Hi, On 2025-06-12 15:12:00 +0300, Konstantin Knizhnik wrote: > Reproduced it once again with with write-protected io handle. > But once again - no access violation, just assert failure. > > Previously "op" field was overwritten somewhere between `pgaio_io_reclaim` > and `AsyncReadBuffers`: > > !!!pgaio_io_reclaim [20376]| ioh: 0x1019bc000, ioh->op: 0, ioh->generation: > 19346 > !!!AsyncReadBuffers [20376] (1)| blocknum: 21, ioh: 0x1019bc000, ioh->op: 1, > ioh->state: 1, ioh->result: 0, ioh->num_callbacks: 0, ioh->generation: 19346 > > Now it is overwritten after print in AsyncReadBuffers: > > !!!pgaio_io_reclaim [88932]| ioh: 0x105a5c000, ioh->op: 0, ioh->generation: > 42848 > !!!pgaio_io_acquire_nb[88932]| ioh: 0x105a5c000, ioh->op: 0, > ioh->generation: 42848 > !!!AsyncReadBuffers [88932] (1)| blocknum: 10, ioh: 0x105a5c000, ioh->op: 0, > ioh->state: 1, ioh->result: 0, ioh->num_callbacks: 0, ioh->generation: 42848 > !!!pgaio_io_before_start| ioh: 0x105a5c000, ioh->op: 1, ioh->state: 1, > ioh->result: 0, ioh->num_callbacks: 2, ioh->generation: 42848 > > In this run I prohibit writes to io handle in `pgaio_io_acquire_nb` and > reenable them in `AsyncReadBuffer`.
I'm reasonably certain I found the issue, I think it's a missing memory barrier on the read side. The CPU is reordering the read (or just using a cached value) of ->distilled_result to be before the load of ->state. But it'll take a bit to verify that that's the issue... Greetings, Andres Freund
