From: Linus Torvalds <torvalds@linux-foundation.org>
To: Andreas Gruenbacher <agruenba@redhat.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>,
Christoph Hellwig <hch@infradead.org>,
"Darrick J. Wong" <djwong@kernel.org>,
Paul Mackerras <paulus@ozlabs.org>, Jan Kara <jack@suse.cz>,
Matthew Wilcox <willy@infradead.org>,
cluster-devel <cluster-devel@redhat.com>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
ocfs2-devel@oss.oracle.com, kvm-ppc@vger.kernel.org
Subject: Re: [PATCH v5 00/12] gfs2: Fix mmap + page fault deadlocks
Date: Wed, 18 Aug 2021 14:49:28 -0700 [thread overview]
Message-ID: <CAHk-=whBCm3G5yibbvQsTn00fA16a688NTU_geQV158DnRy+bQ@mail.gmail.com> (raw)
In-Reply-To: <CAHc6FU6H5q20qiQ5FX1726i0FJHyh=Y46huWkCBZTR3sk+3Dhg@mail.gmail.com>
[ Sorry for the delay, I was on the road and this fell through the cracks ]
On Mon, Aug 16, 2021 at 12:14 PM Andreas Gruenbacher
<agruenba@redhat.com> wrote:
>
> On Tue, Aug 3, 2021 at 9:45 PM Linus Torvalds
> <torvalds@linux-foundation.org> wrote:
> >
> > Hmm. Have you tried to figure out why that "still returns 0" happens?
>
> The call stack is:
>
> gup_pte_range
> gup_pmd_range
> gup_pud_range
> gup_p4d_range
> gup_pgd_range
> lockless_pages_from_mm
> internal_get_user_pages_fast
> get_user_pages_fast
> iov_iter_get_pages
> __bio_iov_iter_get_pages
> bio_iov_iter_get_pages
> iomap_dio_bio_actor
> iomap_dio_actor
> iomap_apply
> iomap_dio_rw
> gfs2_file_direct_write
>
> In gup_pte_range, pte_special(pte) is true and so we return 0.
Ok, so that is indeed something that the fast-case can't handle,
because some of the special code wants to have the mm_lock so that it
can look at the vma flags (eg "vm_normal_page()" and friends.
That said, some of these cases even the full GUP won't ever handle,
simply because a mapping doesn't necessarily even _have_ a 'struct
page' associated with it if it's a VM_IO mapping.
So it turns out that you can't just always do
fault_in_iov_iter_readable() and then assume that you can do
iov_iter_get_pages() and repeat until successful.
We could certainly make get_user_pages_fast() handle a few more cases,
but I get the feeling that we need to have separate error cases for
EFAULT - no page exists - and the "page exists, but cannot be mapped
as a 'struct page'" case.
I also do still think that even regardless of that, we want to just
add a FOLL_NOFAULT flag that just disables calling handle_mm_fault(),
and then you can use the regular get_user_pages().
That at least gives us the full _normal_ page handling stuff.
Linus
WARNING: multiple messages have this Message-ID (diff)
From: Linus Torvalds <torvalds@linux-foundation.org>
To: Andreas Gruenbacher <agruenba@redhat.com>
Cc: kvm-ppc@vger.kernel.org, Paul Mackerras <paulus@ozlabs.org>,
cluster-devel <cluster-devel@redhat.com>, Jan Kara <jack@suse.cz>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Christoph Hellwig <hch@infradead.org>,
Alexander Viro <viro@zeniv.linux.org.uk>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
ocfs2-devel@oss.oracle.com
Subject: Re: [Ocfs2-devel] [PATCH v5 00/12] gfs2: Fix mmap + page fault deadlocks
Date: Wed, 18 Aug 2021 14:49:28 -0700 [thread overview]
Message-ID: <CAHk-=whBCm3G5yibbvQsTn00fA16a688NTU_geQV158DnRy+bQ@mail.gmail.com> (raw)
In-Reply-To: <CAHc6FU6H5q20qiQ5FX1726i0FJHyh=Y46huWkCBZTR3sk+3Dhg@mail.gmail.com>
[ Sorry for the delay, I was on the road and this fell through the cracks ]
On Mon, Aug 16, 2021 at 12:14 PM Andreas Gruenbacher
<agruenba@redhat.com> wrote:
>
> On Tue, Aug 3, 2021 at 9:45 PM Linus Torvalds
> <torvalds@linux-foundation.org> wrote:
> >
> > Hmm. Have you tried to figure out why that "still returns 0" happens?
