time: switch to fences for siginfo_recvd
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Authored by kevans on Jun 13 2024, 5:29 AM.

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rGdf1b0f580d3d: time: switch to fences for siginfo_recvd

Summary

This effectively reverts
6e824f3713011 ("time: siginfo_recvd needs to be marked volatile")
because it was actually wrong. Switch to C11 signal fence, which
provides a compiler barrier that will do the right thing.

Reported by: kib

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rG FreeBSD src repository

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Event Timeline

kevans created this revision.Jun 13 2024, 5:29 AM

Herald added a subscriber: imp. · View Herald TranscriptJun 13 2024, 5:29 AM

kevans requested review of this revision.Jun 13 2024, 5:29 AM

Harbormaster completed remote builds in B58159: Diff 139798.Jun 13 2024, 5:29 AM

kib added inline comments.Jun 13 2024, 6:02 PM

usr.bin/time/time.c
130–133	I think that the right code is local_siginfo_recvd = siginfo_recvd; atomic_signal_fence(acq); if (local siginfo_recvd) { .... [Fence should come after reading the flag variable]