372a5112..84bdb3a6f6d0 100644
> > > --- a/drivers/block/loop.c
> > > +++ b/drivers/block/loop.c
> > > @@ -1264,14 +1264,17 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
> > > goto out_unlock;
> > > }
> > >
> > > - if (lo->lo_offset != info->lo_offset ||
> > > - lo->lo_sizelimit != info->lo_sizelimit) {
> > > - sync_blockdev(lo->lo_device);
> > > - kill_bdev(lo->lo_device);
> > > - }
> > > + /*
> > > + * Drain the page cache and the request queue. Set the "dying" flag to
> > > + * prevent that kill_bdev() locks up.
> > > + */
> > > + sync_blockdev(lo->lo_device);
> > >
> > > - /* I/O need to be drained during transfer transition */
> > > - blk_mq_freeze_queue(lo->lo_queue);
> > > + blk_set_queue_dying(lo->lo_queue);
> > > + blk_mq_freeze_queue_wait(lo->lo_queue);
> > > +
> > > + /* Kill buffers that got dirtied after the sync_blockdev() call. */
> >
> > Any race condition where we can truncate any dirty pages written between
> > sync_blockdev() and kill_bdev()?
> >
> > Thanks,
> >
> > > + kill_bdev(lo->lo_device);
>
> Hi Jaegeuk,
>
> As you know sync_blockdev() triggers a call to filemap_write_and_wait().
> That function in turn calls mapping->a_ops->writepages() with sync_mode ==
> WB_SYNC_ALL. I think that causes sync_blockdev() to wait until all dirty
> pages have been written so we don't have to worry about pages dirtied before
> the sync_blockdev() call started.
My concern is on some dirty pages after sync_blockdev(), since
truncate_inode_pages() in kill_bdev() will cancel dirty pages.
>
> Should we try to handle read and write requests that are submitted to a loop
> device while the loop device block size, offset and/or size are being
> modified or is it OK to fail such requests? The blk_set_queue_dying() and
> blk_mq_freeze_queue_wait() calls set the DYING queue flag and also wait for
> all ongoing block layer requests submitted to the loop device to finish. All
> later submit_bio(), generic_make_request(), direct_make_request() and
> blk_get_request() calls will fail with BLK_STS_IOERR or -ENODEV, including
> those triggered by kill_bdev(). In other words, the above patch causes I/O
> to fail that is submitted concurrently with kill_bdev(). Do you agree with
> failing I/O requests submitted to a loop device while the loop device block
> size, offset and/or size are being modified?
Actually, the previous patch returned EAGAIN, if there was an interim IO which
produced some dirty pages betwen kill_bdev() and blk_mq_freeze_queue_wait().
IMHO, we can't do blk_set_queue_dying() which gives EIO to those IOs.
Looking at the flow again, how about this?
---
drivers/block/loop.c | 67 ++++++++++++++++++++++----------------------
fs/block_dev.c | 12 ++++++++
include/linux/fs.h | 3 ++
3 files changed, 48 insertions(+), 34 deletions(-)
diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index f6f77eaa7217..0f3eca774655 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -1224,6 +1224,23 @@ static int loop_clr_fd(struct loop_device *lo)
return __loop_clr_fd(lo, false);
}
+static void
+loop_mq_freeze_queue(struct loop_device *lo)
+{
+ for (;;) {
+ sync_blockdev(lo->lo_device);
+
+ /* I/O need to be drained during transfer transition */
+ blk_mq_freeze_queue(lo->lo_queue);
+
+ if (is_dirty_bdev(lo->lo_device))
+ blk_mq_unfreeze_queue(lo->lo_queue);
+ else
+ break;
+ }
+ kill_bdev(lo->lo_device);
+}
+
static int
loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
{
@@ -1232,6 +1249,7 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
kuid_t uid = current_uid();
struct block_device *bdev;
bool partscan = false;
+ bool drop_cache;
err = mutex_lock_killable(&loop_ctl_mutex);
if (err)
