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

[Paolo Bonzini <pbonzini@redhat.com>]

On 24/03/21 17:23, Stefan Hajnoczi wrote:
> 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.

Cool, none of them seem to be blockers but you raised good points.  I'll 
send v6 tomorrow.

Paolo