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From: Jan Kara <jack@suse.cz>
To: Dan Williams <dan.j.williams@intel.com>
Cc: linux-nvdimm@lists.01.org, "Jan Kara" <jack@suse.cz>,
	"Christoph Hellwig" <hch@lst.de>,
	"Jérôme Glisse" <jglisse@redhat.com>,
	"Matthew Wilcox" <mawilcox@microsoft.com>,
	"Naoya Horiguchi" <n-horiguchi@ah.jp.nec.com>,
	"Ross Zwisler" <ross.zwisler@linux.intel.com>,
	linux-mm@kvack.org, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH v3 11/12] mm, memory_failure: Teach memory_failure() about dev_pagemap pages
Date: Thu, 7 Jun 2018 18:30:36 +0200	[thread overview]
Message-ID: <20180607163036.o7vmi6onrsexphrk@quack2.suse.cz> (raw)
In-Reply-To: <152815395775.39010.9355109660470832490.stgit@dwillia2-desk3.amr.corp.intel.com>

On Mon 04-06-18 16:12:37, Dan Williams wrote:
>     mce: Uncorrected hardware memory error in user-access at af34214200
>     {1}[Hardware Error]: It has been corrected by h/w and requires no further action
>     mce: [Hardware Error]: Machine check events logged
>     {1}[Hardware Error]: event severity: corrected
>     Memory failure: 0xaf34214: reserved kernel page still referenced by 1 users
>     [..]
>     Memory failure: 0xaf34214: recovery action for reserved kernel page: Failed
>     mce: Memory error not recovered
> 
> In contrast to typical memory, dev_pagemap pages may be dax mapped. With
> dax there is no possibility to map in another page dynamically since dax
> establishes 1:1 physical address to file offset associations. Also
> dev_pagemap pages associated with NVDIMM / persistent memory devices can
> internal remap/repair addresses with poison. While memory_failure()
> assumes that it can discard typical poisoned pages and keep them
> unmapped indefinitely, dev_pagemap pages may be returned to service
> after the error is cleared.
> 
> Teach memory_failure() to detect and handle MEMORY_DEVICE_HOST
> dev_pagemap pages that have poison consumed by userspace. Mark the
> memory as UC instead of unmapping it completely to allow ongoing access
> via the device driver (nd_pmem). Later, nd_pmem will grow support for
> marking the page back to WB when the error is cleared.

...

> +static int memory_failure_dev_pagemap(unsigned long pfn, int flags,
> +		struct dev_pagemap *pgmap)
> +{
> +	struct page *page = pfn_to_page(pfn);
> +	const bool unmap_success = true;
> +	struct address_space *mapping;
> +	unsigned long size;
> +	LIST_HEAD(tokill);
> +	int rc = -EBUSY;
> +	loff_t start;
> +
> +	/*
> +	 * Prevent the inode from being freed while we are interrogating
> +	 * the address_space, typically this would be handled by
> +	 * lock_page(), but dax pages do not use the page lock.
> +	 */
> +	rcu_read_lock();
> +	mapping = page->mapping;
> +	if (!mapping) {
> +		rcu_read_unlock();
> +		goto out;
> +	}
> +	if (!igrab(mapping->host)) {
> +		mapping = NULL;
> +		rcu_read_unlock();
> +		goto out;
> +	}
> +	rcu_read_unlock();

Why don't you use radix tree entry lock here instead? That is a direct
replacement of the page lock and you don't have to play games with pinning
the inode and verifying the mapping afterwards.

> +out:
> +	if (mapping)
> +		iput(mapping->host);

BTW, this would have to be prepared to do full inode deletion which I'm not
quite sure is safe from this context.

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

  parent reply	other threads:[~2018-06-07 16:30 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-06-04 23:11 [PATCH v3 00/12] mm: Teach memory_failure() about ZONE_DEVICE pages Dan Williams
2018-06-04 23:11 ` [PATCH v3 01/12] device-dax: Convert to vmf_insert_mixed and vm_fault_t Dan Williams
2018-06-04 23:11 ` [PATCH v3 02/12] device-dax: Cleanup vm_fault de-reference chains Dan Williams
2018-06-04 23:11 ` [PATCH v3 03/12] device-dax: Enable page_mapping() Dan Williams
2018-06-07 15:39   ` Jan Kara
2018-06-04 23:12 ` [PATCH v3 04/12] device-dax: Set page->index Dan Williams
2018-06-07 15:50   ` Jan Kara
2018-06-04 23:12 ` [PATCH v3 05/12] filesystem-dax: " Dan Williams
2018-06-07 16:02   ` Jan Kara
2018-06-04 23:12 ` [PATCH v3 06/12] mm, madvise_inject_error: Let memory_failure() optionally take a page reference Dan Williams
2018-06-04 23:12 ` [PATCH v3 07/12] x86/mm/pat: Prepare {reserve, free}_memtype() for "decoy" addresses Dan Williams
2018-06-04 23:12 ` [PATCH v3 08/12] x86/memory_failure: Introduce {set, clear}_mce_nospec() Dan Williams
2018-06-07  4:42   ` Dan Williams
2018-06-07 17:02     ` Luck, Tony
2018-06-04 23:12 ` [PATCH v3 09/12] mm, memory_failure: Pass page size to kill_proc() Dan Williams
2018-06-04 23:12 ` [PATCH v3 10/12] mm, memory_failure: Fix page->mapping assumptions relative to the page lock Dan Williams
2018-06-04 23:12 ` [PATCH v3 11/12] mm, memory_failure: Teach memory_failure() about dev_pagemap pages Dan Williams
2018-06-07  4:22   ` Dan Williams
2018-06-07 16:30   ` Jan Kara [this message]
2018-06-07 16:45     ` Dan Williams
2018-06-04 23:12 ` [PATCH v3 12/12] libnvdimm, pmem: Restore page attributes when clearing errors Dan Williams

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