From: Boaz Harrosh <openosd@gmail.com>
To: Patrick Farrell <pfarrell@whamcloud.com>,
Dave Chinner <david@fromorbit.com>, Jan Kara <jack@suse.cz>
Cc: Amir Goldstein <amir73il@gmail.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Kent Overstreet <kent.overstreet@gmail.com>,
Dave Chinner <dchinner@redhat.com>,
"Darrick J . Wong" <darrick.wong@oracle.com>,
Christoph Hellwig <hch@lst.de>,
Matthew Wilcox <willy@infradead.org>,
Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
linux-xfs <linux-xfs@vger.kernel.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
Josef Bacik <josef@toxicpanda.com>,
Alexander Viro <viro@zeniv.linux.org.uk>,
Andrew Morton <akpm@linux-foundation.org>
Subject: Re: pagecache locking
Date: Wed, 3 Jul 2019 04:25:53 +0300 [thread overview]
Message-ID: <9bc50b26-d424-d48a-16db-6fd7e0e88f79@gmail.com> (raw)
In-Reply-To: <DM6PR19MB250857CB8A3A1C8279D6F2F3C5FB0@DM6PR19MB2508.namprd19.prod.outlook.com>
On 03/07/2019 04:07, Patrick Farrell wrote:
> Recursively read locking is generally unsafe, that’s why lockdep
> complains about it. The common RW lock primitives are queued in
> their implementation, meaning this recursive read lock sequence:
> P1 - read (gets lock)
> P2 - write
> P1 - read
>
> Results not in a successful read lock, but P1 blocking behind P2,
> which is blocked behind P1.
> Readers are not allowed to jump past waiting writers.
OK thanks that makes sense. I did not know about that last part. Its a kind
of a lock fairness I did not know we have.
So I guess I'll keep my two locks than. The write_locker is the SLOW
path for me anyway, right?
[if we are already at the subject, Do mutexes have the same lock fairness as
above? Do the write_lock side of rw_sem have same fairness? Something I never
figured out]
Thanks
Boaz
>
> - Patrick
next prev parent reply other threads:[~2019-07-03 1:25 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20190610191420.27007-1-kent.overstreet@gmail.com>
[not found] ` <CAHk-=wi0iMHcO5nsYug06fV3-8s8fz7GDQWCuanefEGq6mHH1Q@mail.gmail.com>
[not found] ` <20190611011737.GA28701@kmo-pixel>
[not found] ` <20190611043336.GB14363@dread.disaster.area>
[not found] ` <20190612162144.GA7619@kmo-pixel>
[not found] ` <20190612230224.GJ14308@dread.disaster.area>
2019-06-13 18:36 ` pagecache locking (was: bcachefs status update) merged) Kent Overstreet
2019-06-13 21:13 ` Andreas Dilger
2019-06-13 21:21 ` Kent Overstreet
2019-06-14 0:35 ` Dave Chinner
2019-06-13 23:55 ` Dave Chinner
2019-06-14 2:30 ` Linus Torvalds
2019-06-14 7:30 ` Dave Chinner
2019-06-15 1:15 ` Linus Torvalds
2019-06-14 3:08 ` Linus Torvalds
2019-06-15 4:01 ` Linus Torvalds
2019-06-17 22:47 ` Dave Chinner
2019-06-17 23:38 ` Linus Torvalds
2019-06-18 4:21 ` Amir Goldstein
2019-06-19 10:38 ` Jan Kara
2019-06-19 22:37 ` Dave Chinner
2019-07-03 0:04 ` pagecache locking Boaz Harrosh
[not found] ` <DM6PR19MB250857CB8A3A1C8279D6F2F3C5FB0@DM6PR19MB2508.namprd19.prod.outlook.com>
2019-07-03 1:25 ` Boaz Harrosh [this message]
2019-07-05 23:31 ` Dave Chinner
2019-07-07 15:05 ` Boaz Harrosh
2019-07-07 23:55 ` Dave Chinner
2019-07-08 13:31 ` Jan Kara
2019-07-09 23:47 ` Dave Chinner
2019-07-10 8:41 ` Jan Kara
2019-06-14 17:08 ` pagecache locking (was: bcachefs status update) merged) Kent Overstreet
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