From: Matthew Wilcox <willy@infradead.org>
To: Andreas Gruenbacher <agruenba@redhat.com>
Cc: Steven Whitehouse <swhiteho@redhat.com>,
Bob Peterson <rpeterso@redhat.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Alexander Viro <viro@zeniv.linux.org.uk>,
Christoph Hellwig <hch@infradead.org>,
"Darrick J. Wong" <djwong@kernel.org>, Jan Kara <jack@suse.cz>,
LKML <linux-kernel@vger.kernel.org>,
cluster-devel <cluster-devel@redhat.com>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
ocfs2-devel@oss.oracle.com
Subject: Re: [Cluster-devel] [PATCH v6 10/19] gfs2: Introduce flag for glock holder auto-demotion
Date: Mon, 23 Aug 2021 17:05:27 +0100 [thread overview]
Message-ID: <YSPHR7EL/ujG0Of7@casper.infradead.org> (raw)
In-Reply-To: <CAHc6FU5uHJSXD+CQk3W9BfZmnBCd+fqHt4Bd+=uVH18rnYCPLg@mail.gmail.com>
On Mon, Aug 23, 2021 at 05:18:12PM +0200, Andreas Gruenbacher wrote:
> On Mon, Aug 23, 2021 at 10:14 AM Steven Whitehouse <swhiteho@redhat.com> wrote:
> > If the goal here is just to allow the glock to be held for a longer
> > period of time, but with occasional interruptions to prevent
> > starvation, then we have a potential model for this. There is
> > cond_resched_lock() which does this for spin locks.
>
> This isn't an appropriate model for what I'm trying to achieve here.
> In the cond_resched case, we know at the time of the cond_resched call
> whether or not we want to schedule. If we do, we want to drop the spin
> lock, schedule, and then re-acquire the spin lock. In the case we're
> looking at here, we want to fault in user pages. There is no way of
> knowing beforehand if the glock we're currently holding will have to
> be dropped to achieve that. In fact, it will almost never have to be
> dropped. But if it does, we need to drop it straight away to allow the
> conflicting locking request to succeed.
It occurs to me that this is similar to the wound/wait mutexes
(include/linux/ww_mutex.h & Documentation/locking/ww-mutex-design.rst).
You want to mark the glock as woundable before faulting, and then discover
if it was wounded after faulting. Maybe sharing this terminology will
aid in understanding?
next prev parent reply other threads:[~2021-08-23 16:07 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-19 19:40 [PATCH v6 00/19] gfs2: Fix mmap + page fault deadlocks Andreas Gruenbacher
2021-08-19 19:40 ` [PATCH v6 01/19] iov_iter: Fix iov_iter_get_pages{,_alloc} page fault return value Andreas Gruenbacher
2021-08-19 19:40 ` [PATCH v6 02/19] powerpc/kvm: Fix kvm_use_magic_page Andreas Gruenbacher
2021-08-19 19:40 ` [PATCH v6 03/19] Turn fault_in_pages_{readable,writeable} into fault_in_{readable,writeable} Andreas Gruenbacher
2021-08-19 19:40 ` [PATCH v6 04/19] Turn iov_iter_fault_in_readable into fault_in_iov_iter_readable Andreas Gruenbacher
2021-08-19 19:40 ` [PATCH v6 05/19] iov_iter: Introduce fault_in_iov_iter_writeable Andreas Gruenbacher
2021-08-19 19:40 ` [PATCH v6 06/19] gfs2: Add wrapper for iomap_file_buffered_write Andreas Gruenbacher
2021-08-19 19:40 ` [PATCH v6 07/19] gfs2: Clean up function may_grant Andreas Gruenbacher
2021-08-19 19:40 ` [PATCH v6 08/19] gfs2: Eliminate vestigial HIF_FIRST Andreas Gruenbacher
2021-08-19 19:40 ` [PATCH v6 09/19] gfs2: Remove redundant check from gfs2_glock_dq Andreas Gruenbacher
2021-08-19 19:40 ` [PATCH v6 10/19] gfs2: Introduce flag for glock holder auto-demotion Andreas Gruenbacher
2021-08-20 9:35 ` [Cluster-devel] " Steven Whitehouse
2021-08-20 13:11 ` Bob Peterson
2021-08-20 13:41 ` Steven Whitehouse
2021-08-20 15:22 ` Andreas Gruenbacher
2021-08-23 8:14 ` Steven Whitehouse
2021-08-23 15:18 ` Andreas Gruenbacher
2021-08-23 16:05 ` Matthew Wilcox [this message]
2021-08-23 16:36 ` Bob Peterson
2021-08-23 19:12 ` Andreas Gruenbacher
2021-08-24 7:59 ` Steven Whitehouse
2021-08-20 13:17 ` Andreas Gruenbacher
2021-08-20 13:47 ` Steven Whitehouse
2021-08-20 14:43 ` Andreas Grünbacher
2021-08-19 19:40 ` [PATCH v6 11/19] gfs2: Move the inode glock locking to gfs2_file_buffered_write Andreas Gruenbacher
2021-08-19 19:40 ` [PATCH v6 12/19] gfs2: Fix mmap + page fault deadlocks for buffered I/O Andreas Gruenbacher
2021-08-19 19:40 ` [PATCH v6 13/19] iomap: Fix iomap_dio_rw return value for user copies Andreas Gruenbacher
2021-08-19 19:40 ` [PATCH v6 14/19] iomap: Support partial direct I/O on user copy failures Andreas Gruenbacher
2021-08-19 19:40 ` [PATCH v6 15/19] iomap: Add done_before argument to iomap_dio_rw Andreas Gruenbacher
2021-08-19 19:40 ` [PATCH v6 16/19] gup: Introduce FOLL_NOFAULT flag to disable page faults Andreas Gruenbacher
2021-08-19 19:41 ` [PATCH v6 17/19] iov_iter: Introduce nofault " Andreas Gruenbacher
2021-08-19 19:41 ` [PATCH v6 18/19] gfs2: Fix mmap + page fault deadlocks for direct I/O Andreas Gruenbacher
2021-08-19 19:41 ` [PATCH v6 19/19] gfs2: Eliminate ip->i_gh Andreas Gruenbacher
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