linux-kernel - Re: [PATCH 0/5] Fix races & improve the radix tree iterator patterns

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Date:	Wed, 3 Feb 2016 09:27:03 +0300
From:	Konstantin Khlebnikov <koct9i@...il.com>
To:	Matthew Wilcox <matthew.r.wilcox@...el.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Hugh Dickins <hughd@...gle.com>,
	Ohad Ben-Cohen <ohad@...ery.com>,
	Matthew Wilcox <willy@...ux.intel.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [PATCH 0/5] Fix races & improve the radix tree iterator patterns

On Thu, Jan 28, 2016 at 10:17 AM, Konstantin Khlebnikov
<koct9i@...il.com> wrote:
> On Thu, Jan 28, 2016 at 12:17 AM, Matthew Wilcox
> <matthew.r.wilcox@...el.com> wrote:
>> From: Matthew Wilcox <willy@...ux.intel.com>
>>
>> The first two patches here are bugfixes, and I would like to see them
>> make their way into stable ASAP since they can lead to data corruption
>> (very low probabilty).
>>
>> The last three patches do not qualify as bugfixes.  They simply improve
>> the standard pattern used to do radix tree iterations by removing the
>> 'goto restart' part.  Partially this is because this is an ugly &
>> confusing goto, and partially because with multi-order entries in the
>> tree, it'll be more likely that we'll see an indirect_ptr bit, and
>> it's more efficient to kep going from the point of the iteration we're
>> currently in than restart from the beginning each time.
>
> Ack  whole set.
>
> I think we should go deeper in hide dereference/retry inside iterator.
> Something like radix_tree_for_each_data(data, slot, root, iter, start).
> I'll prepare patch for that.

After second thought: there'ra not so many users for new sugar.
This scheme with radix_tree_deref_retry - radix_tree_iter_retry
complicated but fine.

>
>>
>> Matthew Wilcox (5):
>>   radix-tree: Fix race in gang lookup
>>   hwspinlock: Fix race between radix tree insertion and lookup
>>   btrfs: Use radix_tree_iter_retry()
>>   mm: Use radix_tree_iter_retry()
>>   radix-tree,shmem: Introduce radix_tree_iter_next()
>>
>>  drivers/hwspinlock/hwspinlock_core.c |  4 +++
>>  fs/btrfs/tests/btrfs-tests.c         |  3 +-
>>  include/linux/radix-tree.h           | 31 +++++++++++++++++++++
>>  lib/radix-tree.c                     | 12 ++++++--
>>  mm/filemap.c                         | 53 ++++++++++++------------------------
>>  mm/shmem.c                           | 30 ++++++++++----------
>>  6 files changed, 78 insertions(+), 55 deletions(-)
>>
>> --
>> 2.7.0.rc3
>>
>> --
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