[<prev] [next>] [<thread-prev] [day] [month] [year] [list]
Message-ID: <ed79681e-ecd1-3129-5ad1-2965e2cd42b5@kernel.org>
Date: Tue, 15 Aug 2023 09:12:48 -0700
From: Vineet Gupta <vgupta@...nel.org>
To: Pavel.Kozlov@...opsys.com, linux-snps-arc@...ts.infradead.org
Cc: linux-kernel@...r.kernel.org, vgupta@...nel.org,
stable@...r.kernel.org
Subject: Re: [PATCH] ARC: avoid unwanted gcc optimizations in atomic
operations
On 8/15/23 08:11, Pavel.Kozlov@...opsys.com wrote:
> From: Pavel Kozlov<pavel.kozlov@...opsys.com>
>
> Notify a compiler about write operations and prevent unwanted
> optimizations. Add the "memory" clobber to the clobber list.
>
> An obvious problem with unwanted compiler optimizations appeared after
> the cpumask optimization commit 596ff4a09b89 ("cpumask: re-introduce
> constant-sized cpumask optimizations").
>
> After this commit the SMP kernels for ARC no longer loads because of
> failed assert in the percpu allocator initialization routine:
>
> percpu: BUG: failure at mm/percpu.c:2981/pcpu_build_alloc_info()!
>
> The write operation performed by the scond instruction in the atomic
> inline asm code is not properly passed to the compiler. The compiler
> cannot correctly optimize a nested loop that runs through the cpumask
> in the pcpu_build_alloc_info() function.
>
> Add the "memory" clobber to fix this.
>
> Link:https://github.com/foss-for-synopsys-dwc-arc-processors/linux/issues/135
> Cc:<stable@...r.kernel.org> # v6.3+
> Signed-off-by: Pavel Kozlov<pavel.kozlov@...opsys.com>
Acked-by: Vineet Gupta <vgupta@...nel.org>
Fixes: b64be6836993c431e ("ARC: atomics: implement relaxed variants")
Before that commit, atomic ops could elide memory clobber because the
trailing smp_mb() did that anyways.
However after that commit, the smp_mb() was optional for relaxed
variants and thus needs clobber.
Powered by blists - more mailing lists