From mboxrd@z Thu Jan 1 00:00:00 1970 From: jack@suse.cz (Jan Kara) Date: Tue, 9 Apr 2013 23:11:28 +0200 Subject: [PATCH v3] [RESEND] mm: Make snapshotting pages for stable writes a per-bio operation In-Reply-To: <20130409140432.cd69f999302a02caf73788fc@linux-foundation.org> References: <20130409180617.GB8907@blackbox.djwong.org> <20130409140432.cd69f999302a02caf73788fc@linux-foundation.org> Message-ID: <20130409211128.GD15214@quack.suse.cz> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Tue 09-04-13 14:04:32, Andrew Morton wrote: > On Tue, 9 Apr 2013 11:06:17 -0700 "Darrick J. Wong" wrote: > > > + * Here we write back pagecache data that may be mmaped. Since > > + * we cannot afford to clean the page and set PageWriteback > > + * here due to lock ordering (page lock ranks above transaction > > + * start), the data can change while IO is in flight. Tell the > > + * block layer it should bounce the bio pages if stable data > > + * during write is required. > > I think there are already ab/ba deadlocks between lock_page() and > journal_start(). iirc one path was write(), I forget which was the > other path. This was 10+ years ago and nobody else noticed and I > didn't know how to fix it so I didn't tell anyone ;) Hum, I don't think they are there anymore ;) > It would be neat to be able to hook things like journal_start() into > lockdep but I don't think that lockdep has easy provision for wiring > oddball things into its mechanisms. Actually if you look at fs/jbd/transaction.c:start_this_handle(), you will notice that it is wired into lockdep (the lock_map_acquire() call there). And it works since I've seen quite some reports from it ;) Honza -- Jan Kara SUSE Labs, CR