Linux-Fsdevel Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Dave Chinner <david@fromorbit.com>
To: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: Christoph Hellwig <hch@infradead.org>,
	"Darrick J. Wong" <darrick.wong@oracle.com>,
	linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	Brian Foster <bfoster@redhat.com>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] iomap: Ensure iop->uptodate matches PageUptodate
Date: Mon, 27 Jul 2020 09:06:57 +1000	[thread overview]
Message-ID: <20200726230657.GT2005@dread.disaster.area> (raw)
In-Reply-To: <20200726091052.30576-1-willy@infradead.org>

On Sun, Jul 26, 2020 at 10:10:52AM +0100, Matthew Wilcox (Oracle) wrote:
> If the filesystem has block size < page size and we end up calling
> iomap_page_create() in iomap_page_mkwrite_actor(), the uptodate bits
> would be zero, which causes us to skip writeback of blocks which are
> !uptodate in iomap_writepage_map().  This can lead to user data loss.

I'm still unclear on what condition gets us to
iomap_page_mkwrite_actor() without already having initialised the
page correctly. i.e. via a read() or write() call, or the read fault
prior to ->page_mkwrite() which would have marked the page uptodate
- that operation should have called iomap_page_create() and
iomap_set_range_uptodate() on the page....

i.e. you've described the symptom, but not the cause of the issue
you are addressing.

> Found using generic/127 with the THP patches.  I don't think this can be
> reproduced on mainline using that test (the THP code causes iomap_pages
> to be discarded more frequently), but inspection shows it can happen
> with an appropriate series of operations.

That sequence of operations would be? 

> Fixes: 9dc55f1389f9 ("iomap: add support for sub-pagesize buffered I/O without buffer heads")
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> ---
>  fs/iomap/buffered-io.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> index a2b3b5455219..f0c5027bf33f 100644
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c
> @@ -53,7 +53,10 @@ iomap_page_create(struct inode *inode, struct page *page)
>  	atomic_set(&iop->read_count, 0);
>  	atomic_set(&iop->write_count, 0);
>  	spin_lock_init(&iop->uptodate_lock);
> -	bitmap_zero(iop->uptodate, PAGE_SIZE / SECTOR_SIZE);
> +	if (PageUptodate(page))
> +		bitmap_fill(iop->uptodate, PAGE_SIZE / SECTOR_SIZE);
> +	else
> +		bitmap_zero(iop->uptodate, PAGE_SIZE / SECTOR_SIZE);

I suspect this bitmap_fill call belongs in the iomap_page_mkwrite()
code as is the only code that can call iomap_page_create() with an
uptodate page. Then iomap_page_create() could just use kzalloc() and
drop the atomic_set() and bitmap_zero() calls altogether,

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com

  parent reply	other threads:[~2020-07-26 23:07 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-26  9:10 Matthew Wilcox (Oracle)
2020-07-26 15:15 ` Christoph Hellwig
2020-07-26 23:06 ` Dave Chinner [this message]
2020-07-26 23:20   ` Matthew Wilcox
2020-07-26 23:53     ` Dave Chinner
2020-07-28  9:23       ` Christoph Hellwig
2020-07-28 13:15         ` Matthew Wilcox

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=20200726230657.GT2005@dread.disaster.area \
    --to=david@fromorbit.com \
    --cc=bfoster@redhat.com \
    --cc=darrick.wong@oracle.com \
    --cc=hch@infradead.org \
    --cc=linux-fsdevel@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-xfs@vger.kernel.org \
    --cc=willy@infradead.org \
    --subject='Re: [PATCH] iomap: Ensure iop->uptodate matches PageUptodate' \
    /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

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).