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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>,
	Matthew Wilcox <mawilcox@microsoft.com>,
	Ross Zwisler <ross.zwisler@linux.intel.com>,
	linux-mm@kvack.org, linux-fsdevel@vger.kernel.org,
	tony.luck@intel.com
Subject: Re: [PATCH 06/11] filesystem-dax: perform __dax_invalidate_mapping_entry() under the page lock
Date: Wed, 23 May 2018 11:35:37 +0200	[thread overview]
Message-ID: <20180523093537.duw6jlglcx7fnutw@quack2.suse.cz> (raw)
In-Reply-To: <152700000355.24093.14726378287214432782.stgit@dwillia2-desk3.amr.corp.intel.com>

On Tue 22-05-18 07:40:03, Dan Williams wrote:
> Hold the page lock while invalidating mapping entries to prevent races
> between rmap using the address_space and the filesystem freeing the
> address_space.
> 
> This is more complicated than the simple description implies because
> dev_pagemap pages that fsdax uses do not have any concept of page size.
> Size information is stored in the radix and can only be safely read
> while holding the xa_lock. Since lock_page() can not be taken while
> holding xa_lock, drop xa_lock and speculatively lock all the associated
> pages. Once all the pages are locked re-take the xa_lock and revalidate
> that the radix entry did not change.
> 
> Cc: Jan Kara <jack@suse.cz>
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Matthew Wilcox <mawilcox@microsoft.com>
> Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>

IMO this is too ugly to live. The combination of entry locks in the radix
tree and page locks is just too big mess. And from a quick look I don't see
a reason why we could not use entry locks to protect rmap code as well -
when you have PFN for which you need to walk rmap, you can grab
rcu_read_lock(), then you can safely look at page->mapping, grab xa_lock,
verify the radix tree points where it should and grab entry lock. I agree
it's a bit complicated but for memory failure I think it is fine.

Or we could talk about switching everything to page locks instead of entry
locks but that isn't trivial either as we need something to serialized page
faults on even before we go into the filesystem and allocate blocks for the
fault...
								Honza

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

  reply	other threads:[~2018-05-23  9:35 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-22 14:39 [PATCH 00/11] mm: Teach memory_failure() about ZONE_DEVICE pages Dan Williams
2018-05-22 14:39 ` [PATCH 01/11] device-dax: convert to vmf_insert_mixed and vm_fault_t Dan Williams
2018-05-22 14:39 ` [PATCH 02/11] device-dax: cleanup vm_fault de-reference chains Dan Williams
2018-05-22 14:39 ` [PATCH 03/11] device-dax: enable page_mapping() Dan Williams
2018-05-23  9:03   ` Jan Kara
2018-05-30 19:54   ` kbuild test robot
2018-05-22 14:39 ` [PATCH 04/11] device-dax: set page->index Dan Williams
2018-05-22 14:39 ` [PATCH 05/11] filesystem-dax: " Dan Williams
2018-05-23  8:40   ` Jan Kara
2018-05-30  1:38     ` Dan Williams
2018-05-30  8:13       ` Jan Kara
2018-05-30 23:21         ` Dan Williams
2018-05-31 10:08           ` Jan Kara
2018-05-31 21:49             ` Dan Williams
2018-05-22 14:40 ` [PATCH 06/11] filesystem-dax: perform __dax_invalidate_mapping_entry() under the page lock Dan Williams
2018-05-23  9:35   ` Jan Kara [this message]
2018-05-23 13:50     ` Dan Williams
2018-05-22 14:40 ` [PATCH 07/11] mm, madvise_inject_error: fix page count leak Dan Williams
2018-05-23  4:19   ` Naoya Horiguchi
2018-05-24 20:55     ` Dan Williams
2018-05-22 14:40 ` [PATCH 08/11] x86, memory_failure: introduce {set, clear}_mce_nospec() Dan Williams
2018-05-22 14:40 ` [PATCH 09/11] mm, memory_failure: pass page size to kill_proc() Dan Williams
2018-05-23  6:41   ` Naoya Horiguchi
2018-05-22 14:40 ` [PATCH 10/11] mm, memory_failure: teach memory_failure() about dev_pagemap pages Dan Williams
2018-05-23  6:48   ` Naoya Horiguchi
2018-05-22 14:40 ` [PATCH 11/11] libnvdimm, pmem: restore page attributes when clearing errors Dan Williams

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