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net,runtime: apparent deadlock in (*net.conn).Close and runtime.netpollblock on arm64 platforms [1.16 backport] #49009

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gopherbot opened this issue Oct 15, 2021 · 3 comments
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net,runtime: apparent deadlock in (*net.conn).Close and runtime.netpollblock on arm64 platforms [1.16 backport] #49009

gopherbot opened this issue Oct 15, 2021 · 3 comments
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CherryPickApproved Used during the release process for point releases FrozenDueToAge
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Go1.16.10

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@gopherbot
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@prattmic requested issue #48925 to be considered for backport to the next 1.16 minor release.

@LaPingvino give the new version a try, though it sounds like you may be having a different issue. Logs would definitely help.

@gopherbot please backport to 1.17 and 1.16. This is a pre-existing issue with no workaround, and causing flakes on trybots.
@gopherbot gopherbot added the CherryPickCandidate Used during the release process for point releases label Oct 15, 2021
@gopherbot gopherbot mentioned this issue Oct 15, 2021
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@gopherbot gopherbot added this to the Go1.16.10 milestone Oct 15, 2021
@gopherbot
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Change https://golang.org/cl/356370 mentions this issue: [release-branch.go1.16] runtime: consistently access pollDesc r/w Gs with atomics

@cherrymui
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This is serious runtime issue. Approved for backport. Thanks.

@cherrymui cherrymui added CherryPickApproved Used during the release process for point releases and removed CherryPickCandidate Used during the release process for point releases labels Oct 20, 2021
@gopherbot
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Closed by merging 8c9c148 to release-branch.go1.16.

gopherbot pushed a commit that referenced this issue Oct 28, 2021
@prattmic @dmitshur
[release-branch.go1.16] runtime: consistently access pollDesc r/w Gs …
8c9c148 
…with atomics

Both netpollblock and netpollunblock read gpp using a non-atomic load.
When consuming a ready event, netpollblock clears gpp using a non-atomic
store, thus skipping a barrier.

Thus on systems with weak memory ordering, a sequence like so this is
possible:

             T1                                T2

1. netpollblock: read gpp -> pdReady
2. netpollblock: store gpp -> 0

                                 3. netpollunblock: read gpp -> pdReady
                                 4. netpollunblock: return

i.e., without a happens-before edge between (2) and (3), netpollunblock
may read the stale value of gpp.

Switch these access to use atomic loads and stores in order to create
these edges.

For ease of future maintainance, I've simply changed rg and wg to always
be accessed atomically, though I don't believe pollOpen or pollClose
require atomics today.

For #48925
Fixes #49009

Change-Id: I903ea667eea320277610b4f969129935731520c3
Reviewed-on: https://go-review.googlesource.com/c/go/+/355952
Trust: Michael Pratt <[email protected]>
Run-TryBot: Michael Pratt <[email protected]>
TryBot-Result: Go Bot <[email protected]>
Reviewed-by: Michael Knyszek <[email protected]>
Reviewed-by: David Chase <[email protected]>
(cherry picked from commit 1b072b3)
Reviewed-on: https://go-review.googlesource.com/c/go/+/356370
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