Re: [PATCH] memory/ramblock: Fix clear of mru_block on possible race condition

[Peter Xu <peterx@redhat.com>]

On Thu, Jun 04, 2026 at 02:24:07PM +0900, Akihiko Odaki wrote:
> On 2026/06/04 2:35, Peter Xu wrote:
> > On Wed, Jun 03, 2026 at 02:11:44PM +0900, Akihiko Odaki wrote:
> > > qemu_get_ram_block() may set mru_block during the grace period. Once
> > > mru_block is set, RCU readers can still access the ramblock, even if the
> > > block is no longer visible in ram_list.
> > 
> > True..
> > 
> > > 
> > > When enriching the comment in reclaim_ramblock_prepare(), I think the phrase
> > > “the last reader that can access this ramblock is gone” could be improved.
> > > What matters here is that the last reader that could find the block in
> > > ram_list is gone. The block is no longer visible in ram_list to any later
> > > reader, and clearing the cache at that point ensures that it is no longer
> > > visible through an mru_block cache hit either.
> > 
> > Yes that's ambiguous.
> > 
> > I updated comments in this patch, removed the 1st reset of mru_block, and
> > when at it also touched up the comment in qemu_get_ram_block(), let me know
> > if there's further comments before repost.
> 
> It looks good. You may repost it with my Reviewed-by added:
> 
> Reviewed-by: Akihiko Odaki <odaki@rsg.ci.i.u-tokyo.ac.jp>

Thanks.

-- 
Peter Xu