On Wed, Nov 25, 2015 at 10:37:24AM -0800, Dan Williams wrote:
> Set SB_I_BDIDEAD when a block device is no longer available to service
> requests. This will be used in several places where an fs should give
> up early because the block device is gone. Letting the fs continue on
> as if the block device is still present can lead to long latencies
> waiting for an fs to detect the loss of its backing device, trigger
> crashes, or generate misleasing warnings.
>
> Cc: Jan Kara <jack@xxxxxxxx>
> Cc: Jens Axboe <axboe@xxxxxx>
> Suggested-by: Dave Chinner <david@xxxxxxxxxxxxx>
This isn't what I suggested. :/
.....
> diff --git a/fs/block_dev.c b/fs/block_dev.c
> index 1dd416bf72f7..d0233d643d33 100644
> --- a/fs/block_dev.c
> +++ b/fs/block_dev.c
> @@ -1795,6 +1795,23 @@ int __invalidate_device(struct block_device *bdev, bool kill_dirty)
> }
> EXPORT_SYMBOL(__invalidate_device);
>
> +void kill_bdev_super(struct gendisk *disk, int partno)
> +{
> + struct block_device *bdev = bdget_disk(disk, partno);
> + struct super_block *sb;
> +
> + if (!bdev)
> + return;
> + sb = get_super(bdev);
> + if (!sb)
> + goto out;
> +
> + sb->s_iflags |= SB_I_BDI_DEAD;
> + drop_super(sb);
> + out:
> + bdput(bdev);
> +}
That's not a notification to the filesystem - that's a status flag
the filesystem has to explicitly check for *on every operation*. We
already have checks like these throughout filesystems, but they are
filesystem specific and need to propagate into fs-specific
subsystems that have knowledge of VFS level superblocks.
To that end, what I actually suggested what a callback - something
like a function in the super operations structure so that the
filesystem can take *immediate action* when the block device is
dying. i.e.
void kill_bdev_super(struct gendisk *disk, int partno)
{
struct block_device *bdev = bdget_disk(disk, partno);
struct super_block *sb;
if (!bdev)
return;
sb = get_super(bdev);
if (!sb)
goto out;
if (sb->s_ops->shutdown)
sb->s_ops->shutdown(sb);
drop_super(sb);
out:
bdput(bdev);
}
and then we implement ->shutdown somthing like this in XFS:
xfs_fs_shutdown(struct superblock *sb)
{
xfs_force_shutdown(XFS_M(sb), SHUTDOWN_DEVICE_REQ);
}
and so we immediately notify the entire filesystem that a shutdown
state has been entered and the appropriate actions are immediately
taken.
Cheers,
Dave.
--
Dave Chinner
david@xxxxxxxxxxxxx
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