>
> The call stack is:
>
> gup_pte_range
> gup_pmd_range
> gup_pud_range
> gup_p4d_range
> gup_pgd_range
> lockless_pages_from_mm
> internal_get_user_pages_fast
> get_user_pages_fast
> iov_iter_get_pages
> __bio_iov_iter_get_pages
> bio_iov_iter_get_pages
> iomap_dio_bio_actor
> iomap_dio_actor
> iomap_apply
> iomap_dio_rw
> gfs2_file_direct_write
>
> In gup_pte_range, pte_special(pte) is true and so we return 0.
Ok, so that is indeed something that the fast-case can't handle,
because some of the special code wants to have the mm_lock so that it
can look at the vma flags (eg "vm_normal_page()" and friends.
That said, some of these cases even the full GUP won't ever handle,
simply because a mapping doesn't necessarily even _have_ a 'struct
page' associated with it if it's a VM_IO mapping.
So it turns out that you can't just always do
fault_in_iov_iter_readable() and then assume that you can do
iov_iter_get_pages() and repeat until successful.
We could certainly make get_user_pages_fast() handle a few more cases,
but I get the feeling that we need to have separate error cases for
EFAULT - no page exists - and the "page exists, but cannot be mapped
as a 'struct page'" case.
I also do still think that even regardless of that, we want to just
add a FOLL_NOFAULT flag that just disables calling handle_mm_fault(),
and then you can use the regular get_user_pages().
That at least gives us the full _normal_ page handling stuff.
Linus
_______________________________________________
Ocfs2-devel mailing list
Ocfs2-devel@oss.oracle.com
https://oss.oracle.com/mailman/listinfo/ocfs2-devel
WARNING: multiple messages have this Message-ID (diff)
From: Linus Torvalds <torvalds@linux-foundation.org>
To: cluster-devel.redhat.com
Subject: [Cluster-devel] [PATCH v5 00/12] gfs2: Fix mmap + page fault deadlocks
Date: Wed, 18 Aug 2021 14:49:28 -0700 [thread overview]
Message-ID: <CAHk-=whBCm3G5yibbvQsTn00fA16a688NTU_geQV158DnRy+bQ@mail.gmail.com> (raw)
In-Reply-To: <CAHc6FU6H5q20qiQ5FX1726i0FJHyh=Y46huWkCBZTR3sk+3Dhg@mail.gmail.com>
[ Sorry for the delay, I was on the road and this fell through the cracks ]
On Mon, Aug 16, 2021 at 12:14 PM Andreas Gruenbacher
<agruenba@redhat.com> wrote:
>
> On Tue, Aug 3, 2021 at 9:45 PM Linus Torvalds
> <torvalds@linux-foundation.org> wrote:
> >
> > Hmm. Have you tried to figure out why that "still returns 0" happens?
>
> The call stack is:
>
> gup_pte_range
> gup_pmd_range
> gup_pud_range
> gup_p4d_range
> gup_pgd_range
> lockless_pages_from_mm
> internal_get_user_pages_fast
> get_user_pages_fast
> iov_iter_get_pages
> __bio_iov_iter_get_pages
> bio_iov_iter_get_pages
> iomap_dio_bio_actor
> iomap_dio_actor
> iomap_apply
> iomap_dio_rw
> gfs2_file_direct_write
>
> In gup_pte_range, pte_special(pte) is true and so we return 0.
Ok, so that is indeed something that the fast-case can't handle,
because some of the special code wants to have the mm_lock so that it
can look at the vma flags (eg "vm_normal_page()" and friends.
That said, some of these cases even the full GUP won't ever handle,
simply because a mapping doesn't necessarily even _have_ a 'struct
page' associated with it if it's a VM_IO mapping.
