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Message-ID: <CAADnVQLz=+FN8-B_QmmT-eg7PB7jGHiah=9B-s5WpfmQbAF3eg@mail.gmail.com>
Date: Wed, 14 May 2025 17:46:43 -0700
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc: LKML <linux-kernel@...r.kernel.org>, linux-rt-devel@...ts.linux.dev,
Thomas Gleixner <tglx@...utronix.de>, Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>, Waiman Long <longman@...hat.com>,
Boqun Feng <boqun.feng@...il.com>
Subject: Re: [PATCH 1/2] local_lock: Move this_cpu_ptr() notation from
internal to main header.
On Wed, May 14, 2025 at 4:07 AM Sebastian Andrzej Siewior
<bigeasy@...utronix.de> wrote:
>
> The local_lock.h is the main entry for the local_lock_t type and
> provides wrappers around internal functions prefixed with __ in
> local_lock_internal.h.
>
> Move the this_cpu_ptr() dereference of the variable from the internal to
> the main header. Since it is all macro implemented, this_cpu_ptr() will
> still happen within the preempt/ IRQ disabled section.
> This will free the internal implementation (__) to be used on
> local_lock_t types which are local variables and must not be accessed
> via this_cpu_ptr().
>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> ---
> include/linux/local_lock.h | 20 +++++++++----------
> include/linux/local_lock_internal.h | 30 ++++++++++++++---------------
> 2 files changed, 25 insertions(+), 25 deletions(-)
>
> diff --git a/include/linux/local_lock.h b/include/linux/local_lock.h
> index 16a2ee4f8310b..2ba8464195244 100644
> --- a/include/linux/local_lock.h
> +++ b/include/linux/local_lock.h
> @@ -13,13 +13,13 @@
> * local_lock - Acquire a per CPU local lock
> * @lock: The lock variable
> */
> -#define local_lock(lock) __local_lock(lock)
> +#define local_lock(lock) __local_lock(this_cpu_ptr(lock))
>
> /**
> * local_lock_irq - Acquire a per CPU local lock and disable interrupts
> * @lock: The lock variable
> */
> -#define local_lock_irq(lock) __local_lock_irq(lock)
> +#define local_lock_irq(lock) __local_lock_irq(this_cpu_ptr(lock))
>
> /**
> * local_lock_irqsave - Acquire a per CPU local lock, save and disable
> @@ -28,19 +28,19 @@
> * @flags: Storage for interrupt flags
> */
> #define local_lock_irqsave(lock, flags) \
> - __local_lock_irqsave(lock, flags)
> + __local_lock_irqsave(this_cpu_ptr(lock), flags)
>
> /**
> * local_unlock - Release a per CPU local lock
> * @lock: The lock variable
> */
> -#define local_unlock(lock) __local_unlock(lock)
> +#define local_unlock(lock) __local_unlock(this_cpu_ptr(lock))
>
> /**
> * local_unlock_irq - Release a per CPU local lock and enable interrupts
> * @lock: The lock variable
> */
> -#define local_unlock_irq(lock) __local_unlock_irq(lock)
> +#define local_unlock_irq(lock) __local_unlock_irq(this_cpu_ptr(lock))
>
> /**
> * local_unlock_irqrestore - Release a per CPU local lock and restore
> @@ -49,7 +49,7 @@
> * @flags: Interrupt flags to restore
> */
> #define local_unlock_irqrestore(lock, flags) \
> - __local_unlock_irqrestore(lock, flags)
> + __local_unlock_irqrestore(this_cpu_ptr(lock), flags)
>
> /**
> * local_lock_init - Runtime initialize a lock instance
> @@ -64,7 +64,7 @@
> * locking constrains it will _always_ fail to acquire the lock in NMI or
> * HARDIRQ context on PREEMPT_RT.
> */
> -#define local_trylock(lock) __local_trylock(lock)
> +#define local_trylock(lock) __local_trylock(this_cpu_ptr(lock))
>
> /**
> * local_trylock_irqsave - Try to acquire a per CPU local lock, save and disable
> @@ -77,7 +77,7 @@
> * HARDIRQ context on PREEMPT_RT.
> */
> #define local_trylock_irqsave(lock, flags) \
> - __local_trylock_irqsave(lock, flags)
> + __local_trylock_irqsave(this_cpu_ptr(lock), flags)
>
> DEFINE_GUARD(local_lock, local_lock_t __percpu*,
> local_lock(_T),
> @@ -91,10 +91,10 @@ DEFINE_LOCK_GUARD_1(local_lock_irqsave, local_lock_t __percpu,
> unsigned long flags)
>
> #define local_lock_nested_bh(_lock) \
> - __local_lock_nested_bh(_lock)
> + __local_lock_nested_bh(this_cpu_ptr(_lock))
>
> #define local_unlock_nested_bh(_lock) \
> - __local_unlock_nested_bh(_lock)
> + __local_unlock_nested_bh(this_cpu_ptr(_lock))
>
> DEFINE_GUARD(local_lock_nested_bh, local_lock_t __percpu*,
> local_lock_nested_bh(_T),
> diff --git a/include/linux/local_lock_internal.h b/include/linux/local_lock_internal.h
> index 8d5ac16a9b179..b4d7b24882835 100644
> --- a/include/linux/local_lock_internal.h
> +++ b/include/linux/local_lock_internal.h
> @@ -99,14 +99,14 @@ do { \
> local_trylock_t *tl; \
> local_lock_t *l; \
> \
> - l = (local_lock_t *)this_cpu_ptr(lock); \
> + l = (local_lock_t *)(lock); \
> tl = (local_trylock_t *)l; \
> _Generic((lock), \
> - __percpu local_trylock_t *: ({ \
> + local_trylock_t *: ({ \
> lockdep_assert(tl->acquired == 0); \
> WRITE_ONCE(tl->acquired, 1); \
> }), \
> - __percpu local_lock_t *: (void)0); \
> + local_lock_t *: (void)0); \
Are you sure this is correct?
Have you tested with gcc 14 or higher?
It looks to me that moving this_cpu_ptr() up one level should
still preserve __seg_gs modifier.
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