From: Matthew Wilcox <willy@infradead.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Muchun Song <songmuchun@bytedance.com>,
jgg@ziepe.ca, jhubbard@nvidia.com, william.kucharski@oracle.com,
dan.j.williams@intel.com, jack@suse.cz, linux-mm@kvack.org,
linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
nvdimm@lists.linux.dev, stable@vger.kernel.org
Subject: Re: [PATCH v2] mm: fix missing wake-up event for FSDAX pages
Date: Wed, 6 Jul 2022 00:38:41 +0100 [thread overview]
Message-ID: <YsTLgQ45ESpsNEGV@casper.infradead.org> (raw)
In-Reply-To: <20220705141819.804eb972d43be3434dc70192@linux-foundation.org>
On Tue, Jul 05, 2022 at 02:18:19PM -0700, Andrew Morton wrote:
> On Tue, 5 Jul 2022 20:35:32 +0800 Muchun Song <songmuchun@bytedance.com> wrote:
>
> > FSDAX page refcounts are 1-based, rather than 0-based: if refcount is
> > 1, then the page is freed. The FSDAX pages can be pinned through GUP,
> > then they will be unpinned via unpin_user_page() using a folio variant
> > to put the page, however, folio variants did not consider this special
> > case, the result will be to miss a wakeup event (like the user of
> > __fuse_dax_break_layouts()). Since FSDAX pages are only possible get
> > by GUP users, so fix GUP instead of folio_put() to lower overhead.
> >
>
> What are the user visible runtime effects of this bug?
"missing wake up event" seems pretty obvious to me? Something goes to
sleep waiting for a page to become unused, and is never woken.
next prev parent reply other threads:[~2022-07-05 23:39 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-07-05 12:35 Muchun Song
2022-07-05 21:18 ` Andrew Morton
2022-07-05 23:38 ` Matthew Wilcox [this message]
2022-07-05 23:47 ` Andrew Morton
2022-07-06 2:47 ` Muchun Song
2022-07-06 3:00 ` Andrew Morton
2022-07-06 3:11 ` Muchun Song
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