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>
0476f2016d