From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg0-f72.google.com (mail-pg0-f72.google.com [74.125.83.72]) by kanga.kvack.org (Postfix) with ESMTP id B90806B0038 for ; Mon, 1 May 2017 12:54:55 -0400 (EDT) Received: by mail-pg0-f72.google.com with SMTP id p2so45922880pge.7 for ; Mon, 01 May 2017 09:54:55 -0700 (PDT) Received: from mga01.intel.com (mga01.intel.com. [192.55.52.88]) by mx.google.com with ESMTPS id v71si3303132pgd.186.2017.05.01.09.54.54 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 01 May 2017 09:54:54 -0700 (PDT) Date: Mon, 1 May 2017 10:54:51 -0600 From: Ross Zwisler Subject: Re: [PATCH 1/2] dax: prevent invalidation of mapped DAX entries Message-ID: <20170501165451.GB14837@linux.intel.com> References: <20170420191446.GA21694@linux.intel.com> <20170421034437.4359-1-ross.zwisler@linux.intel.com> <20170425101041.GG2793@quack2.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170425101041.GG2793@quack2.suse.cz> Sender: owner-linux-mm@kvack.org List-ID: To: Jan Kara Cc: Ross Zwisler , Andrew Morton , linux-kernel@vger.kernel.org, Alexander Viro , Alexey Kuznetsov , Andrey Ryabinin , Anna Schumaker , Christoph Hellwig , Dan Williams , "Darrick J. Wong" , Eric Van Hensbergen , Jens Axboe , Johannes Weiner , Konrad Rzeszutek Wilk , Latchesar Ionkov , linux-cifs@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-nfs@vger.kernel.org, linux-nvdimm@lists.01.org, Matthew Wilcox , Ron Minnich , samba-technical@lists.samba.org, Steve French , Trond Myklebust , v9fs-developer@lists.sourceforge.net On Tue, Apr 25, 2017 at 12:10:41PM +0200, Jan Kara wrote: > On Thu 20-04-17 21:44:36, Ross Zwisler wrote: > > dax_invalidate_mapping_entry() currently removes DAX exceptional entries > > only if they are clean and unlocked. This is done via: > > > > invalidate_mapping_pages() > > invalidate_exceptional_entry() > > dax_invalidate_mapping_entry() > > > > However, for page cache pages removed in invalidate_mapping_pages() there > > is an additional criteria which is that the page must not be mapped. This > > is noted in the comments above invalidate_mapping_pages() and is checked in > > invalidate_inode_page(). > > > > For DAX entries this means that we can can end up in a situation where a > > DAX exceptional entry, either a huge zero page or a regular DAX entry, > > could end up mapped but without an associated radix tree entry. This is > > inconsistent with the rest of the DAX code and with what happens in the > > page cache case. > > > > We aren't able to unmap the DAX exceptional entry because according to its > > comments invalidate_mapping_pages() isn't allowed to block, and > > unmap_mapping_range() takes a write lock on the mapping->i_mmap_rwsem. > > > > Since we essentially never have unmapped DAX entries to evict from the > > radix tree, just remove dax_invalidate_mapping_entry(). > > > > Signed-off-by: Ross Zwisler > > Fixes: c6dcf52c23d2 ("mm: Invalidate DAX radix tree entries only if appropriate") > > Reported-by: Jan Kara > > Cc: [4.10+] > > Just as a side note - we wouldn't really have to unmap the mapping range > covered by the DAX exceptional entry. It would be enough to find out > whether such range is mapped and bail out in that case. But that would > still be pretty expensive for DAX - we'd have to do rmap walk similar as in > dax_mapping_entry_mkclean() and IMHO it is not worth it. So I agree with > what you did. You can add: > > Reviewed-by: Jan Kara Yep, that makes sense. Thanks for the review. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org