From: NeilBrown <nfbrown@novell.com>
To: Jan Kara <jack@suse.cz>, linux-fsdevel@vger.kernel.org
Cc: linux-ext4@vger.kernel.org, linux-mm@kvack.org,
Ross Zwisler <ross.zwisler@linux.intel.com>,
Dan Williams <dan.j.williams@intel.com>,
linux-nvdimm@lists.01.org, Matthew Wilcox <willy@linux.intel.com>
Subject: Re: [PATCH 16/18] dax: New fault locking
Date: Wed, 27 Apr 2016 14:27:59 +1000 [thread overview]
Message-ID: <87h9enwu9c.fsf@notabene.neil.brown.name> (raw)
In-Reply-To: <1461015341-20153-17-git-send-email-jack@suse.cz>
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On Tue, Apr 19 2016, Jan Kara wrote:
> Currently DAX page fault locking is racy.
>
> CPU0 (write fault) CPU1 (read fault)
>
> __dax_fault() __dax_fault()
> get_block(inode, block, &bh, 0) -> not mapped
> get_block(inode, block, &bh, 0)
> -> not mapped
> if (!buffer_mapped(&bh))
> if (vmf->flags & FAULT_FLAG_WRITE)
> get_block(inode, block, &bh, 1) -> allocates blocks
> if (page) -> no
> if (!buffer_mapped(&bh))
> if (vmf->flags & FAULT_FLAG_WRITE) {
> } else {
> dax_load_hole();
> }
> dax_insert_mapping()
>
> And we are in a situation where we fail in dax_radix_entry() with -EIO.
>
> Another problem with the current DAX page fault locking is that there is
> no race-free way to clear dirty tag in the radix tree. We can always
> end up with clean radix tree and dirty data in CPU cache.
>
> We fix the first problem by introducing locking of exceptional radix
> tree entries in DAX mappings acting very similarly to page lock and thus
> synchronizing properly faults against the same mapping index. The same
> lock can later be used to avoid races when clearing radix tree dirty
> tag.
>
> Signed-off-by: Jan Kara <jack@suse.cz>
Reviewed-by: NeilBrown <neilb@suse.com> (for the exception locking bits)
I really like how you have structured the code - makes it fairly
obviously correct!
Thanks,
NeilBrown
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WARNING: multiple messages have this Message-ID (diff)
From: NeilBrown <nfbrown@novell.com>
To: Jan Kara <jack@suse.cz>, linux-fsdevel@vger.kernel.org
Cc: linux-ext4@vger.kernel.org, linux-mm@kvack.org,
Ross Zwisler <ross.zwisler@linux.intel.com>,
Dan Williams <dan.j.williams@intel.com>,
linux-nvdimm@lists.01.org, Matthew Wilcox <willy@linux.intel.com>,
Jan Kara <jack@suse.cz>
Subject: Re: [PATCH 16/18] dax: New fault locking
Date: Wed, 27 Apr 2016 14:27:59 +1000 [thread overview]
Message-ID: <87h9enwu9c.fsf@notabene.neil.brown.name> (raw)
In-Reply-To: <1461015341-20153-17-git-send-email-jack@suse.cz>
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On Tue, Apr 19 2016, Jan Kara wrote:
> Currently DAX page fault locking is racy.
>
> CPU0 (write fault) CPU1 (read fault)
>
> __dax_fault() __dax_fault()
> get_block(inode, block, &bh, 0) -> not mapped
> get_block(inode, block, &bh, 0)
> -> not mapped
> if (!buffer_mapped(&bh))
> if (vmf->flags & FAULT_FLAG_WRITE)
> get_block(inode, block, &bh, 1) -> allocates blocks
> if (page) -> no
> if (!buffer_mapped(&bh))
> if (vmf->flags & FAULT_FLAG_WRITE) {
> } else {
> dax_load_hole();
> }
> dax_insert_mapping()
>
> And we are in a situation where we fail in dax_radix_entry() with -EIO.
>
> Another problem with the current DAX page fault locking is that there is
> no race-free way to clear dirty tag in the radix tree. We can always
> end up with clean radix tree and dirty data in CPU cache.
