From: Al Viro <viro@zeniv.linux.org.uk>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: cluster-devel <cluster-devel@redhat.com>, Jan Kara <jack@suse.cz>,
Andreas Gruenbacher <agruenba@redhat.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Christoph Hellwig <hch@infradead.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
ocfs2-devel@oss.oracle.com
Subject: Re: [Ocfs2-devel] [PATCH v4 1/8] iov_iter: Introduce iov_iter_fault_in_writeable helper
Date: Sat, 24 Jul 2021 20:24:17 +0000 [thread overview]
Message-ID: <YPx28cEvrVl6YrDk@zeniv-ca.linux.org.uk> (raw)
In-Reply-To: <CAHk-=whodi=ZPhoJy_a47VD+-aFtz385B4_GHvQp8Bp9NdTKUg@mail.gmail.com>
On Sat, Jul 24, 2021 at 12:52:34PM -0700, Linus Torvalds wrote:
> ...
> > + if (fault_in_user_pages(start, len, true) != len)
> > + return -EFAULT;
>
> Looking at this once more, I think this is likely wrong.
>
> Why?
>
> Because any user can/should only care about at least *part* of the
> area being writable.
>
> Imagine that you're doing a large read. If the *first* page is
> writable, you should still return the partial read, not -EFAULT.
Agreed.
> So I think the code needs to return 0 if _any_ fault was successful.
s/any/the first/...
The same goes for fault-in for read, of course; I've a half-baked conversion
to such semantics (-EFAULT vs. 0; precise length is unreliable anyway,
especially if you have sub-page failure areas), need to finish and post
it...
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next prev parent reply other threads:[~2021-07-24 20:26 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-24 19:34 [Ocfs2-devel] [PATCH v4 0/8] gfs2: Fix mmap + page fault deadlocks Andreas Gruenbacher
2021-07-24 19:34 ` [Ocfs2-devel] [PATCH v4 1/8] iov_iter: Introduce iov_iter_fault_in_writeable helper Andreas Gruenbacher
2021-07-24 19:52 ` Linus Torvalds
2021-07-24 20:24 ` Al Viro [this message]
2021-07-24 20:37 ` Linus Torvalds
2021-07-24 21:38 ` Andreas Gruenbacher
2021-07-24 21:57 ` Al Viro
2021-07-24 22:06 ` Andreas Gruenbacher
2021-07-24 23:39 ` Al Viro
2021-07-27 9:30 ` David Laight
2021-07-27 11:13 ` Andreas Gruenbacher
2021-07-27 17:51 ` Linus Torvalds
2021-07-24 19:34 ` [Ocfs2-devel] [PATCH v4 2/8] gfs2: Add wrapper for iomap_file_buffered_write Andreas Gruenbacher
2021-07-24 19:34 ` [Ocfs2-devel] [PATCH v4 3/8] gfs2: Fix mmap + page fault deadlocks for buffered I/O Andreas Gruenbacher
2021-07-24 19:34 ` [Ocfs2-devel] [PATCH v4 4/8] iomap: Fix iomap_dio_rw return value for user copies Andreas Gruenbacher
2021-07-24 19:34 ` [Ocfs2-devel] [PATCH v4 5/8] iomap: Add done_before argument to iomap_dio_rw Andreas Gruenbacher
2021-07-24 19:34 ` [Ocfs2-devel] [PATCH v4 6/8] iomap: Support restarting direct I/O requests after user copy failures Andreas Gruenbacher
2021-07-24 19:34 ` [Ocfs2-devel] [PATCH v4 7/8] iov_iter: Introduce noio flag to disable page faults Andreas Gruenbacher
2021-07-24 19:34 ` [Ocfs2-devel] [PATCH v4 8/8] gfs2: Fix mmap + page fault deadlocks for direct I/O Andreas Gruenbacher
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