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From: Eric Biggers <ebiggers@kernel.org>
To: Siddh Raman Pant <code@siddh.me>
Cc: "christophe.jaillet" <christophe.jaillet@wanadoo.fr>,
	corbet <corbet@lwn.net>, dhowells <dhowells@redhat.com>,
	edumazet <edumazet@google.com>,
	linux-kernel-mentees 
	<linux-kernel-mentees@lists.linuxfoundation.org>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	mchehab <mchehab@kernel.org>, rdunlap <rdunlap@infradead.org>
Subject: Re: [PATCH v2 3/3] kernel/watch_queue: Remove wqueue->defunct and use pipe for clear check
Date: Fri, 5 Aug 2022 18:33:20 +0000	[thread overview]
Message-ID: <Yu1icG/o8VcfsQdy@gmail.com> (raw)
In-Reply-To: <1826d5c4a90.282ac4bf118702.5300662644268737477@siddh.me>

On Fri, Aug 05, 2022 at 03:05:41PM +0530, Siddh Raman Pant wrote:
> On Fri, 05 Aug 2022 12:54:31 +0530  Eric Biggers  wrote:
> > Why is the READ_ONCE() needed?  Doesn't wqueue->lock protect wqueue->pipe?
> 
> We are changing the pointer while a notification can be potentially waiting to
> be posted to the pipe. So a barrier is needed to prevent compiler magic from
> reloading the value.
> 

wqueue->pipe is only read or written while wqueue->lock is held, so that is not
an issue at all.

- Eric

WARNING: multiple messages have this Message-ID (diff)
From: Eric Biggers <ebiggers@kernel.org>
To: Siddh Raman Pant <code@siddh.me>
Cc: corbet <corbet@lwn.net>, rdunlap <rdunlap@infradead.org>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	dhowells <dhowells@redhat.com>, edumazet <edumazet@google.com>,
	"christophe.jaillet" <christophe.jaillet@wanadoo.fr>,
	mchehab <mchehab@kernel.org>,
	linux-kernel-mentees
	<linux-kernel-mentees@lists.linuxfoundation.org>
Subject: Re: [PATCH v2 3/3] kernel/watch_queue: Remove wqueue->defunct and use pipe for clear check
Date: Fri, 5 Aug 2022 18:33:20 +0000	[thread overview]
Message-ID: <Yu1icG/o8VcfsQdy@gmail.com> (raw)
In-Reply-To: <1826d5c4a90.282ac4bf118702.5300662644268737477@siddh.me>

On Fri, Aug 05, 2022 at 03:05:41PM +0530, Siddh Raman Pant wrote:
> On Fri, 05 Aug 2022 12:54:31 +0530  Eric Biggers  wrote:
> > Why is the READ_ONCE() needed?  Doesn't wqueue->lock protect wqueue->pipe?
> 
> We are changing the pointer while a notification can be potentially waiting to
> be posted to the pipe. So a barrier is needed to prevent compiler magic from
> reloading the value.
> 

wqueue->pipe is only read or written while wqueue->lock is held, so that is not
an issue at all.

- Eric
_______________________________________________
Linux-kernel-mentees mailing list
Linux-kernel-mentees@lists.linuxfoundation.org
https://lists.linuxfoundation.org/mailman/listinfo/linux-kernel-mentees

  reply	other threads:[~2022-08-05 18:33 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-08-04 13:30 [PATCH 0/3] kernel/watch_queue: Clean up some code Siddh Raman Pant via Linux-kernel-mentees
2022-08-04 13:30 ` Siddh Raman Pant
2022-08-04 13:30 ` [PATCH 1/3 v4] kernel/watch_queue: Remove dangling pipe reference while clearing watch_queue Siddh Raman Pant via Linux-kernel-mentees
2022-08-04 13:30   ` Siddh Raman Pant
2022-08-04 13:30 ` [PATCH 2/3] kernel/watch_queue: Improve struct annotation formatting Siddh Raman Pant via Linux-kernel-mentees
2022-08-04 13:30   ` Siddh Raman Pant
2022-08-05  7:22   ` Eric Biggers
2022-08-05  7:22     ` Eric Biggers
2022-08-05  9:35     ` Siddh Raman Pant via Linux-kernel-mentees
2022-08-05  9:35       ` Siddh Raman Pant
2022-08-04 13:30 ` [PATCH 3/3] kernel/watch_queue: Remove wqueue->defunct and use pipe for clear check Siddh Raman Pant via Linux-kernel-mentees
2022-08-04 13:30   ` Siddh Raman Pant
2022-08-04 14:41   ` [PATCH v2 " Siddh Raman Pant via Linux-kernel-mentees
2022-08-04 14:41     ` Siddh Raman Pant
2022-08-05  7:24     ` Eric Biggers
2022-08-05  7:24       ` Eric Biggers
2022-08-05  9:35       ` Siddh Raman Pant via Linux-kernel-mentees
2022-08-05  9:35         ` Siddh Raman Pant
2022-08-05 18:33         ` Eric Biggers [this message]
2022-08-05 18:33           ` Eric Biggers
2022-08-06  7:23           ` Siddh Raman Pant
2022-08-06  7:23             ` Siddh Raman Pant via Linux-kernel-mentees
2022-08-05  7:16 ` [PATCH 0/3] kernel/watch_queue: Clean up some code Eric Biggers
2022-08-05  7:16   ` Eric Biggers
2022-08-05  9:35   ` Siddh Raman Pant via Linux-kernel-mentees
2022-08-05  9:35     ` Siddh Raman Pant

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