From: Jerome Glisse <jglisse@redhat.com>
To: Hugh Dickins <hughd@google.com>
Cc: linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
Huang Ying <ying.huang@intel.com>,
linux-kernel@vger.kernel.org,
Steven Capper <steve.capper@linaro.org>,
Catalin Marinas <catalin.marinas@arm.com>,
Rabin Vincent <rabinv@axis.com>,
linux-arm-kernel@lists.infradead.org,
rmk+kernel@arm.linux.org.uk, Guo Ren <guoren@kernel.org>,
linux-mips@vger.kernel.org, Ralf Baechle <ralf@linux-mips.org>,
Paul Burton <paulburton@kernel.org>,
James Hogan <jhogan@kernel.org>, Ley Foon Tan <lftan@altera.com>,
nios2-dev@lists.rocketboards.org, linux-parisc@vger.kernel.org,
Helge Deller <deller@gmx.de>,
"James E.J. Bottomley" <James.Bottomley@hansenpartnership.com>,
Yoshinori Sato <ysato@users.sourceforge.jp>,
Rich Felker <dalias@libc.org>,
linux-sh@vger.kernel.org, "David S. Miller" <davem@davemloft.net>,
sparclinux@vger.kernel.org, Guan Xuetao <gxt@pku.edu.cn>,
linux-xtensa@linux-xtensa.org, Max Filippov <jcmvbkbc@gmail.com>,
Chris Zankel <chris@zankel.net>
Subject: Re: Cache flush issue with page_mapping_file() and swap back shmem page ?
Date: Thu, 28 May 2020 07:20:25 -0400 [thread overview]
Message-ID: <20200528112025.GA10175@redhat.com> (raw)
In-Reply-To: <alpine.LSU.2.11.2005272021220.3857@eggly.anvils>
On Wed, May 27, 2020 at 08:46:22PM -0700, Hugh Dickins wrote:
> Hi Jerome,
>
> On Wed, 27 May 2020, Jerome Glisse wrote:
> > So any arch code which uses page_mapping_file() might get the wrong
> > answer, this function will return NULL for a swap backed page which
> > can be a shmem pages. But shmem pages can still be shared among
> > multiple process (and possibly at different virtual addresses if
> > mremap was use).
> >
> > Attached is a patch that changes page_mapping_file() to return the
> > shmem mapping for swap backed shmem page. I have not tested it (no
> > way for me to test all those architecture) and i spotted this while
> > working on something else. So i hope someone can take a closer look.
>
> I'm certainly no expert on flush_dcache_page() and friends, but I'd
> be very surprised if such a problem exists, yet has gone unnoticed
> for so long. page_mapping_file() itself is fairly new, added when
> a risk of crashing on a race with swapoff came in: but the previous
> use of page_mapping() would have suffered equally if there were such
> a cache flushinhg problem here.
>
> And I'm afraid your patch won't do anything to help if there is a
> problem: very soon after shmem calls add_to_swap_cache(), it calls
> shmem_delete_from_page_cache(), which sets page->mapping to NULL.
>
> But I can assure you that a shmem page (unlike an anon page) is never
> put into swap cache while it is mapped into userspace, and never
> mapped into userspace while it is still in swap cache: does that help?
>
You are right i missed/forgot the part where shmem is never swapcache
and mapped at the same time, thus page_mapping_file() can return NULL
for those as they can no longer have alias mapping.
Thank you Hugh
Jérôme
WARNING: multiple messages have this Message-ID (diff)
From: Jerome Glisse <jglisse@redhat.com>
To: Hugh Dickins <hughd@google.com>
Cc: Rich Felker <dalias@libc.org>,
linux-sh@vger.kernel.org,
Catalin Marinas <catalin.marinas@arm.com>,
linux-mips@vger.kernel.org,
"James E.J. Bottomley" <James.Bottomley@hansenpartnership.com>,
linux-mm@kvack.org, Guo Ren <guoren@kernel.org>,
sparclinux@vger.kernel.org, Paul Burton <paulburton@kernel.org>,
Helge Deller <deller@gmx.de>, Huang Ying <ying.huang@intel.com>,
James Hogan <jhogan@kernel.org>,
rmk+kernel@arm.linux.org.uk, linux-xtensa@linux-xtensa.org,
Steven Capper <steve.capper@linaro.org>,
Rabin Vincent <rabinv@axis.com>, Ley Foon Tan <lftan@altera.com>,
Guan Xuetao <gxt@pku.edu.cn>,
linux-arm-kernel@lists.infradead.org,
Chris Zankel <chris@zankel.net>,
Yoshinori Sato <ysato@users.sourceforge.jp>,
linux-parisc@vger.kernel.org, Max Filippov <jcmvbkbc@gmail.com>,
linux-kernel@vger.kernel.org, Ralf Baechle <ralf@linux-mips.org>,
nios2-dev@lists.rocketboards.org,
Andrew Morton <akpm@linux-foundation.org>,
"David S. Miller" <davem@davemloft.net>
Subject: Re: Cache flush issue with page_mapping_file() and swap back shmem page ?
Date: Thu, 28 May 2020 11:20:25 +0000 [thread overview]
Message-ID: <20200528112025.GA10175@redhat.com> (raw)
In-Reply-To: <alpine.LSU.2.11.2005272021220.3857@eggly.anvils>
On Wed, May 27, 2020 at 08:46:22PM -0700, Hugh Dickins wrote:
> Hi Jerome,
>
> On Wed, 27 May 2020, Jerome Glisse wrote:
> > So any arch code which uses page_mapping_file() might get the wrong
> > answer, this function will return NULL for a swap backed page which
> > can be a shmem pages. But shmem pages can still be shared among
> > multiple process (and possibly at different virtual addresses if
> > mremap was use).
