Re: [PATCHv10 4/9] block: allow ability to limit partition write hints

[Keith Busch <kbusch@kernel.org>]

On Wed, Oct 30, 2024 at 05:46:58AM +0100, Christoph Hellwig wrote:
> On Tue, Oct 29, 2024 at 10:25:11AM -0700, Bart Van Assche wrote:
> >> +}
> >
> > bitmap_copy() is not atomic. Shouldn't the bitmap_copy() call be
> > serialized against the code that tests bits in bdev->write_hint_mask?
> 
> It needs something.  I actually pointed that out last round, but forgot
> about it again this time :)

I disagree. Whether we serialize it or not, writes in flight will either
think it can write or it won't. There's no point adding any overhead to
the IO path for this as you can't stop ending up with inflight writes
using the tag you're trying to turn off.

This is the same as the "ro" attribute. If you're changing it with
BLKROSET ioctl with writes in flight, some of those writes may get past
blkdev_write_iter's read-only check, others may not. No serialization
done there, and this pretty much the same thing.