Re: [PATCH v5 0/6] coroutine rwlock downgrade fix, minor VDI changes

[Stefan Hajnoczi <stefanha@gmail.com>]

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On Wed, Mar 17, 2021 at 07:00:07PM +0100, Paolo Bonzini wrote:
> This is a resubmit of David Edmondson's series at
> https://patchew.org/QEMU/20210309144015.557477-1-david.edmondson@oracle.com/.
> After closer analysis on IRC, the CoRwlock's attempt to ensure
> fairness turned out to be flawed.  Therefore, this series
> reimplements CoRwlock without using a CoQueue.  Tracking whether
> each queued coroutine is a reader/writer makes it possible to
> never wake a writer when only readers should be allowed and
> vice versa.
> 
> v2->v3: new CoRwlock implementation
> 
> v3->v4: fix upgrade and add a test for that, too
> 
> v4->v5: typo
> 
> David Edmondson (4):
>   block/vdi: When writing new bmap entry fails, don't leak the buffer
>   block/vdi: Don't assume that blocks are larger than VdiHeader
>   coroutine/mutex: Store the coroutine in the CoWaitRecord only once
>   test-coroutine: Add rwlock downgrade test
> 
> Paolo Bonzini (2):
>   coroutine-lock: reimplement CoRwlock to fix downgrade bug
>   test-coroutine: add rwlock upgrade test
> 
>  block/vdi.c                 |  11 ++-
>  include/qemu/coroutine.h    |  17 ++--
>  tests/unit/test-coroutine.c | 161 ++++++++++++++++++++++++++++++++++++
>  util/qemu-coroutine-lock.c  | 149 +++++++++++++++++++++------------
>  4 files changed, 274 insertions(+), 64 deletions(-)

I had questions about the rwlock implementation. The other patches look
ready to go.

Stefan

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