So it turns out that you can't just always do
fault_in_iov_iter_readable() and then assume that you can do
iov_iter_get_pages() and repeat until successful.
We could certainly make get_user_pages_fast() handle a few more cases,
but I get the feeling that we need to have separate error cases for
EFAULT - no page exists - and the "page exists, but cannot be mapped
as a 'struct page'" case.
I also do still think that even regardless of that, we want to just
add a FOLL_NOFAULT flag that just disables calling handle_mm_fault(),
and then you can use the regular get_user_pages().
That at least gives us the full _normal_ page handling stuff.
Linus
WARNING: multiple messages have this Message-ID (diff)
From: Linus Torvalds <torvalds@linux-foundation.org>
To: Andreas Gruenbacher <agruenba@redhat.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>,
Christoph Hellwig <hch@infradead.org>,
"Darrick J. Wong" <djwong@kernel.org>,
Paul Mackerras <paulus@ozlabs.org>, Jan Kara <jack@suse.cz>,
Matthew Wilcox <willy@infradead.org>,
cluster-devel <cluster-devel@redhat.com>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
ocfs2-devel@oss.oracle.com, kvm-ppc@vger.kernel.org
Subject: Re: [PATCH v5 00/12] gfs2: Fix mmap + page fault deadlocks
Date: Wed, 18 Aug 2021 21:49:28 +0000 [thread overview]
Message-ID: <CAHk-=whBCm3G5yibbvQsTn00fA16a688NTU_geQV158DnRy+bQ@mail.gmail.com> (raw)
In-Reply-To: <CAHc6FU6H5q20qiQ5FX1726i0FJHyh=Y46huWkCBZTR3sk+3Dhg@mail.gmail.com>
[ Sorry for the delay, I was on the road and this fell through the cracks ]
On Mon, Aug 16, 2021 at 12:14 PM Andreas Gruenbacher
<agruenba@redhat.com> wrote:
>
> On Tue, Aug 3, 2021 at 9:45 PM Linus Torvalds
> <torvalds@linux-foundation.org> wrote:
> >
> > Hmm. Have you tried to figure out why that "still returns 0" happens?
>
> The call stack is:
>
> gup_pte_range
> gup_pmd_range
> gup_pud_range
> gup_p4d_range
> gup_pgd_range
> lockless_pages_from_mm
> internal_get_user_pages_fast
> get_user_pages_fast
> iov_iter_get_pages
> __bio_iov_iter_get_pages
> bio_iov_iter_get_pages
> iomap_dio_bio_actor
> iomap_dio_actor
> iomap_apply
> iomap_dio_rw
> gfs2_file_direct_write
>
> In gup_pte_range, pte_special(pte) is true and so we return 0.
Ok, so that is indeed something that the fast-case can't handle,
because some of the special code wants to have the mm_lock so that it
can look at the vma flags (eg "vm_normal_page()" and friends.
That said, some of these cases even the full GUP won't ever handle,
simply because a mapping doesn't necessarily even _have_ a 'struct
page' associated with it if it's a VM_IO mapping.
So it turns out that you can't just always do
fault_in_iov_iter_readable() and then assume that you can do
iov_iter_get_pages() and repeat until successful.
We could certainly make get_user_pages_fast() handle a few more cases,
but I get the feeling that we need to have separate error cases for
EFAULT - no page exists - and the "page exists, but cannot be mapped
as a 'struct page'" case.
I also do still think that even regardless of that, we want to just
add a FOLL_NOFAULT flag that just disables calling handle_mm_fault(),
and then you can use the regular get_user_pages().
That at least gives us the full _normal_ page handling stuff.
