Date: Mon, 7 Sep 2015 14:01:18 +0000 (UTC) From: Andrew Turner <andrew@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r287536 - head/sys/arm64/arm64 Message-ID: <201509071401.t87E1IgI065372@repo.freebsd.org>
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Author: andrew Date: Mon Sep 7 14:01:18 2015 New Revision: 287536 URL: https://svnweb.freebsd.org/changeset/base/287536 Log: Use load-acquire semantics while waiting for td_lock to be released. The store should have release semantics and will have due to the dsb above it so add a comment to explain this. [1] While here update the code to not reload the current thread, it's already in a register, we just need to not trash it. Suggested by: kib [1] Sponsored by: ABT Systems Ltd Modified: head/sys/arm64/arm64/swtch.S Modified: head/sys/arm64/arm64/swtch.S ============================================================================== --- head/sys/arm64/arm64/swtch.S Mon Sep 7 14:00:38 2015 (r287535) +++ head/sys/arm64/arm64/swtch.S Mon Sep 7 14:01:18 2015 (r287536) @@ -160,17 +160,18 @@ ENTRY(cpu_switch) dsb sy isb - /* Release the old thread */ + /* + * Release the old thread. This doesn't need to be a store-release + * as the above dsb instruction will provide release semantics. + */ str x2, [x0, #TD_LOCK] #if defined(SCHED_ULE) && defined(SMP) /* Read the value in blocked_lock */ ldr x0, =_C_LABEL(blocked_lock) - ldr x1, [x0] - /* Load curthread */ - ldr x2, [x18, #PC_CURTHREAD] + ldr x2, [x0] 1: - ldr x3, [x2, #TD_LOCK] - cmp x3, x1 + ldar x3, [x1, #TD_LOCK] + cmp x3, x2 b.eq 1b #endif
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