On 11/25/19 11:41 AM, Bart Van Assche wrote:
On 11/25/19 11:22 AM, Jaegeuk Kim wrote:
On 11/25, Bart Van Assche wrote:
Thank you for the additional and very helpful clarification. Can you
have a look at the (totally untested) patch below? I prefer that
version because it prevents concurrent processing of requests and
syncing/killing the bdev.
Yeah, I thought this was much cleaner way, but wasn't sure it could be
doable
to sync|kill block device after freezing the queue. Is it okay?
Hi Jaegeuk,
That patch was based on an incorrect interpretation of the meaning of
lo_device. After having taken another loop at the block driver, I don't
think that calling sync after freezing the queue is OK. How about using
the following call sequence:
* sync_blockdev()
* blk_mq_freeze_queue()
* kill_bdev()
This is what I had in mind (still untested):
Subject: [PATCH] loop: Avoid EAGAIN if the offset or the block_size are changed
After sync_blockdev() has been called, more requests can be submitted
to the loop device. These requests dirty additional pages, causing
loop_set_status() to return -EAGAIN. Not all user space code that
changes the offset and/or the block size handles -EAGAIN correctly.
Hence make sure that loop_set_status() does not return -EAGAIN.
Cc: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
Cc: Gwendal Grignou <gwendal@xxxxxxxxxxxx>
Cc: grygorii tertychnyi <gtertych@xxxxxxxxx>
Cc: Andrew Norrie <andrew.norrie@xxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Fixes: 5db470e229e2 ("loop: drop caches if offset or block_size are changed")
Reported-by: Gwendal Grignou <gwendal@xxxxxxxxxxxx>
Reported-by: grygorii tertychnyi <gtertych@xxxxxxxxx>
Reported-by: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
Signed-off-by: Bart Van Assche <bvanassche@xxxxxxx>
---
drivers/block/loop.c | 56 ++++++++++++++++++--------------------------
1 file changed, 23 insertions(+), 33 deletions(-)
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. */
+ kill_bdev(lo->lo_device);
err = loop_release_xfer(lo);
if (err)
@@ -1298,14 +1301,6 @@ 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) {
- /* 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 (figure_loop_size(lo, info->lo_offset, info->lo_sizelimit)) {
err = -EFBIG;
goto out_unfreeze;
@@ -1341,6 +1336,7 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
__loop_update_dio(lo, lo->use_dio);
out_unfreeze:
+ blk_queue_flag_clear(QUEUE_FLAG_DYING, lo->lo_queue);
blk_mq_unfreeze_queue(lo->lo_queue);
if (!err && (info->lo_flags & LO_FLAGS_PARTSCAN) &&
@@ -1531,39 +1527,33 @@ 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;
-
if (lo->lo_state != Lo_bound)
return -ENXIO;
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);
- }
+ /*
+ * Drain the page cache and the request queue. Set the "dying" flag to
+ * prevent that kill_bdev() locks up.
+ */
+ sync_blockdev(lo->lo_device);
- blk_mq_freeze_queue(lo->lo_queue);
+ blk_set_queue_dying(lo->lo_queue);
+ blk_mq_freeze_queue_wait(lo->lo_queue);
- /* 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;
- }
+ /* Kill buffers that got dirtied after the sync_blockdev() call. */
+ kill_bdev(lo->lo_device);
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_queue_flag_clear(QUEUE_FLAG_DYING, lo->lo_queue);
blk_mq_unfreeze_queue(lo->lo_queue);
- return err;
+ return 0;
}
static int lo_simple_ioctl(struct loop_device *lo, unsigned int cmd,
