Pavel Kozlov f2953184bf ARC: atomics: Add compiler barrier to atomic operations... ... commit 42f51fb24f upstream. ... to avoid unwanted gcc optimizations SMP kernels fail to boot with commit 596ff4a09b ("cpumask: re-introduce constant-sized cpumask optimizations"). | | 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. Fix this by add a compiler barrier (memory clobber in inline asm). Apparently atomic ops used to have memory clobber implicitly via surrounding smp_mb(). However commit b64be68369 ("ARC: atomics: implement relaxed variants") removed the smp_mb() for the relaxed variants, but failed to add the explicit compiler barrier. Link: https://github.com/foss-for-synopsys-dwc-arc-processors/linux/issues/135 Cc: <stable@vger.kernel.org> # v6.3+ Fixes: b64be68369 ("ARC: atomics: implement relaxed variants") Signed-off-by: Pavel Kozlov <pavel.kozlov@synopsys.com> Signed-off-by: Vineet Gupta <vgupta@kernel.org> [vgupta: tweaked the changelog and added Fixes tag] Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>		2023-09-19 12:28:04 +02:00
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