Linus
next prev parent reply other threads:[~2021-08-18 21:49 UTC|newest]
Thread overview: 77+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-03 19:18 [PATCH v5 00/12] gfs2: Fix mmap + page fault deadlocks Andreas Gruenbacher
2021-08-03 19:18 ` Andreas Gruenbacher
2021-08-03 19:18 ` [Cluster-devel] " Andreas Gruenbacher
2021-08-03 19:18 ` [Ocfs2-devel] " Andreas Gruenbacher
2021-08-03 19:18 ` [PATCH v5 01/12] iov_iter: Fix iov_iter_get_pages{,_alloc} page fault return value Andreas Gruenbacher
2021-08-03 19:18 ` [Cluster-devel] [PATCH v5 01/12] iov_iter: Fix iov_iter_get_pages{, _alloc} " Andreas Gruenbacher
2021-08-03 19:18 ` [Ocfs2-devel] " Andreas Gruenbacher
2021-08-03 19:18 ` [PATCH v5 02/12] powerpc/kvm: Fix kvm_use_magic_page Andreas Gruenbacher
2021-08-03 19:18 ` Andreas Gruenbacher
2021-08-03 19:18 ` [Cluster-devel] " Andreas Gruenbacher
2021-08-03 19:18 ` [Ocfs2-devel] " Andreas Gruenbacher
2021-08-03 19:18 ` [PATCH v5 03/12] Turn fault_in_pages_{readable,writeable} into fault_in_{readable,writeable} Andreas Gruenbacher
2021-08-03 19:18 ` [Cluster-devel] [PATCH v5 03/12] Turn fault_in_pages_{readable, writeable} into fault_in_{readable, writeable} Andreas Gruenbacher
2021-08-03 19:18 ` [Ocfs2-devel] " Andreas Gruenbacher
2021-08-03 19:43 ` [PATCH v5 03/12] Turn fault_in_pages_{readable,writeable} into fault_in_{readable,writeable} Linus Torvalds
2021-08-03 19:43 ` [Cluster-devel] [PATCH v5 03/12] Turn fault_in_pages_{readable, writeable} into fault_in_{readable, writeable} Linus Torvalds
2021-08-03 19:43 ` [Ocfs2-devel] " Linus Torvalds
2021-08-03 20:57 ` [PATCH v5 03/12] Turn fault_in_pages_{readable,writeable} into fault_in_{readable,writeable} Al Viro
2021-08-03 20:57 ` [Cluster-devel] [PATCH v5 03/12] Turn fault_in_pages_{readable, writeable} into fault_in_{readable, writeable} Al Viro
2021-08-03 20:57 ` [Ocfs2-devel] " Al Viro
2021-08-03 21:38 ` [PATCH v5 03/12] Turn fault_in_pages_{readable,writeable} into fault_in_{readable,writeable} Andreas Gruenbacher
2021-08-03 21:38 ` [Cluster-devel] [PATCH v5 03/12] Turn fault_in_pages_{readable, writeable} into fault_in_{readable, writeable} Andreas Gruenbacher
2021-08-03 21:38 ` [Ocfs2-devel] " Andreas Gruenbacher
2021-08-03 19:18 ` [PATCH v5 04/12] Turn iov_iter_fault_in_readable into fault_in_iov_iter_readable Andreas Gruenbacher
2021-08-03 19:18 ` [Cluster-devel] " Andreas Gruenbacher
2021-08-03 19:18 ` [Ocfs2-devel] " Andreas Gruenbacher
2021-08-03 19:18 ` [PATCH v5 05/12] iov_iter: Introduce fault_in_iov_iter_writeable Andreas Gruenbacher
2021-08-03 19:18 ` [Cluster-devel] " Andreas Gruenbacher
2021-08-03 19:18 ` [Ocfs2-devel] " Andreas Gruenbacher
2021-08-04 15:24 ` Andreas Gruenbacher
2021-08-04 15:24 ` [Cluster-devel] " Andreas Gruenbacher
2021-08-04 15:24 ` [Ocfs2-devel] " Andreas Gruenbacher
2021-08-03 19:18 ` [PATCH v5 06/12] gfs2: Add wrapper for iomap_file_buffered_write Andreas Gruenbacher
2021-08-03 19:18 ` [Cluster-devel] " Andreas Gruenbacher
2021-08-03 19:18 ` [Ocfs2-devel] " Andreas Gruenbacher
