Hi Stefan, On Wed, Jun 1, 2022 at 6:56 AM Stefan Hajnoczi <stefa...@gmail.com> wrote: > > > > This patch makes sense to me. Can you rephrase your concern? > > > > The locking is around dbs->io_func(). > > > > aio_context_acquire(dbs->ctx); > > dbs->acb = dbs->io_func() > > aio_context_release(dbs->ctx); > > > > > > So where exactly would the lock that's now still held stop someone from > > modifying dbs->acb = NULL at the beginning of the function, which seems > > to be not protected by that lock? > > > > Maybe I'm missing some locking magic due to the lock being a recursive lock. > > Tong Zhang: Can you share a backtrace of all threads when the > assertion failure occurs? > Sorry I couldn't get the trace now -- but I can tell that we have some internal code uses this dma related code and will grab dbs->ctx lock in another thread and could overwrite dbs->acb.
>From my understanding, one of the reasons that the lock is required here is to protect dbs->acb, we could not reliably test io_func()'s return value after releasing the lock here. Since this code affects our internal code base and I did not reproduce on master branch, feel free to ignore it. - Tong > Stefan
