Re: [PATCH] rqspinlock: Fix order in raw_res_spin_(un)lock_irq to allow schedule

[Arnd Bergmann]

On Tue, Jun 9, 2026, at 11:49, Gabriele Monaco wrote:
> raw_res_spin_unlock_irqrestore() calls raw_res_spin_unlock() and then
> restores interrupts, this means preemption is enabled when interrupts
> are still disabled (as part of raw_res_spin_unlock()) so this cannot
> trigger an actual preemption.
> This is inconsistent with other spinlock implementations
> (raw_spin_unlock_irqrestore() and bpf_res_spin_unlock_irqrestore()
> itself).
>
> Adjust the macro to ensure interrupts are enabled before enabling
> preemption, allowing to schedule at that point. Make the same
> modification in the error path of raw_res_spin_lock_irqsave().
>
> Fixes: 101acd2e78b1 ("rqspinlock: Add macros for rqspinlock usage")

Should this be Cc:stable@xxxxxxxxxxxxxxx to get backported?

Did you see this cause measurable performance problems,
or did you find it through inspection?

> Signed-off-by: Gabriele Monaco <gmonaco@xxxxxxxxxx>

Acked-by: Arnd Bergmann <arnd@xxxxxxxx> # asm-generic

This should probably get merged through the BPF tree, but I've
added the kernel/locking maintainers to Cc as well, since I
feel it's more useful to have them look at it than me.

Maybe it would be good to update (as a separate patch) the
MAINTAINERS file so the locking subsystem also includes the
headers currently missing:

arch/*/include/asm/*spinlock*.h
arch/*/include/asm/*rwlock*.h
include/asm-generic/*spinlock*.h
include/asm-generic/*rwlock*.h

       Arnd

(full patch quoted below)

> ---
>  include/asm-generic/rqspinlock.h | 14 +++++++++++---
>  1 file changed, 11 insertions(+), 3 deletions(-)
>
> diff --git a/include/asm-generic/rqspinlock.h 
> b/include/asm-generic/rqspinlock.h
> index 151d267a49..4d46643f46 100644
> --- a/include/asm-generic/rqspinlock.h
> +++ b/include/asm-generic/rqspinlock.h
> @@ -243,12 +243,20 @@ static __always_inline void 
> res_spin_unlock(rqspinlock_t *lock)
>  	({                                        \
>  		int __ret;                        \
>  		local_irq_save(flags);            \
> -		__ret = raw_res_spin_lock(lock);  \
> -		if (__ret)                        \
> +		preempt_disable();                \
> +		__ret = res_spin_lock(lock);      \
> +		if (__ret) {                      \
>  			local_irq_restore(flags); \
> +			preempt_enable();         \
> +		}                                 \
>  		__ret;                            \
>  	})
> 
> -#define raw_res_spin_unlock_irqrestore(lock, flags) ({ 
> raw_res_spin_unlock(lock); local_irq_restore(flags); })
> +#define raw_res_spin_unlock_irqrestore(lock, flags) \
> +	({                                          \
> +		res_spin_unlock(lock);              \
> +		local_irq_restore(flags);           \
> +		preempt_enable();                   \
> +	})
> 
>  #endif /* __ASM_GENERIC_RQSPINLOCK_H */
>
> base-commit: e43ffb69e0438cddd72aaa30898b4dc446f664f8
> -- 
> 2.54.0