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From: Linus Torvalds <torvalds@linux-foundation.org>
To: Dave Chinner <david@fromorbit.com>
Cc: Kent Overstreet <kent.overstreet@gmail.com>,
	Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	linux-bcache@vger.kernel.org, Dave Chinner <dchinner@redhat.com>,
	"Darrick J . Wong" <darrick.wong@oracle.com>,
	Zach Brown <zach.brown@ni.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Jens Axboe <axboe@kernel.dk>, Josef Bacik <josef@toxicpanda.com>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Andrew Morton <akpm@linux-foundation.org>,
	Tejun Heo <tj@kernel.org>
Subject: Re: bcachefs status update (it's done cooking; let's get this sucker merged)
Date: Mon, 10 Jun 2019 18:39:00 -1000	[thread overview]
Message-ID: <CAHk-=whDmeozRHUO0qM+2OeGw+=dkcjwGdsvms-x5Dz4y7Tzcw@mail.gmail.com> (raw)
In-Reply-To: <20190611041045.GA14363@dread.disaster.area>

On Mon, Jun 10, 2019 at 6:11 PM Dave Chinner <david@fromorbit.com> wrote:
>
> Please, no, let's not make the rwsems even more fragile than they
> already are. I'm tired of the ongoing XFS customer escalations that
> end up being root caused to yet another rwsem memory barrier bug.
>
> > Have you talked to Waiman Long about that?
>
> Unfortunately, Waiman has been unable to find/debug multiple rwsem
> exclusion violations we've seen in XFS bug reports over the past 2-3
> years.

Inside xfs you can do whatever you want.

But in generic code, no, we're not saying "we don't trust the generic
locking, so we cook our own random locking".

If tghere really are exclusion issues, they should be fairly easy to
try to find with a generic test-suite. Have a bunch of readers that
assert that some shared variable has a particular value, and a bund of
writers that then modify the value and set it back. Add some random
timing and "yield" to them all, and show that the serialization is
wrong.

Some kind of "XFS load Y shows problems" is undebuggable, and not
necessarily due to locking.

Because if the locking issues are real (and we did fix one bug
recently in a9e9bcb45b15: "locking/rwsem: Prevent decrement of reader
count before increment") it needs to be fixed. Some kind of "let's do
something else entirely" is simply not acceptable.

                  Linus

  reply	other threads:[~2019-06-11  4:39 UTC|newest]

Thread overview: 63+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-06-10 19:14 bcachefs status update (it's done cooking; let's get this sucker merged) Kent Overstreet
2019-06-10 19:14 ` [PATCH 01/12] Compiler Attributes: add __flatten Kent Overstreet
2019-06-12 17:16   ` Greg KH
2019-06-10 19:14 ` [PATCH 02/12] locking: SIX locks (shared/intent/exclusive) Kent Overstreet
2019-06-10 19:14 ` [PATCH 03/12] mm: pagecache add lock Kent Overstreet
2019-06-10 19:14 ` [PATCH 04/12] mm: export find_get_pages() Kent Overstreet
2019-06-10 19:14 ` [PATCH 05/12] fs: insert_inode_locked2() Kent Overstreet
2019-06-10 19:14 ` [PATCH 06/12] fs: factor out d_mark_tmpfile() Kent Overstreet
2019-06-10 19:14 ` [PATCH 07/12] Propagate gfp_t when allocating pte entries from __vmalloc Kent Overstreet
2019-06-10 19:14 ` [PATCH 08/12] block: Add some exports for bcachefs Kent Overstreet
2019-06-10 19:14 ` [PATCH 09/12] bcache: optimize continue_at_nobarrier() Kent Overstreet
2019-06-10 19:14 ` [PATCH 10/12] bcache: move closures to lib/ Kent Overstreet
2019-06-11 10:25   ` Coly Li
2019-06-13  7:28   ` Christoph Hellwig
2019-06-13 11:04     ` Kent Overstreet
2019-06-10 19:14 ` [PATCH 11/12] closures: closure_wait_event() Kent Overstreet
2019-06-11 10:25   ` Coly Li
2019-06-12 17:17   ` Greg KH
2019-06-10 19:14 ` [PATCH 12/12] closures: fix a race on wakeup from closure_sync Kent Overstreet
2019-07-16 10:47   ` Coly Li
2019-07-18  7:46     ` Coly Li
2019-07-22 17:22       ` Kent Overstreet
2019-06-10 20:46 ` bcachefs status update (it's done cooking; let's get this sucker merged) Linus Torvalds
2019-06-11  1:17   ` Kent Overstreet
2019-06-11  4:33     ` Dave Chinner
2019-06-12 16:21       ` Kent Overstreet
2019-06-12 23:02         ` Dave Chinner
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
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
2019-06-19  8:21           ` bcachefs status update (it's done cooking; let's get this sucker merged) Jan Kara
2019-07-03  1:04             ` [PATCH] mm: Support madvise_willneed override by Filesystems Boaz Harrosh
2019-07-03 17:21               ` Jan Kara
2019-07-03 18:03                 ` Boaz Harrosh
2019-06-11  4:55     ` bcachefs status update (it's done cooking; let's get this sucker merged) Linus Torvalds
2019-06-11 14:26       ` Matthew Wilcox
2019-06-11  4:10   ` Dave Chinner
2019-06-11  4:39     ` Linus Torvalds [this message]
2019-06-11  7:10       ` Dave Chinner
2019-06-12  2:07         ` Linus Torvalds
2019-07-03  5:59 ` Stefan K
2019-06-29 16:39 Luke Kenneth Casson Leighton

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