Re: [PATCH 6/6] Call flush_disk() after detecting an online resize.

[Jeff Moyer <jmoyer@redhat.com>]

Andrew Patterson <andrew.patterson@hp.com> writes:

> Call flush_disk() after detecting an online resize.
>
> We call flush_disk() to make sure the buffer cache for the disk is
> flushed after a disk resize. There are two resize cases, growing and
> shrinking. Given that users can shrink/then grow a disk before
> revalidate_disk() is called, we treat the grow case identically to
> shrinking. We need to flush the buffer cache after an online shrink
> because, as James Bottomley puts it,
>
>      The two use cases for shrinking I can see are
>
>      1. planned: the fs is already shrunk to within the new boundaries
>         and all data is relocated, so invalidate is fine (any dirty
>         buffers that might exist in the shrunk region are there only
>         because they were relocated but not yet written to their
>         original location).
>      2. unplanned:  In this case, the fs is probably toast, so whether
>         we invalidate or not isn't going to make a whole lot of
>         difference; it's still going to try to read or write from
>         sectors beyond the new size and get I/O errors.
>
> Immediately invalidating shrunk disks will cause errors for outstanding
> I/Os for reads/write beyond the new end of the disk to be generated
> earlier then if we waited for the normal buffer cache operation. It also
> removes a potential security hole where we might keep old data around
> from beyond the end of the shrunk disk if the disk was not invalidated.
>
> Signed-off-by: Andrew Patterson <andrew.patterson@hp.com>
Reviewed-by: Jeff Moyer <jmoyer@redhat.com>