From: Matthew Wilcox <willy@infradead.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Jason Gunthorpe <jgg@ziepe.ca>, Christoph Hellwig <hch@lst.de>,
linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org,
Waiman Long <longman@redhat.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Will Deacon <will@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
linux-ext4@vger.kernel.org, cluster-devel@redhat.com,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: RFC: hold i_rwsem until aio completes
Date: Sat, 18 Jan 2020 14:40:35 -0800 [thread overview]
Message-ID: <20200118224035.GA26801@bombadil.infradead.org> (raw)
In-Reply-To: <20200115143347.GL2827@hirez.programming.kicks-ass.net>
On Wed, Jan 15, 2020 at 03:33:47PM +0100, Peter Zijlstra wrote:
> On Wed, Jan 15, 2020 at 09:24:28AM -0400, Jason Gunthorpe wrote:
>
> > I was interested because you are talking about allowing the read/write side
> > of a rw sem to be held across a return to user space/etc, which is the
> > same basic problem.
>
> No it is not; allowing the lock to be held across userspace doesn't
> change the owner. This is a crucial difference, PI depends on there
> being a distinct owner. That said, allowing the lock to be held across
> userspace still breaks PI in that it completely wrecks the ability to
> analyze the critical section.
Thinking about this from a PI point of view, the problem is not that we
returned to userspace still holding the lock, it's that boosting this
process's priority will not help release the lock faster because this
process no longer owns the lock.
If we had a lock owner handoff API (ie I can donate my lock to another
owner), that would solve this problem. We'd want to have special owners
to denote "RCU" "bottom halves" or "irq" so we know what we can do about
PI. I don't think we need a "I have stolen this lock from somebody else"
API, but maybe I'm wrong there.
next prev parent reply other threads:[~2020-01-18 22:41 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-14 16:12 RFC: hold i_rwsem until aio completes Christoph Hellwig
2020-01-14 16:12 ` [PATCH 01/12] mm: fix a comment in sys_swapon Christoph Hellwig
2020-02-10 23:29 ` Andrew Morton
2020-02-12 7:37 ` Christoph Hellwig
2020-01-14 16:12 ` [PATCH 02/12] locking/rwsem: Exit early when held by an anonymous owner Christoph Hellwig
2020-01-14 18:17 ` Waiman Long
2020-01-14 18:25 ` Christoph Hellwig
2020-01-14 18:33 ` Waiman Long
2020-01-14 18:55 ` Waiman Long
2020-01-14 16:12 ` [PATCH 03/12] xfs: fix IOCB_NOWAIT handling in xfs_file_dio_aio_read Christoph Hellwig
2020-01-14 16:12 ` [PATCH 04/12] gfs2: move setting current->backing_dev_info Christoph Hellwig
2020-01-14 16:12 ` [PATCH 05/12] gfs2: fix O_SYNC write handling Christoph Hellwig
2020-02-06 15:31 ` [Cluster-devel] " Andreas Gruenbacher
2020-01-14 16:12 ` [PATCH 06/12] iomap: pass a flags value to iomap_dio_rw Christoph Hellwig
2020-01-14 16:12 ` [PATCH 07/12] iomap: allow holding i_rwsem until aio completion Christoph Hellwig
2020-01-14 16:12 ` [PATCH 08/12] ext4: hold i_rwsem until AIO completes Christoph Hellwig
2020-01-14 21:50 ` Theodore Y. Ts'o
2020-01-15 6:48 ` Christoph Hellwig
2020-01-14 16:12 ` [PATCH 09/12] gfs2: " Christoph Hellwig
2020-01-14 16:12 ` [PATCH 10/12] xfs: " Christoph Hellwig
2020-01-14 16:12 ` [PATCH 11/12] xfs: don't set IOMAP_DIO_SYNCHRONOUS for unaligned I/O Christoph Hellwig
2020-01-14 16:12 ` [PATCH 12/12] iomap: remove the inode_dio_begin/end calls Christoph Hellwig
2020-01-14 18:47 ` RFC: hold i_rwsem until aio completes Matthew Wilcox
2020-01-15 6:54 ` Christoph Hellwig
2020-01-14 19:27 ` Jason Gunthorpe
2020-01-15 6:56 ` Christoph Hellwig
2020-01-15 13:24 ` Jason Gunthorpe
2020-01-15 14:33 ` Peter Zijlstra
2020-01-15 14:49 ` Jason Gunthorpe
2020-01-15 19:03 ` Waiman Long
2020-01-15 19:07 ` Christoph Hellwig
2020-01-18 22:40 ` Matthew Wilcox [this message]
2020-01-15 15:36 ` Christoph Hellwig
2020-01-15 16:26 ` Jason Gunthorpe
2020-01-16 14:00 ` Jan Kara
2020-02-03 17:44 ` Christoph Hellwig
2020-01-18 9:28 ` Dave Chinner
2020-02-03 17:46 ` Christoph Hellwig
2020-02-03 23:02 ` Dave Chinner
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