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From: Peter Zijlstra <peterz@infradead.org>
To: "André Almeida" <andrealmeid@collabora.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>,
	Darren Hart <dvhart@infradead.org>,
	linux-kernel@vger.kernel.org,
	Steven Rostedt <rostedt@goodmis.org>,
	Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
	kernel@collabora.com, krisman@collabora.com,
	pgriffais@valvesoftware.com, z.figura12@gmail.com,
	joel@joelfernandes.org, malteskarupke@fastmail.fm,
	linux-api@vger.kernel.org, fweimer@redhat.com,
	libc-alpha@sourceware.org, linux-kselftest@vger.kernel.org,
	shuah@kernel.org, acme@kernel.org, corbet@lwn.net
Subject: Re: [RFC PATCH 01/13] futex2: Implement wait and wake functions
Date: Tue, 16 Feb 2021 10:35:02 +0100	[thread overview]
Message-ID: <YCuRxl4uRhua+Y5b@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20210215152404.250281-2-andrealmeid@collabora.com>

On Mon, Feb 15, 2021 at 12:23:52PM -0300, André Almeida wrote:

> +static int futex_dequeue_multiple(struct futexv_head *futexv, unsigned int nr)
> +{
> +	int i, ret = -1;
> +
> +	for (i = 0; i < nr; i++) {
> +		spin_lock(&futexv->objects[i].bucket->lock);
> +		if (!list_empty_careful(&futexv->objects[i].list)) {
> +			list_del_init_careful(&futexv->objects[i].list);
> +			bucket_dec_waiters(futexv->objects[i].bucket);

What's with the careful? AFAICT all sites have that bucket->lock.

> +		} else {
> +			ret = i;
> +		}
> +		spin_unlock(&futexv->objects[i].bucket->lock);
> +	}
> +
> +	return ret;
> +}

> +static int futex_enqueue(struct futexv_head *futexv, unsigned int nr_futexes,
> +			 int *awakened)
> +{
> +	int i, ret;
> +	u32 uval, *uaddr, val;
> +	struct futex_bucket *bucket;
> +
> +retry:
> +	set_current_state(TASK_INTERRUPTIBLE);
> +
> +	for (i = 0; i < nr_futexes; i++) {
> +		uaddr = (u32 * __user)futexv->objects[i].uaddr;
> +		val = (u32)futexv->objects[i].val;
> +
> +		bucket = futexv->objects[i].bucket;
> +
> +		bucket_inc_waiters(bucket);
> +		spin_lock(&bucket->lock);
> +
> +		ret = futex_get_user(&uval, uaddr);
> +
> +		if (unlikely(ret)) {
> +			spin_unlock(&bucket->lock);
> +
> +			bucket_dec_waiters(bucket);
> +			__set_current_state(TASK_RUNNING);
> +			*awakened = futex_dequeue_multiple(futexv, i);
> +
> +			if (__get_user(uval, uaddr))
> +				return -EFAULT;
> +
> +			if (*awakened >= 0)
> +				return 1;
> +
> +			goto retry;
> +		}
> +
> +		if (uval != val) {
> +			spin_unlock(&bucket->lock);
> +
> +			bucket_dec_waiters(bucket);
> +			__set_current_state(TASK_RUNNING);
> +			*awakened = futex_dequeue_multiple(futexv, i);
> +
> +			if (*awakened >= 0)
> +				return 1;
> +
> +			return -EAGAIN;
> +		}
> +
> +		list_add_tail(&futexv->objects[i].list, &bucket->list);

and here

> +		spin_unlock(&bucket->lock);
> +	}
> +
> +	return 0;
> +}
> +

> +static void futex_mark_wake(struct futex_waiter *waiter,
> +			    struct futex_bucket *bucket,
> +			    struct wake_q_head *wake_q)
> +{
> +	struct task_struct *task;
> +	struct futexv_head *parent = futex_get_parent((uintptr_t)waiter,
> +						      waiter->index);
> +

	lockdep_assert_held(&bucket->lock);

> +	parent->hint = true;
> +	task = parent->task;
> +	get_task_struct(task);
> +	list_del_init_careful(&waiter->list);

and here

> +	wake_q_add_safe(wake_q, task);
> +	bucket_dec_waiters(bucket);
> +}


  parent reply	other threads:[~2021-02-16  9:38 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-15 15:23 [RFC PATCH 00/13] Add futex2 syscalls André Almeida
2021-02-15 15:23 ` [RFC PATCH 01/13] futex2: Implement wait and wake functions André Almeida
2021-02-15 19:59   ` Gabriel Krisman Bertazi
2021-02-18 13:29     ` André Almeida
2021-02-18 15:48       ` Gabriel Krisman Bertazi
2021-02-16  9:02   ` Peter Zijlstra
2021-02-18 20:09     ` André Almeida
2021-02-16  9:35   ` Peter Zijlstra [this message]
2021-02-16  9:56   ` Peter Zijlstra
2021-02-16 10:20     ` Sebastian Andrzej Siewior
2021-02-16 12:42       ` Peter Zijlstra
2021-02-16 22:12     ` Gabriel Krisman Bertazi
2021-02-15 15:23 ` [RFC PATCH 02/13] futex2: Add support for shared futexes André Almeida
2021-02-15 15:23 ` [RFC PATCH 03/13] futex2: Implement vectorized wait André Almeida
2021-02-15 20:03   ` Gabriel Krisman Bertazi
2021-02-15 20:06     ` Zebediah Figura
2021-02-15 20:08   ` Gabriel Krisman Bertazi
2021-02-15 15:23 ` [RFC PATCH 04/13] futex2: Implement requeue operation André Almeida
2021-02-15 15:23 ` [RFC PATCH 05/13] futex2: Add compatibility entry point for x86_x32 ABI André Almeida
2021-02-15 15:23 ` [RFC PATCH 06/13] docs: locking: futex2: Add documentation André Almeida
2021-02-16 18:34   ` Randy Dunlap
2021-02-18 19:12     ` André Almeida
2021-02-15 15:23 ` [RFC PATCH 07/13] selftests: futex2: Add wake/wait test André Almeida
2021-02-15 15:23 ` [RFC PATCH 08/13] selftests: futex2: Add timeout test André Almeida
2021-02-15 15:24 ` [RFC PATCH 09/13] selftests: futex2: Add wouldblock test André Almeida
2021-02-15 15:24 ` [RFC PATCH 10/13] selftests: futex2: Add waitv test André Almeida
2021-02-15 15:24 ` [RFC PATCH 11/13] selftests: futex2: Add requeue test André Almeida
2021-02-15 15:24 ` [RFC PATCH 12/13] perf bench: Add futex2 benchmark tests André Almeida
2021-02-15 15:24 ` [RFC PATCH 13/13] kernel: Enable waitpid() for futex2 André Almeida

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