@@ -1251,14 +1269,14 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
goto out_unlock;
}
- if (lo->lo_offset != info->lo_offset ||
- lo->lo_sizelimit != info->lo_sizelimit) {
- sync_blockdev(lo->lo_device);
- kill_bdev(lo->lo_device);
- }
+ drop_cache = (lo->lo_offset != info->lo_offset ||
+ lo->lo_sizelimit != info->lo_sizelimit);
/* I/O need to be drained during transfer transition */
- blk_mq_freeze_queue(lo->lo_queue);
+ if (drop_cache)
+ loop_mq_freeze_queue(lo);
+ else
+ blk_mq_freeze_queue(lo->lo_queue);
err = loop_release_xfer(lo);
if (err)
@@ -1283,16 +1301,7 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
if (err)
goto out_unfreeze;
- if (lo->lo_offset != info->lo_offset ||
- lo->lo_sizelimit != info->lo_sizelimit) {
- /* kill_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;
- }
+ if (drop_cache) {
if (figure_loop_size(lo, info->lo_offset, info->lo_sizelimit)) {
err = -EFBIG;
goto out_unfreeze;
@@ -1518,7 +1527,7 @@ static int loop_set_dio(struct loop_device *lo, unsigned long arg)
static int loop_set_block_size(struct loop_device *lo, unsigned long arg)
{
- int err = 0;
+ bool drop_cache;
if (lo->lo_state != Lo_bound)
return -ENXIO;
@@ -1526,31 +1535,21 @@ static int loop_set_block_size(struct loop_device *lo, unsigned long arg)
if (arg < 512 || arg > PAGE_SIZE || !is_power_of_2(arg))
return -EINVAL;
- if (lo->lo_queue->limits.logical_block_size != arg) {
- sync_blockdev(lo->lo_device);
- kill_bdev(lo->lo_device);
- }
-
- blk_mq_freeze_queue(lo->lo_queue);
+ drop_cache = (lo->lo_queue->limits.logical_block_size != arg);
- /* kill_bdev should have truncated all the pages */
- if (lo->lo_queue->limits.logical_block_size != arg &&
- 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;
- }
+ /* I/O need to be drained during transfer transition */
+ if (drop_cache)
+ loop_mq_freeze_queue(lo);
+ else
+ blk_mq_freeze_queue(lo->lo_queue);
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);
- return err;
+ return 0;
}
static int lo_simple_ioctl(struct loop_device *lo, unsigned int cmd,
diff --git a/fs/block_dev.c b/fs/block_dev.c
index 9c073dbdc1b0..81fe3beef92b 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -74,6 +74,18 @@ static void bdev_write_inode(struct block_device *bdev)
spin_unlock(&inode->i_lock);
}
+bool is_dirty_bdev(struct block_device *bdev)
+{
+ struct inode *inode = bdev->bd_inode;
+ bool dirty;
+
+ spin_lock(&inode->i_lock);
+ dirty = inode->i_state & I_DIRTY ? true: false;
+ spin_unlock(&inode->i_lock);
+ return dirty;
+}
+EXPORT_SYMBOL(is_dirty_bdev);
+
/* Kill _all_ buffers and pagecache , dirty or not.. */
void kill_bdev(struct block_device *bdev)
{
diff --git a/include/linux/fs.h b/include/linux/fs.h
index e0d909d35763..02156ad96be2 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2570,6 +2570,7 @@ extern void bdput(struct block_device *);
extern void invalidate_bdev(struct block_device *);
extern void iterate_bdevs(void (*)(struct block_device *, void *), void *);
extern int sync_blockdev(struct block_device *bdev);
+extern bool is_dirty_bdev(struct block_device *bdev);
extern void kill_bdev(struct block_device *);
extern struct super_block *freeze_bdev(struct block_device *);
extern void emergency_thaw_all(void);
@@ -2583,9 +2584,11 @@ static inline bool sb_is_blkdev_sb(struct super_block *sb)
{
return sb == blockdev_superblock;
}
+
#else
static inline void bd_forget(struct inode *inode) {}
static inline int sync_blockdev(struct block_device *bdev) { return 0; }
+static inline bool is_dirty_bdev(struct block_device *bdev) { return false; }
static inline void kill_bdev(struct block_device *bdev) {}
static inline void invalidate_bdev(struct block_device *bdev) {}
--
2.19.0.605.g01d371f741-goog
