17b2fb1b65
The netpoll code was written long ago, when the only multiprocessors that Go ran on were x86. It assumed that an atomic store would trigger a full memory barrier and then used that barrier to order otherwise racy access to a handful of fields, including pollDesc.closing. On ARM64, this code has finally failed, because the atomic store is on a value completely unrelated to any of the racily-accessed fields, and the ARMv8 hardware, unlike x86, is clever enough not to do a full memory barrier for a simple atomic store. We are seeing a constant background rate of trybot failures where the net/http tests deadlock - a netpollblock has clearly happened after the pollDesc has begun to close. The code that does the racy reads is netpollcheckerr, which needs to be able to run without acquiring a lock. This CL fixes the race, without introducing unnecessary inefficiency or deadlock, by arranging for every updater of the relevant fields to publish a summary as a single atomic uint32, and then having netpollcheckerr use a single atomic load to fetch the relevant bits and then proceed as before. Fixes #45211 (until proven otherwise!). Change-Id: Ib6788c8da4d00b7bda84d55ca3fdffb5a64c1a0a Reviewed-on: https://go-review.googlesource.com/c/go/+/378234 Trust: Russ Cox <rsc@golang.org> Run-TryBot: Russ Cox <rsc@golang.org> Trust: Bryan Mills <bcmills@google.com> Reviewed-by: Ian Lance Taylor <iant@golang.org> |
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