>
> We fix the first problem by introducing locking of exceptional radix
> tree entries in DAX mappings acting very similarly to page lock and thus
> synchronizing properly faults against the same mapping index. The same
> lock can later be used to avoid races when clearing radix tree dirty
> tag.
>
> Signed-off-by: Jan Kara <jack@suse.cz>
Reviewed-by: NeilBrown <neilb@suse.com> (for the exception locking bits)
I really like how you have structured the code - makes it fairly
obviously correct!
Thanks,
NeilBrown
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next prev parent reply other threads:[~2016-04-27 4:27 UTC|newest]
Thread overview: 122+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-04-18 21:35 [RFC v3] [PATCH 0/18] DAX page fault locking Jan Kara
2016-04-18 21:35 ` Jan Kara
2016-04-18 21:35 ` [PATCH 01/18] ext4: Handle transient ENOSPC properly for DAX Jan Kara
2016-04-18 21:35 ` Jan Kara
2016-04-18 21:35 ` [PATCH 02/18] ext4: Fix race in transient ENOSPC detection Jan Kara
2016-04-18 21:35 ` Jan Kara
2016-04-18 21:35 ` [PATCH 03/18] DAX: move RADIX_DAX_ definitions to dax.c Jan Kara
2016-04-18 21:35 ` Jan Kara
2016-04-18 21:35 ` [PATCH 04/18] dax: Remove complete_unwritten argument Jan Kara
2016-04-18 21:35 ` Jan Kara
2016-04-18 21:35 ` [PATCH 05/18] ext2: Avoid DAX zeroing to corrupt data Jan Kara
2016-04-18 21:35 ` Jan Kara
2016-04-29 16:30 ` Ross Zwisler
2016-04-29 16:30 ` Ross Zwisler
2016-04-29 16:30 ` Ross Zwisler
2016-04-18 21:35 ` [PATCH 06/18] dax: Remove dead zeroing code from fault handlers Jan Kara
2016-04-18 21:35 ` Jan Kara
2016-04-29 16:48 ` Ross Zwisler
2016-04-18 21:35 ` [PATCH 07/18] ext4: Refactor direct IO code Jan Kara
2016-04-18 21:35 ` Jan Kara
2016-04-18 21:35 ` Jan Kara
2016-04-18 21:35 ` [PATCH 08/18] ext4: Pre-zero allocated blocks for DAX IO Jan Kara
2016-04-18 21:35 ` Jan Kara
2016-04-18 21:35 ` Jan Kara
2016-04-29 18:01 ` Ross Zwisler
2016-04-29 18:01 ` Ross Zwisler
2016-04-29 18:01 ` Ross Zwisler
2016-05-02 13:09 ` Jan Kara
2016-05-02 13:09 ` Jan Kara
2016-04-18 21:35 ` [PATCH 09/18] dax: Remove zeroing from dax_io() Jan Kara
2016-04-18 21:35 ` Jan Kara
2016-04-18 21:35 ` Jan Kara
2016-04-29 18:56 ` Ross Zwisler
2016-04-29 18:56 ` Ross Zwisler
2016-04-18 21:35 ` [PATCH 10/18] dax: Remove pointless writeback from dax_do_io() Jan Kara
2016-04-18 21:35 ` Jan Kara
2016-04-18 21:35 ` Jan Kara
2016-04-29 19:00 ` Ross Zwisler
2016-04-29 19:00 ` Ross Zwisler
2016-04-29 19:00 ` Ross Zwisler
2016-04-18 21:35 ` [PATCH 11/18] dax: Fix condition for filling of PMD holes Jan Kara
2016-04-18 21:35 ` Jan Kara
2016-04-29 19:08 ` Ross Zwisler
2016-04-29 19:08 ` Ross Zwisler
2016-04-29 19:08 ` Ross Zwisler
2016-05-02 13:16 ` Jan Kara
2016-05-02 13:16 ` Jan Kara
