From: Catalin Marinas <catalin.marinas@arm.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andreas Gruenbacher <agruenba@redhat.com>,
Paul Mackerras <paulus@ozlabs.org>,
Alexander Viro <viro@zeniv.linux.org.uk>,
Christoph Hellwig <hch@infradead.org>,
"Darrick J. Wong" <djwong@kernel.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,
linux-btrfs <linux-btrfs@vger.kernel.org>
Subject: Re: [PATCH v8 00/17] gfs2: Fix mmap + page fault deadlocks
Date: Wed, 27 Oct 2021 20:13:01 +0100 [thread overview]
Message-ID: <YXmkvfL9B+4mQAIo@arm.com> (raw)
In-Reply-To: <CAHk-=wjWDsB-dDj+x4yr8h8f_VSkyB7MbgGqBzDRMNz125sZxw@mail.gmail.com>
On Tue, Oct 26, 2021 at 11:50:04AM -0700, Linus Torvalds wrote:
> On Tue, Oct 26, 2021 at 11:24 AM Catalin Marinas
> <catalin.marinas@arm.com> wrote:
> > While more intrusive, I'd rather change copy_page_from_iter_atomic()
> > etc. to take a pointer where to write back an error code.
[...]
> That said, the fact that these sub-page faults are always
> non-recoverable might be a hint to a solution to the problem: maybe we
> could extend the existing return code with actual negative error
> numbers.
>
> Because for _most_ cases of "copy_to/from_user()" and friends by far,
> the only thing we look for is "zero for success".
>
> We could extend the "number of bytes _not_ copied" semantics to say
> "negative means fatal", and because there are fairly few places that
> actually look at non-zero values, we could have a coccinelle script
> that actually marks those places.
As you already replied, there are some odd places where the returned
uncopied of bytes is used. Also for some valid cases like
copy_mount_options(), it's likely that it will fall back to
byte-at-a-time with MTE since it's a good chance it would hit a fault in
a 4K page (not a fast path though). I'd have to go through all the cases
and check whether the return value is meaningful. The iter_iov.c
functions and their callers also seem to make use of the bytes copied in
case they need to call iov_iter_revert() (though I suppose the
iov_iter_iovec_advance() would skip the update in case of an error).
As an alternative, you mentioned earlier that a per-thread fault status
was not feasible on x86 due to races. Was this only for the hw poison
case? I think the uaccess is slightly different.
We can add a current->non_recoverable_uaccess variable cleared on
pagefault_disable(), only set by uaccess faults and checked by the fs
code before re-attempting the fault_in(). An interrupt shouldn't do a
uaccess (well, if it does a _nofault one, we can detect in_interrupt()
in the MTE exception handler). Last time I looked at io_uring it was
running in a separate kernel thread, not sure whether this was changed.
I don't see what else would be racing with such
current->non_recoverable_uaccess variable. If that's doable, I think
it's the least intrusive approach.
--
Catalin
next prev parent reply other threads:[~2021-10-27 19:13 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-19 13:41 [PATCH v8 00/17] gfs2: Fix mmap + page fault deadlocks Andreas Gruenbacher
2021-10-19 13:41 ` [PATCH v8 01/17] iov_iter: Fix iov_iter_get_pages{,_alloc} page fault return value Andreas Gruenbacher
2021-10-19 13:41 ` [PATCH v8 02/17] powerpc/kvm: Fix kvm_use_magic_page Andreas Gruenbacher
2021-10-19 13:41 ` [PATCH v8 03/17] gup: Turn fault_in_pages_{readable,writeable} into fault_in_{readable,writeable} Andreas Gruenbacher
2021-10-19 13:41 ` [PATCH v8 04/17] iov_iter: Turn iov_iter_fault_in_readable into fault_in_iov_iter_readable Andreas Gruenbacher
2021-10-19 13:41 ` [PATCH v8 05/17] iov_iter: Introduce fault_in_iov_iter_writeable Andreas Gruenbacher
2021-10-20 16:25 ` Catalin Marinas
2021-10-19 13:41 ` [PATCH v8 06/17] gfs2: Add wrapper for iomap_file_buffered_write Andreas Gruenbacher
2021-10-19 13:41 ` [PATCH v8 07/17] gfs2: Clean up function may_grant Andreas Gruenbacher
2021-10-19 13:41 ` [PATCH v8 08/17] gfs2: Introduce flag for glock holder auto-demotion Andreas Gruenbacher
2021-10-19 13:41 ` [PATCH v8 09/17] gfs2: Move the inode glock locking to gfs2_file_buffered_write Andreas Gruenbacher
2021-10-19 13:41 ` [PATCH v8 10/17] gfs2: Eliminate ip->i_gh Andreas Gruenbacher
2021-10-19 13:41 ` [PATCH v8 11/17] gfs2: Fix mmap + page fault deadlocks for buffered I/O Andreas Gruenbacher
2021-10-19 13:41 ` [PATCH v8 12/17] iomap: Fix iomap_dio_rw return value for user copies Andreas Gruenbacher
2021-10-19 13:42 ` [PATCH v8 13/17] iomap: Support partial direct I/O on user copy failures Andreas Gruenbacher
2021-10-19 13:42 ` [PATCH v8 14/17] iomap: Add done_before argument to iomap_dio_rw Andreas Gruenbacher
2021-10-19 15:51 ` Darrick J. Wong
2021-10-19 19:30 ` Andreas Gruenbacher
2021-10-20 1:57 ` Darrick J. Wong
2021-10-19 13:42 ` [PATCH v8 15/17] gup: Introduce FOLL_NOFAULT flag to disable page faults Andreas Gruenbacher
2021-10-19 13:42 ` [PATCH v8 16/17] iov_iter: Introduce nofault " Andreas Gruenbacher
2021-10-19 13:42 ` [PATCH v8 17/17] gfs2: Fix mmap + page fault deadlocks for direct I/O Andreas Gruenbacher
2021-10-19 15:40 ` [PATCH v8 00/17] gfs2: Fix mmap + page fault deadlocks Linus Torvalds
2021-10-19 16:00 ` Bob Peterson
2021-10-20 16:36 ` Catalin Marinas
2021-10-20 20:11 ` Linus Torvalds
2021-10-20 22:44 ` Catalin Marinas
2021-10-21 6:19 ` Linus Torvalds
2021-10-22 18:06 ` Catalin Marinas
2021-10-22 19:22 ` Linus Torvalds
2021-10-25 19:00 ` Andreas Gruenbacher
2021-10-26 18:24 ` Catalin Marinas
2021-10-26 18:50 ` Linus Torvalds
2021-10-26 19:18 ` Linus Torvalds
2021-10-27 19:13 ` Catalin Marinas [this message]
2021-10-27 21:14 ` Linus Torvalds
2021-10-28 21:20 ` Catalin Marinas
2021-10-28 21:40 ` Catalin Marinas
2021-10-28 22:15 ` Andreas Grünbacher
2021-10-29 12:50 ` Catalin Marinas
2021-10-28 22:32 ` Linus Torvalds
2021-10-29 17:50 ` Catalin Marinas
2021-10-29 18:47 ` Linus Torvalds
2021-10-25 18:24 ` Andreas Gruenbacher
2021-10-26 5:12 ` Theodore Ts'o
2021-10-26 9:44 ` Andreas Gruenbacher
2021-10-27 21:21 ` Andreas Gruenbacher
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