Hi Bart, On 11/25, Bart Van Assche wrote: > On 11/25/19 9:59 AM, Jaegeuk Kim wrote: > > On 11/19, Bart Van Assche wrote: > > > On 5/17/19 5:53 PM, Jaegeuk Kim wrote: > > > > This patch tries to avoid EAGAIN due to nrpages!=0 that was originally trying > > > > to drop stale pages resulting in wrong data access. > > > > > > > > Report: https://bugs.chromium.org/p/chromium/issues/detail?id=938958#c38 > > > > > > Please provide a more detailed commit description. What is wrong with the > > > current implementation and why is the new behavior considered the correct > > > behavior? > > > > Some history would be: > > > > Original bug fix is: > > commit 5db470e229e2 ("loop: drop caches if offset or block_size are changed"), > > which returns EAGAIN so that user land like Chrome would require enhancing their > > error handling routines. > > > > So, this patch tries to avoid EAGAIN while addressing the original bug. > > > > > > > > This patch moves draining code from before the following comment to after > > > that comment: > > > > > > /* I/O need to be drained during transfer transition */ > > > > > > Is that comment still correct or should it perhaps be updated? > > > > IMHO, it's still valid. > > Hi Jaegeuk, > > 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? > > Thanks, > > Bart. > > > Subject: [PATCH] loop: Avoid EAGAIN if offset or block_size are changed > > After sync_blockdev() and kill_bdev() have 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. > > 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> > Cc: <stable@xxxxxxxxxxxxxxx> > Signed-off-by: Bart Van Assche <bvanassche@xxxxxxx> > --- > drivers/block/loop.c | 35 +++++++---------------------------- > 1 file changed, 7 insertions(+), 28 deletions(-) > > diff --git a/drivers/block/loop.c b/drivers/block/loop.c > index 739b372a5112..48cfc8b9c247 100644 > --- a/drivers/block/loop.c > +++ b/drivers/block/loop.c > @@ -1264,15 +1264,15 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info) > goto out_unlock; > } > > + /* I/O need to be drained during transfer transition */ > + blk_mq_freeze_queue(lo->lo_queue); > + > if (lo->lo_offset != info->lo_offset || > lo->lo_sizelimit != info->lo_sizelimit) { > sync_blockdev(lo->lo_device); > kill_bdev(lo->lo_device); > } > > - /* I/O need to be drained during transfer transition */ > - blk_mq_freeze_queue(lo->lo_queue); > - > err = loop_release_xfer(lo); > if (err) > goto out_unfreeze; > @@ -1298,14 +1298,6 @@ 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; > @@ -1531,39 +1523,26 @@ 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; > > + blk_mq_freeze_queue(lo->lo_queue); > + > 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); > - > - /* 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; > - } > - > 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,