> >
> > Attached is a patch that changes page_mapping_file() to return the
> > shmem mapping for swap backed shmem page. I have not tested it (no
> > way for me to test all those architecture) and i spotted this while
> > working on something else. So i hope someone can take a closer look.
>
> I'm certainly no expert on flush_dcache_page() and friends, but I'd
> be very surprised if such a problem exists, yet has gone unnoticed
> for so long. page_mapping_file() itself is fairly new, added when
> a risk of crashing on a race with swapoff came in: but the previous
> use of page_mapping() would have suffered equally if there were such
> a cache flushinhg problem here.
>
> And I'm afraid your patch won't do anything to help if there is a
> problem: very soon after shmem calls add_to_swap_cache(), it calls
> shmem_delete_from_page_cache(), which sets page->mapping to NULL.
>
> But I can assure you that a shmem page (unlike an anon page) is never
> put into swap cache while it is mapped into userspace, and never
> mapped into userspace while it is still in swap cache: does that help?
>
You are right i missed/forgot the part where shmem is never swapcache
and mapped at the same time, thus page_mapping_file() can return NULL
for those as they can no longer have alias mapping.
Thank you Hugh
Jérôme
WARNING: multiple messages have this Message-ID (diff)
From: Jerome Glisse <jglisse@redhat.com>
To: Hugh Dickins <hughd@google.com>
Cc: Rich Felker <dalias@libc.org>,
linux-sh@vger.kernel.org,
Catalin Marinas <catalin.marinas@arm.com>,
linux-mips@vger.kernel.org,
"James E.J. Bottomley" <James.Bottomley@hansenpartnership.com>,
linux-mm@kvack.org, Guo Ren <guoren@kernel.org>,
sparclinux@vger.kernel.org, Paul Burton <paulburton@kernel.org>,
Helge Deller <deller@gmx.de>, Huang Ying <ying.huang@intel.com>,
James Hogan <jhogan@kernel.org>,
rmk+kernel@arm.linux.org.uk, linux-xtensa@linux-xtensa.org,
Steven Capper <steve.capper@linaro.org>,
Rabin Vincent <rabinv@axis.com>, Ley Foon Tan <lftan@altera.com>,
Guan Xuetao <gxt@pku.edu.cn>,
linux-arm-kernel@lists.infradead.org,
Chris Zankel <chris@zankel.net>,
Yoshinori Sato <ysato@users.sourceforge.jp>,
linux-parisc@vger.kernel.org, Max Filippov <jcmvbkbc@gmail.com>,
linux-kernel@vger.kernel.org, Ralf Baechle <ralf@linux-mips.org>,
nios2-dev@lists.rocketboards.org,
Andrew Morton <akpm@linux-foundation.org>,
"David S. Miller" <davem@davemloft.net>
Subject: Re: Cache flush issue with page_mapping_file() and swap back shmem page ?
Date: Thu, 28 May 2020 07:20:25 -0400 [thread overview]
Message-ID: <20200528112025.GA10175@redhat.com> (raw)
In-Reply-To: <alpine.LSU.2.11.2005272021220.3857@eggly.anvils>
On Wed, May 27, 2020 at 08:46:22PM -0700, Hugh Dickins wrote:
> Hi Jerome,
>
> On Wed, 27 May 2020, Jerome Glisse wrote:
> > So any arch code which uses page_mapping_file() might get the wrong
> > answer, this function will return NULL for a swap backed page which
> > can be a shmem pages. But shmem pages can still be shared among
> > multiple process (and possibly at different virtual addresses if
> > mremap was use).
> >
> > Attached is a patch that changes page_mapping_file() to return the
> > shmem mapping for swap backed shmem page. I have not tested it (no
> > way for me to test all those architecture) and i spotted this while
> > working on something else. So i hope someone can take a closer look.
>
> I'm certainly no expert on flush_dcache_page() and friends, but I'd
> be very surprised if such a problem exists, yet has gone unnoticed
> for so long. page_mapping_file() itself is fairly new, added when
> a risk of crashing on a race with swapoff came in: but the previous
> use of page_mapping() would have suffered equally if there were such
> a cache flushinhg problem here.
>
> And I'm afraid your patch won't do anything to help if there is a
> problem: very soon after shmem calls add_to_swap_cache(), it calls
> shmem_delete_from_page_cache(), which sets page->mapping to NULL.
>
> But I can assure you that a shmem page (unlike an anon page) is never
> put into swap cache while it is mapped into userspace, and never
> mapped into userspace while it is still in swap cache: does that help?
>
You are right i missed/forgot the part where shmem is never swapcache
and mapped at the same time, thus page_mapping_file() can return NULL
for those as they can no longer have alias mapping.
Thank you Hugh
Jérôme
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2020-05-28 11:20 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-28 0:20 Cache flush issue with page_mapping_file() and swap back shmem page ? Jerome Glisse
2020-05-28 0:20 ` Jerome Glisse
2020-05-28 0:20 ` Jerome Glisse
2020-05-28 3:46 ` Hugh Dickins
2020-05-28 3:46 ` Hugh Dickins
2020-05-28 3:46 ` Hugh Dickins
2020-05-28 11:20 ` Jerome Glisse [this message]
2020-05-28 11:20 ` Jerome Glisse
2020-05-28 11:20 ` Jerome Glisse
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