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From: Ross Zwisler <ross.zwisler@linux.intel.com>
To: Jan Kara <jack@suse.cz>
Cc: linux-nvdimm@lists.01.org, Ted Tso <tytso@mit.edu>,
	linux-ext4@vger.kernel.org,
	Vishal Verma <vishal.l.verma@intel.com>,
	Ross Zwisler <ross.zwisler@linux.intel.com>,
	Dan Williams <dan.j.williams@intel.com>,
	linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH 2/7] dax: Make huge page handling depend of CONFIG_BROKEN
Date: Thu, 12 May 2016 12:59:58 -0600	[thread overview]
Message-ID: <20160512185958.GA32376@linux.intel.com> (raw)
In-Reply-To: <1463070560-1979-3-git-send-email-jack@suse.cz>

On Thu, May 12, 2016 at 06:29:15PM +0200, Jan Kara wrote:
> Currently the handling of huge pages for DAX is racy. For example the
> following can happen:
> 
> CPU0 (THP write fault)			CPU1 (normal read fault)
> 
> __dax_pmd_fault()			__dax_fault()
>   get_block(inode, block, &bh, 0) -> not mapped
> 					get_block(inode, block, &bh, 0)
> 					  -> not mapped
>   if (!buffer_mapped(&bh) && write)
>     get_block(inode, block, &bh, 1) -> allocates blocks
>   truncate_pagecache_range(inode, lstart, lend);
> 					dax_load_hole();
> 
> This results in data corruption since process on CPU1 won't see changes
> into the file done by CPU0.
> 
> The race can happen even if two normal faults race however with THP the
> situation is even worse because the two faults don't operate on the same
> entries in the radix tree and we want to use these entries for
> serialization. So make THP support in DAX code depend on CONFIG_BROKEN
> for now.
> 
> Signed-off-by: Jan Kara <jack@suse.cz>

Reviewed-by: Ross Zwisler <ross.zwisler@linux.intel.com>

WARNING: multiple messages have this Message-ID (diff)
From: Ross Zwisler <ross.zwisler@linux.intel.com>
To: Jan Kara <jack@suse.cz>
Cc: Ted Tso <tytso@mit.edu>,
	linux-nvdimm@lists.01.org, linux-fsdevel@vger.kernel.org,
	linux-ext4@vger.kernel.org
Subject: Re: [PATCH 2/7] dax: Make huge page handling depend of CONFIG_BROKEN
Date: Thu, 12 May 2016 12:59:58 -0600	[thread overview]
Message-ID: <20160512185958.GA32376@linux.intel.com> (raw)
In-Reply-To: <1463070560-1979-3-git-send-email-jack@suse.cz>

On Thu, May 12, 2016 at 06:29:15PM +0200, Jan Kara wrote:
> Currently the handling of huge pages for DAX is racy. For example the
> following can happen:
> 
> CPU0 (THP write fault)			CPU1 (normal read fault)
> 
> __dax_pmd_fault()			__dax_fault()
>   get_block(inode, block, &bh, 0) -> not mapped
> 					get_block(inode, block, &bh, 0)
> 					  -> not mapped
>   if (!buffer_mapped(&bh) && write)
>     get_block(inode, block, &bh, 1) -> allocates blocks
>   truncate_pagecache_range(inode, lstart, lend);
> 					dax_load_hole();
> 
> This results in data corruption since process on CPU1 won't see changes
> into the file done by CPU0.
> 
> The race can happen even if two normal faults race however with THP the
> situation is even worse because the two faults don't operate on the same
> entries in the radix tree and we want to use these entries for
> serialization. So make THP support in DAX code depend on CONFIG_BROKEN
> for now.
> 
> Signed-off-by: Jan Kara <jack@suse.cz>

Reviewed-by: Ross Zwisler <ross.zwisler@linux.intel.com>
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  reply	other threads:[~2016-05-12 18:59 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-05-12 16:29 [PATCH 0/7 v4] DAX page fault locking Jan Kara
2016-05-12 16:29 ` Jan Kara
2016-05-12 16:29 ` [PATCH 1/7] dax: Fix condition for filling of PMD holes Jan Kara
2016-05-12 16:29   ` Jan Kara
2016-05-12 19:03   ` Ross Zwisler
2016-05-12 19:03     ` Ross Zwisler
2016-05-12 16:29 ` [PATCH 2/7] dax: Make huge page handling depend of CONFIG_BROKEN Jan Kara
2016-05-12 16:29   ` Jan Kara
2016-05-12 18:59   ` Ross Zwisler [this message]
2016-05-12 18:59     ` Ross Zwisler
2016-05-12 16:29 ` [PATCH 3/7] dax: Define DAX lock bit for radix tree exceptional entry Jan Kara
2016-05-12 16:29   ` Jan Kara
2016-05-12 16:29 ` [PATCH 4/7] dax: Allow DAX code to replace exceptional entries Jan Kara
2016-05-12 16:29   ` Jan Kara
2016-05-12 16:29 ` [PATCH 5/7] dax: New fault locking Jan Kara
2016-05-12 16:29   ` Jan Kara
2016-05-12 19:36   ` Ross Zwisler
2016-05-12 19:36     ` Ross Zwisler
2016-05-12 19:36     ` Ross Zwisler
2016-05-19  9:27     ` Jan Kara
2016-05-19  9:27       ` Jan Kara
2016-05-19  9:27       ` Jan Kara
2016-05-12 16:29 ` [PATCH 6/7] dax: Use radix tree entry lock to protect cow faults Jan Kara
2016-05-12 16:29   ` Jan Kara
2016-05-12 16:29 ` [PATCH 7/7] dax: Remove i_mmap_lock protection Jan Kara
2016-05-12 16:29   ` Jan Kara
2016-05-12 16:29   ` Jan Kara

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