2016-04-18 21:35 ` [PATCH 12/18] dax: Remove redundant inode size checks Jan Kara
2016-04-18 21:35 ` Jan Kara
2016-04-18 21:35 ` Jan Kara
2016-04-18 21:35 ` [PATCH 13/18] dax: Make huge page handling depend of CONFIG_BROKEN Jan Kara
2016-04-18 21:35 ` Jan Kara
2016-04-18 21:35 ` Jan Kara
2016-04-29 19:53 ` Ross Zwisler
2016-04-29 19:53 ` Ross Zwisler
2016-05-02 13:19 ` Jan Kara
2016-05-02 13:19 ` Jan Kara
2016-05-02 13:19 ` Jan Kara
2016-04-18 21:35 ` [PATCH 14/18] dax: Define DAX lock bit for radix tree exceptional entry Jan Kara
2016-04-18 21:35 ` Jan Kara
2016-04-18 21:35 ` Jan Kara
2016-04-29 20:03 ` Ross Zwisler
2016-04-29 20:03 ` Ross Zwisler
2016-04-29 20:03 ` Ross Zwisler
2016-04-18 21:35 ` [PATCH 15/18] dax: Allow DAX code to replace exceptional entries Jan Kara
2016-04-18 21:35 ` Jan Kara
2016-04-18 21:35 ` Jan Kara
2016-04-29 20:29 ` Ross Zwisler
2016-04-29 20:29 ` Ross Zwisler
2016-04-18 21:35 ` [PATCH 16/18] dax: New fault locking Jan Kara
2016-04-18 21:35 ` Jan Kara
2016-04-27 4:27 ` NeilBrown [this message]
2016-04-27 4:27 ` NeilBrown
2016-05-06 4:13 ` Ross Zwisler
2016-05-06 4:13 ` Ross Zwisler
2016-05-06 4:13 ` Ross Zwisler
2016-05-10 12:27 ` Jan Kara
2016-05-10 12:27 ` Jan Kara
2016-05-11 19:26 ` Ross Zwisler
2016-05-11 19:26 ` Ross Zwisler
2016-05-12 7:58 ` Jan Kara
2016-05-12 7:58 ` Jan Kara
2016-04-18 21:35 ` [PATCH 17/18] dax: Use radix tree entry lock to protect cow faults Jan Kara
2016-04-18 21:35 ` Jan Kara
2016-04-18 21:35 ` Jan Kara
2016-04-19 11:46 ` Jerome Glisse
2016-04-19 11:46 ` Jerome Glisse
2016-04-19 11:46 ` Jerome Glisse
2016-04-19 14:33 ` Jan Kara
2016-04-19 14:33 ` Jan Kara
2016-04-19 14:33 ` Jan Kara
2016-04-19 15:19 ` Jerome Glisse
2016-04-19 15:19 ` Jerome Glisse
2016-04-19 15:19 ` Jerome Glisse
2016-04-19 15:19 ` Jerome Glisse
2016-04-18 21:35 ` [PATCH 18/18] dax: Remove i_mmap_lock protection Jan Kara
2016-04-18 21:35 ` Jan Kara
2016-04-18 21:35 ` Jan Kara
2016-05-06 3:35 ` [RFC v3] [PATCH 0/18] DAX page fault locking Ross Zwisler
2016-05-06 3:35 ` Ross Zwisler
2016-05-06 20:33 ` Ross Zwisler
2016-05-06 20:33 ` Ross Zwisler
2016-05-09 9:38 ` Jan Kara
2016-05-09 9:38 ` Jan Kara
2016-05-09 9:38 ` Jan Kara
2016-05-10 15:28 ` Jan Kara
2016-05-10 15:28 ` Jan Kara
2016-05-10 15:28 ` Jan Kara
2016-05-10 20:30 ` Ross Zwisler
2016-05-10 20:30 ` Ross Zwisler
2016-05-10 20:30 ` Ross Zwisler
2016-05-10 22:39 ` Ross Zwisler
2016-05-10 22:39 ` Ross Zwisler
2016-05-11 9:19 ` Jan Kara
2016-05-11 9:19 ` Jan Kara
2016-05-11 9:19 ` Jan Kara
2016-05-11 15:52 ` Ross Zwisler
2016-05-11 15:52 ` Ross Zwisler
2016-05-11 15:52 ` Ross Zwisler
2016-05-09 21:28 ` Verma, Vishal L
2016-05-10 11:52 ` Jan Kara
2016-05-10 11:52 ` Jan Kara
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