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From: Ross Zwisler <ross.zwisler@linux.intel.com>
To: Dave Hansen <dave.hansen@intel.com>
Cc: Jan Kara <jack@suse.cz>,
	Andrew Morton <akpm@linux-foundation.org>,
	"Darrick J. Wong" <darrick.wong@oracle.com>,
	Matthew Wilcox <mawilcox@microsoft.com>,
	linux-kernel@vger.kernel.org, stable@vger.kernel.org,
	linux-mm@kvack.org, Alexander Viro <viro@zeniv.linux.org.uk>,
	linux-fsdevel@vger.kernel.org, Eryu Guan <eguan@redhat.com>,
	Christoph Hellwig <hch@lst.de>,
	"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
	linux-nvdimm@lists.01.org
Subject: Re: [PATCH 1/2] mm: avoid spurious 'bad pmd' warning messages
Date: Wed, 17 May 2017 12:23:09 -0600	[thread overview]
Message-ID: <20170517182309.GA30704@linux.intel.com> (raw)
In-Reply-To: <9c45c769-2f5e-9327-c39e-1df7744fa633@intel.com>

On Wed, May 17, 2017 at 10:33:58AM -0700, Dave Hansen wrote:
> On 05/17/2017 10:16 AM, Ross Zwisler wrote:
> > @@ -3061,7 +3061,7 @@ static int pte_alloc_one_map(struct vm_fault *vmf)
> >  	 * through an atomic read in C, which is what pmd_trans_unstable()
> >  	 * provides.
> >  	 */
> > -	if (pmd_trans_unstable(vmf->pmd) || pmd_devmap(*vmf->pmd))
> > +	if (pmd_devmap(*vmf->pmd) || pmd_trans_unstable(vmf->pmd))
> >  		return VM_FAULT_NOPAGE;
> 
> I'm worried we are very unlikely to get this right in the future.  It's
> totally not obvious what the ordering requirement is here.
> 
> Could we move pmd_devmap() and pmd_trans_unstable() into a helper that
> gets the ordering right and also spells out the ordering requirement?

Sure, I'll fix this for v2.

Thanks for the review.
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WARNING: multiple messages have this Message-ID (diff)
From: Ross Zwisler <ross.zwisler@linux.intel.com>
To: Dave Hansen <dave.hansen@intel.com>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	linux-kernel@vger.kernel.org,
	"Darrick J. Wong" <darrick.wong@oracle.com>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Christoph Hellwig <hch@lst.de>,
	Dan Williams <dan.j.williams@intel.com>, Jan Kara <jack@suse.cz>,
	Matthew Wilcox <mawilcox@microsoft.com>,
	linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
	linux-nvdimm@lists.01.org,
	"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
	Pawel Lebioda <pawel.lebioda@intel.com>,
	Dave Jiang <dave.jiang@intel.com>, Xiong Zhou <xzhou@redhat.com>,
	Eryu Guan <eguan@redhat.com>,
	stable@vger.kernel.org
Subject: Re: [PATCH 1/2] mm: avoid spurious 'bad pmd' warning messages
Date: Wed, 17 May 2017 12:23:09 -0600	[thread overview]
Message-ID: <20170517182309.GA30704@linux.intel.com> (raw)
In-Reply-To: <9c45c769-2f5e-9327-c39e-1df7744fa633@intel.com>

On Wed, May 17, 2017 at 10:33:58AM -0700, Dave Hansen wrote:
> On 05/17/2017 10:16 AM, Ross Zwisler wrote:
> > @@ -3061,7 +3061,7 @@ static int pte_alloc_one_map(struct vm_fault *vmf)
> >  	 * through an atomic read in C, which is what pmd_trans_unstable()
> >  	 * provides.
> >  	 */
> > -	if (pmd_trans_unstable(vmf->pmd) || pmd_devmap(*vmf->pmd))
> > +	if (pmd_devmap(*vmf->pmd) || pmd_trans_unstable(vmf->pmd))
> >  		return VM_FAULT_NOPAGE;
> 
> I'm worried we are very unlikely to get this right in the future.  It's
> totally not obvious what the ordering requirement is here.
> 
> Could we move pmd_devmap() and pmd_trans_unstable() into a helper that
> gets the ordering right and also spells out the ordering requirement?

Sure, I'll fix this for v2.

Thanks for the review.

