On Tue, Nov 07, 2017 at 04:09:37PM +0100, Sergio Lopez wrote: > Commit b7a745d added a qemu_bh_cancel call to the completion function > as an optimization to prevent it from unnecessarily rescheduling itself. > > This completion function is scheduled from worker_thread, after setting > the state of a ThreadPoolElement to THREAD_DONE. > > This was considered to be safe, as the completion function restarts the > loop just after the call to qemu_bh_cancel. But, under certain access > patterns and scheduling conditions, the loop may wrongly use a > pre-fetched elem->state value, reading it as THREAD_QUEUED, and ending > the completion function without having processed a pending TPE linked at > pool->head. > > In some situations, if there are no other independent requests in the > same aio context that could eventually trigger the scheduling of the > completion function, the omitted TPE and all operations pending on it > will get stuck forever. > > Signed-off-by: Sergio Lopez <s...@redhat.com> > --- > util/async.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-)
Reviewed-by: Stefan Hajnoczi <stefa...@redhat.com>
signature.asc
Description: PGP signature
