From: "Jan H. Schönherr" <jschoenh@amazon.de>
To: Matthew Wilcox <willy@infradead.org>
Cc: Matthew Wilcox <mawilcox@microsoft.com>,
Ross Zwisler <ross.zwisler@linux.intel.com>,
linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH] dax: Release PMD lock even when there is no PMD support in DAX
Date: Thu, 18 Jan 2018 15:22:58 +0100 [thread overview]
Message-ID: <5c50be9f-0ade-41ae-e137-0171ed1ef924@amazon.de> (raw)
In-Reply-To: <20180118140739.GA28322@bombadil.infradead.org>
On 01/18/2018 03:07 PM, Matthew Wilcox wrote:
> On Thu, Jan 18, 2018 at 02:38:39PM +0100, Jan H. Schönherr wrote:
>> The function follow_pte_pmd() can theoretically return after having
>> acquired a PMD lock, even when DAX was not compiled with
>> CONFIG_FS_DAX_PMD.
>
> I don't think it can. How would a PMD entry get into a DAX VMA if we
> compiled the kernel without CONFIG_FS_DAX_PMD?
>
Maybe it can not in happy cases. But the PMD parts in follow_pte_pmd() are compiled in
unconditionally. So, if there's an issue elsewhere, and for some weird reason we get a PMD entry
in the page table, it would screw the lock balance.
I haven't run into an actual issue with this, it's just supposed to be defensive.
Regards
Jan
next prev parent reply other threads:[~2018-01-18 14:23 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-18 13:38 [PATCH] dax: Release PMD lock even when there is no PMD support in DAX Jan H. Schönherr
2018-01-18 14:07 ` Matthew Wilcox
2018-01-18 14:22 ` Matthew Wilcox
2018-01-18 14:27 ` Jan H. Schönherr
2018-01-18 14:35 ` Jan H. Schönherr
2018-01-18 14:22 ` Jan H. Schönherr [this message]
2018-01-18 16:20 ` Ross Zwisler
2018-01-25 16:34 ` Ross Zwisler
2018-01-25 21:29 ` Jan H. Schönherr
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