linux-kernel - Re: [PATCH] x86/asm: Use CC_SET/CC_OUT in percpu_cmpxchg16b

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Date:   Sun, 30 Dec 2018 12:07:13 +0100
From:   Uros Bizjak <ubizjak@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     Uros Bizjak <ubizjak@...il.com>, x86@...nel.org
Subject: Re: [PATCH] x86/asm: Use CC_SET/CC_OUT in percpu_cmpxchg16b_double

On 12/28/18, Uros Bizjak <ubizjak@...il.com> wrote:
> Use CC_SET(z)/CC_OUT(z) instead of explicit setz instruction.
> Using these two defines, the compiler that supports generation of
> condition code outputs from inline assembly flags generates one
> conditional jump instruction, e.g:

Unfortunatelly, the 0day kernel test robot reports:

[    1.569154] DEBUG_LOCKS_WARN_ON(unlikely(early_boot_irqs_disabled))
[    1.569287] WARNING: CPU: 0 PID: 0 at kernel/locking/lockdep.c:2803
lockdep_hardirqs_on+0xc5/0x19e

presumably due to unconditional interrupt enable in
this_cpu_cmpxchg16b_emu. I have to somehow disable X86_FATURE_CX16 and
thoroughly test the library path.

Uros.