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WARNING: multiple messages have this Message-ID (diff)
From: Ross Zwisler <ross.zwisler@linux.intel.com>
To: Dave Hansen <dave.hansen@intel.com>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	linux-kernel@vger.kernel.org,
	"Darrick J. Wong" <darrick.wong@oracle.com>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Christoph Hellwig <hch@lst.de>,
	Dan Williams <dan.j.williams@intel.com>, Jan Kara <jack@suse.cz>,
	Matthew Wilcox <mawilcox@microsoft.com>,
	linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
	linux-nvdimm@ml01.01.org,
	"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
	Pawel Lebioda <pawel.lebioda@intel.com>,
	Dave Jiang <dave.jiang@intel.com>, Xiong Zhou <xzhou@redhat.com>,
	Eryu Guan <eguan@redhat.com>,
	stable@vger.kernel.org
Subject: Re: [PATCH 1/2] mm: avoid spurious 'bad pmd' warning messages
Date: Wed, 17 May 2017 12:23:09 -0600	[thread overview]
Message-ID: <20170517182309.GA30704@linux.intel.com> (raw)
In-Reply-To: <9c45c769-2f5e-9327-c39e-1df7744fa633@intel.com>

On Wed, May 17, 2017 at 10:33:58AM -0700, Dave Hansen wrote:
> On 05/17/2017 10:16 AM, Ross Zwisler wrote:
> > @@ -3061,7 +3061,7 @@ static int pte_alloc_one_map(struct vm_fault *vmf)
> >  	 * through an atomic read in C, which is what pmd_trans_unstable()
> >  	 * provides.
> >  	 */
> > -	if (pmd_trans_unstable(vmf->pmd) || pmd_devmap(*vmf->pmd))
> > +	if (pmd_devmap(*vmf->pmd) || pmd_trans_unstable(vmf->pmd))
> >  		return VM_FAULT_NOPAGE;
> 
> I'm worried we are very unlikely to get this right in the future.  It's
> totally not obvious what the ordering requirement is here.
> 
> Could we move pmd_devmap() and pmd_trans_unstable() into a helper that
> gets the ordering right and also spells out the ordering requirement?

Sure, I'll fix this for v2.

Thanks for the review.

  reply	other threads:[~2017-05-17 18:23 UTC|newest]

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-05-17 17:16 [PATCH 1/2] mm: avoid spurious 'bad pmd' warning messages Ross Zwisler
2017-05-17 17:16 ` Ross Zwisler
2017-05-17 17:16 ` Ross Zwisler
2017-05-17 17:16 ` [PATCH 2/2] dax: Fix race between colliding PMD & PTE entries Ross Zwisler
2017-05-17 17:16   ` Ross Zwisler
2017-05-17 17:16   ` Ross Zwisler
2017-05-17 17:17   ` [PATCH] generic: add regression test for DAX PTE/PMD races Ross Zwisler
2017-05-17 17:17     ` Ross Zwisler
2017-05-18  7:50   ` [PATCH 2/2] dax: Fix race between colliding PMD & PTE entries Jan Kara
2017-05-18  7:50     ` Jan Kara
2017-05-18  7:50     ` Jan Kara
2017-05-18 21:29     ` Ross Zwisler
2017-05-18 21:29       ` Ross Zwisler
2017-05-18 21:29       ` Ross Zwisler
2017-05-22 14:37       ` Jan Kara
2017-05-22 14:37         ` Jan Kara
2017-05-22 14:37         ` Jan Kara
2017-05-22 19:44         ` Ross Zwisler
2017-05-22 19:44           ` Ross Zwisler
2017-05-22 14:44   ` Jan Kara
2017-05-22 14:44     ` Jan Kara
2017-05-22 14:44     ` Jan Kara
2017-05-22 19:43     ` Ross Zwisler
2017-05-22 19:43       ` Ross Zwisler
2017-05-22 19:43       ` Ross Zwisler
2017-05-17 17:33 ` [PATCH 1/2] mm: avoid spurious 'bad pmd' warning messages Dave Hansen
2017-05-17 17:33   ` Dave Hansen
2017-05-17 17:33   ` Dave Hansen
2017-05-17 18:23   ` Ross Zwisler [this message]
2017-05-17 18:23     ` Ross Zwisler
2017-05-17 18:23     ` Ross Zwisler
2017-05-22 14:40 ` Jan Kara
2017-05-22 14:40   ` Jan Kara
2017-05-22 14:40   ` Jan Kara

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