2021-08-03 19:18 ` [PATCH v5 07/12] gfs2: Fix mmap + page fault deadlocks for buffered I/O Andreas Gruenbacher
2021-08-03 19:18 ` [Cluster-devel] " Andreas Gruenbacher
2021-08-03 19:18 ` [Ocfs2-devel] " Andreas Gruenbacher
2021-08-03 19:18 ` [PATCH v5 08/12] iomap: Fix iomap_dio_rw return value for user copies Andreas Gruenbacher
2021-08-03 19:18 ` [Cluster-devel] " Andreas Gruenbacher
2021-08-03 19:18 ` [Ocfs2-devel] " Andreas Gruenbacher
2021-08-03 19:18 ` [PATCH v5 09/12] iomap: Support restarting direct I/O requests after user copy failures Andreas Gruenbacher
2021-08-03 19:18 ` [Cluster-devel] " Andreas Gruenbacher
2021-08-03 19:18 ` [Ocfs2-devel] " Andreas Gruenbacher
2021-08-03 19:18 ` [PATCH v5 10/12] iomap: Add done_before argument to iomap_dio_rw Andreas Gruenbacher
2021-08-03 19:18 ` [Cluster-devel] " Andreas Gruenbacher
2021-08-03 19:18 ` [Ocfs2-devel] " Andreas Gruenbacher
2021-08-03 19:18 ` [PATCH v5 11/12] iov_iter: Introduce noio flag to disable page faults Andreas Gruenbacher
2021-08-03 19:18 ` [Cluster-devel] " Andreas Gruenbacher
2021-08-03 19:18 ` [Ocfs2-devel] " Andreas Gruenbacher
2021-08-03 19:18 ` [PATCH v5 12/12] gfs2: Fix mmap + page fault deadlocks for direct I/O Andreas Gruenbacher
2021-08-03 19:18 ` [Cluster-devel] " Andreas Gruenbacher
2021-08-03 19:18 ` [Ocfs2-devel] " Andreas Gruenbacher
2021-08-03 19:45 ` [PATCH v5 00/12] gfs2: Fix mmap + page fault deadlocks Linus Torvalds
2021-08-03 19:45 ` Linus Torvalds
2021-08-03 19:45 ` [Cluster-devel] " Linus Torvalds
2021-08-03 19:45 ` [Ocfs2-devel] " Linus Torvalds
2021-08-16 19:14 ` Andreas Gruenbacher
2021-08-16 19:14 ` Andreas Gruenbacher
2021-08-16 19:14 ` [Cluster-devel] " Andreas Gruenbacher
2021-08-16 19:14 ` [Ocfs2-devel] " Andreas Gruenbacher
2021-08-18 21:49 ` Linus Torvalds [this message]
2021-08-18 21:49 ` Linus Torvalds
2021-08-18 21:49 ` [Cluster-devel] " Linus Torvalds
2021-08-18 21:49 ` [Ocfs2-devel] " Linus Torvalds
2021-08-19 19:40 ` Andreas Gruenbacher
2021-08-19 19:40 ` Andreas Gruenbacher
2021-08-19 19:40 ` [Cluster-devel] " Andreas Gruenbacher
2021-08-19 19:40 ` [Ocfs2-devel] " Andreas Gruenbacher
2021-08-19 20:14 ` Linus Torvalds
2021-08-19 20:14 ` Linus Torvalds
2021-08-19 20:14 ` [Cluster-devel] " Linus Torvalds
2021-08-19 20:14 ` [Ocfs2-devel] " Linus Torvalds
2021-08-19 21:39 ` Andreas Gruenbacher
2021-08-19 21:39 ` Andreas Gruenbacher
2021-08-19 21:39 ` [Cluster-devel] " Andreas Gruenbacher
2021-08-19 21:39 ` [Ocfs2-devel] " Andreas Gruenbacher
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to='CAHk-=whBCm3G5yibbvQsTn00fA16a688NTU_geQV158DnRy+bQ@mail.gmail.com' \
--to=torvalds@linux-foundation.org \
--cc=agruenba@redhat.com \
--cc=cluster-devel@redhat.com \
--cc=djwong@kernel.org \
--cc=hch@infradead.org \
--cc=jack@suse.cz \
--cc=kvm-ppc@vger.kernel.org \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=ocfs2-devel@oss.oracle.com \
--cc=paulus@ozlabs.org \
--cc=viro@zeniv.linux.org.uk \
--cc=willy@infradead.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.