From: Jan Kara <jack@suse.cz>
To: Andreas Gruenbacher <agruenba@redhat.com>
Cc: cluster-devel@redhat.com, Jan Kara <jack@suse.cz>,
linux-kernel@vger.kernel.org,
Christoph Hellwig <hch@infradead.org>,
Alexander Viro <viro@zeniv.linux.org.uk>,
linux-fsdevel@vger.kernel.org,
Linus Torvalds <torvalds@linux-foundation.org>,
ocfs2-devel@oss.oracle.com
Subject: Re: [Ocfs2-devel] [PATCH v3 1/7] iov_iter: Introduce fault_in_iov_iter helper
Date: Mon, 26 Jul 2021 18:33:26 +0200 [thread overview]
Message-ID: <20210726163326.GK20621@quack2.suse.cz> (raw)
In-Reply-To: <20210723205840.299280-2-agruenba@redhat.com>
On Fri 23-07-21 22:58:34, Andreas Gruenbacher wrote:
> Introduce a new fault_in_iov_iter helper for manually faulting in an iterator.
> Other than fault_in_pages_writeable(), this function is non-destructive.
>
> We'll use fault_in_iov_iter in gfs2 once we've determined that the iterator
> passed to .read_iter or .write_iter isn't in memory.
>
> Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
...
> +unsigned long fault_in_user_pages(unsigned long start, unsigned long len,
> + bool write)
> +{
> + struct mm_struct *mm = current->mm;
> + struct vm_area_struct *vma = NULL;
> + unsigned long end, nstart, nend;
> + int locked = 0;
> + int gup_flags;
> +
> + /*
> + * FIXME: Make sure this function doesn't succeed for pages that cannot
> + * be accessed; otherwise we could end up in a loop trying to fault in
> + * and then access the pages. (It's okay if a page gets evicted and we
> + * need more than one retry.)
> + */
> +
> + /*
> + * FIXME: Are these the right FOLL_* flags?
> + */
How about the FIXMEs here? I guess we should answer these questions before
merging and remove the comments. Regarding the first FIXME I tend to agree
that if we cannot fault in the first page, we should return the error
rather than returning 0 as you do now. OTOH the caller can check for 0 and
understand there's something wrong going on as well. But the error would be
probably a bit clearer.
> +
> + gup_flags = FOLL_TOUCH | FOLL_POPULATE;
I don't think FOLL_POPULATE makes sense here. It makes sense only with
FOLL_MLOCK and determines whether mlock(2) should fault in missing pages or
not.
Honza
> + if (write)
> + gup_flags |= FOLL_WRITE;
> +
> + end = PAGE_ALIGN(start + len);
> + for (nstart = start & PAGE_MASK; nstart < end; nstart = nend) {
> + unsigned long nr_pages;
> + long ret;
> +
> + if (!locked) {
> + locked = 1;
> + mmap_read_lock(mm);
> + vma = find_vma(mm, nstart);
> + } else if (nstart >= vma->vm_end)
> + vma = vma->vm_next;
> + if (!vma || vma->vm_start >= end)
> + break;
> + nend = min(end, vma->vm_end);
> + if (vma->vm_flags & (VM_IO | VM_PFNMAP))
> + continue;
> + if (nstart < vma->vm_start)
> + nstart = vma->vm_start;
> + nr_pages = (nend - nstart) / PAGE_SIZE;
> + ret = __get_user_pages_locked(mm, nstart, nr_pages,
> + NULL, NULL, &locked, gup_flags);
> + if (ret <= 0)
> + break;
> + nend = nstart + ret * PAGE_SIZE;
> + }
> + if (locked)
> + mmap_read_unlock(mm);
> + if (nstart > start)
> + return min(nstart - start, len);
> + return 0;
> +}
> +
> /**
> * get_dump_page() - pin user page in memory while writing it to core dump
> * @addr: user address
> --
> 2.26.3
>
--
Jan Kara <jack@suse.com>
SUSE Labs, CR
_______________________________________________
Ocfs2-devel mailing list
Ocfs2-devel@oss.oracle.com
https://oss.oracle.com/mailman/listinfo/ocfs2-devel
next prev parent reply other threads:[~2021-07-26 16:34 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-23 20:58 [Ocfs2-devel] [PATCH v3 0/7] gfs2: Fix mmap + page fault deadlocks Andreas Gruenbacher
2021-07-23 20:58 ` [Ocfs2-devel] [PATCH v3 1/7] iov_iter: Introduce fault_in_iov_iter helper Andreas Gruenbacher
2021-07-23 23:40 ` Linus Torvalds
2021-07-24 7:51 ` Andreas Grünbacher
2021-07-24 1:52 ` Al Viro
2021-07-24 8:05 ` Andreas Grünbacher
2021-07-26 16:33 ` Jan Kara [this message]
2021-07-26 17:15 ` Linus Torvalds
2021-07-23 20:58 ` [Ocfs2-devel] [PATCH v3 2/7] gfs2: Add wrapper for iomap_file_buffered_write Andreas Gruenbacher
2021-07-23 20:58 ` [Ocfs2-devel] [PATCH v3 3/7] gfs2: Fix mmap + page fault deadlocks for buffered I/O Andreas Gruenbacher
2021-07-23 20:58 ` [Ocfs2-devel] [PATCH v3 4/7] iomap: Fix iomap_dio_rw return value for user copies Andreas Gruenbacher
2021-07-23 20:58 ` [Ocfs2-devel] [PATCH v3 5/7] iomap: Support restarting direct I/O requests after user copy failures Andreas Gruenbacher
2021-07-26 17:19 ` Jan Kara
2021-07-26 17:45 ` Andreas Grünbacher
2021-07-26 18:08 ` Jan Kara
2021-07-23 20:58 ` [Ocfs2-devel] [PATCH v3 6/7] iov_iter: Introduce noio flag to disable page faults Andreas Gruenbacher
2021-07-23 20:58 ` [Ocfs2-devel] [PATCH v3 7/7] gfs2: Fix mmap + page fault deadlocks for direct I/O Andreas Gruenbacher
2021-07-26 17:02 ` Jan Kara
2021-07-26 17:50 ` Andreas Grünbacher
2021-07-26 18:00 ` Jan Kara
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=20210726163326.GK20621@quack2.suse.cz \
--to=jack@suse.cz \
--cc=agruenba@redhat.com \
--cc=cluster-devel@redhat.com \
--cc=hch@infradead.org \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=ocfs2-devel@oss.oracle.com \
--cc=torvalds@linux-foundation.org \
--cc=viro@zeniv.linux.org.uk \
/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 a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).