Re: [PATCH v9 04/12] arm64: support WFET in smp_cond_load_relaxed_timeout()
From: Ankur Arora <hidden>
Date: 2026-02-11 23:14:08
Also in:
bpf, linux-arch, linux-pm, lkml
Catalin Marinas [off-list ref] writes:
On Sun, Feb 08, 2026 at 06:31:45PM -0800, Ankur Arora wrote:quoted
diff --git a/arch/arm64/include/asm/cmpxchg.h b/arch/arm64/include/asm/cmpxchg.h index d7a540736741..dfb7d10a18be 100644 --- a/arch/arm64/include/asm/cmpxchg.h +++ b/arch/arm64/include/asm/cmpxchg.h@@ -12,6 +12,7 @@ #include <asm/barrier.h> #include <asm/lse.h> +#include <asm/delay-const.h> /* * We need separate acquire parameters for ll/sc and lse, since the full@@ -208,9 +209,13 @@ __CMPXCHG_GEN(_mb) __cmpxchg128((ptr), (o), (n)); \ }) +/* Re-declared here to avoid include dependency. */ +extern u64 (*arch_timer_read_counter)(void);We have a bug in udelay() because the above might read the physical counter while WFET uses the virtual one. See this thread: https://lore.kernel.org/all/ktosachvft2cgqd5qkukn275ugmhy6xrhxur4zqpdxlfr3qh5h@o3zrfnsq63od/ (local)
Oh that looks painful. Thanks for linking it.
We could use __arch_counter_get_cntvct_stable() as in Marc's suggestion for the udelay() fix (or just wait to see the outcome of the above thread).
Yeah will follow where that goes.
The rest looks fine.
Great. Thanks! -- ankur