From: David Sterba <dsterba@suse.cz>
To: Nikolay Borisov <nborisov@suse.com>
Cc: David Sterba <dsterba@suse.com>, linux-btrfs@vger.kernel.org
Subject: Re: [PATCH 3/5] btrfs: access eb::blocking_writers according to ACCESS_ONCE policies
Date: Tue, 29 Oct 2019 22:33:01 +0100 [thread overview]
Message-ID: <20191029213301.GC3001@twin.jikos.cz> (raw)
In-Reply-To: <270b6d1b-9304-80cd-4104-b55e8df99a8a@suse.com>
On Wed, Oct 23, 2019 at 11:42:29AM +0300, Nikolay Borisov wrote:
> On 17.10.19 г. 22:38 ч., David Sterba wrote:
> > @@ -294,7 +299,8 @@ void btrfs_tree_lock(struct extent_buffer *eb)
> > */
> > void btrfs_tree_unlock(struct extent_buffer *eb)
> > {
> > - int blockers = eb->blocking_writers;
> > + /* This is read both locked and unlocked */
> > + int blockers = READ_ONCE(eb->blocking_writers);
>
> Actually aren't we guaranteed that btrfs_tree_unlock's caller is the
> owner of blocking_writers meaning we can use plain loads as per:
>
> "The owning CPU or thread may use plain loads..."
That's right, I'll remove READ_ONCE and leave a comment as it's not
obvious from the context.
next prev parent reply other threads:[~2019-10-29 21:32 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-17 19:38 [PATCH 0/5] Extent buffer locking and documentation David Sterba
2019-10-17 19:38 ` [PATCH 1/5] btrfs: merge blocking_writers branches in btrfs_tree_read_lock David Sterba
2019-10-17 19:38 ` [PATCH 2/5] btrfs: set blocking_writers directly, no increment or decrement David Sterba
2019-10-18 12:08 ` Nikolay Borisov
2019-10-18 17:31 ` David Sterba
2019-10-17 19:38 ` [PATCH 3/5] btrfs: access eb::blocking_writers according to ACCESS_ONCE policies David Sterba
2019-10-23 8:42 ` Nikolay Borisov
2019-10-29 21:33 ` David Sterba [this message]
2019-10-17 19:39 ` [PATCH 4/5] btrfs: serialize blocking_writers updates David Sterba
2019-10-23 9:57 ` Nikolay Borisov
2019-10-29 17:51 ` David Sterba
2019-10-29 18:48 ` Nikolay Borisov
2019-10-29 21:15 ` David Sterba
2019-10-17 19:39 ` [PATCH 5/5] btrfs: document extent buffer locking David Sterba
2019-10-18 0:17 ` Qu Wenruo
2019-10-18 11:56 ` David Sterba
2019-10-22 9:53 ` Nikolay Borisov
2019-10-22 10:41 ` David Sterba
2019-10-23 11:16 ` Nikolay Borisov
2019-10-29 17:33 ` David Sterba
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