| commit | 17b2fb1b656a275906b5071c562439d50a27f167 | [log] [tgz] |
|---|---|---|
| author | Russ Cox <rsc@golang.org> | Wed Jan 12 17:22:09 2022 -0500 |
| committer | Russ Cox <rsc@golang.org> | Fri Jan 14 17:49:58 2022 +0000 |
| tree | f60646e797dbed14f7b8085c44c50ff4543f9c75 | |
| parent | b41185c5c3da2d5f52b3b5aa7eb034addd458938 [diff] |
runtime: fix net poll races 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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