From: Ross Zwisler <ross.zwisler@linux.intel.com>
To: "Wilcox, Matthew R" <matthew.r.wilcox@intel.com>
Cc: Jared Hulbert <jaredeh@gmail.com>,
"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
"ross.zwisler@linux.intel.com" <ross.zwisler@linux.intel.com>
Subject: Re: bug in COW no page fault?
Date: Mon, 1 Feb 2016 14:12:24 -0700 [thread overview]
Message-ID: <20160201211224.GA21755@linux.intel.com> (raw)
In-Reply-To: <100D68C7BA14664A8938383216E40DE04217F8A5@FMSMSX114.amr.corp.intel.com>
On Sat, Jan 30, 2016 at 05:47:18AM +0000, Wilcox, Matthew R wrote:
> I remembered that Ross had a similar question, so it must be hard to understand. How does this comment work for both of you?
>
> + /*
> + * A truncate must remove COWs of pages that are removed
> + * from the file. If we have a struct page, the normal
> + * page lock mechanism prevents truncate from missing the
> + * COWed page. If not, the i_mmap_lock can provide the
> + * same guarantee. It is dropped by the caller after the
> + * page is safely in the page tables.
> + */
Yep, this makes sense. It may be worthwhile to explicitly say "It is dropped
by do_cow_fault() after the page is safely in the page tables." so the less
experienced among us (me) can easily find the match to the i_mmap_lock_read().
prev parent reply other threads:[~2016-02-01 21:12 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-29 21:38 DAX: bug in COW no page fault? Jared Hulbert
2016-01-29 21:53 ` Wilcox, Matthew R
2016-01-29 22:12 ` Jared Hulbert
2016-01-29 22:36 ` Wilcox, Matthew R
2016-01-29 23:16 ` Jared Hulbert
2016-01-30 5:47 ` Wilcox, Matthew R
2016-01-30 6:34 ` Jared Hulbert
2016-02-01 21:12 ` Ross Zwisler [this message]
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