From: Siddh Raman Pant via Linux-kernel-mentees <linux-kernel-mentees@lists.linuxfoundation.org>
To: "Eric Biggers" <ebiggers@kernel.org>
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, 05 Aug 2022 15:05:41 +0530 [thread overview]
Message-ID: <1826d5c4a90.282ac4bf118702.5300662644268737477@siddh.me> (raw)
In-Reply-To: <YuzFrzrTnTtUHMn/@sol.localdomain>
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.
This was remarked by David Howells here:
https://lore.kernel.org/lkml/3558070.1658933200@warthog.procyon.org.uk/
> This isn't the correct block comment format; it should look like:
>
> /*
> * This pipe will get freed by the caller free_pipe_info().
> * Removing this reference also prevents new notifications.
> */
>
> - Eric
>
Okay, will make the change.
Thanks,
Siddh
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WARNING: multiple messages have this Message-ID (diff)
From: Siddh Raman Pant <code@siddh.me>
To: "Eric Biggers" <ebiggers@kernel.org>
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, 05 Aug 2022 15:05:41 +0530 [thread overview]
Message-ID: <1826d5c4a90.282ac4bf118702.5300662644268737477@siddh.me> (raw)
In-Reply-To: <YuzFrzrTnTtUHMn/@sol.localdomain>
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.
This was remarked by David Howells here:
https://lore.kernel.org/lkml/3558070.1658933200@warthog.procyon.org.uk/
> This isn't the correct block comment format; it should look like:
>
> /*
> * This pipe will get freed by the caller free_pipe_info().
> * Removing this reference also prevents new notifications.
> */
>
> - Eric
>
Okay, will make the change.
Thanks,
Siddh
next prev parent reply other threads:[~2022-08-05 9:36 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 [this message]
2022-08-05 9:35 ` Siddh Raman Pant
2022-08-05 18:33 ` Eric Biggers
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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