linux-kernel - [20/35] ext4: Resolve the hang of direct i/o read in handling EXT4_IO_END

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Date:	Fri, 26 Aug 2011 14:49:37 -0700
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Eric Sandeen <sandeen@...hat.com>, Tao Ma <boyu.mt@...bao.com>,
	"Theodore Tso" <tytso@....edu>
Subject: [20/35] ext4: Resolve the hang of direct i/o read in handling EXT4_IO_END_UNWRITTEN.

3.0-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Tao Ma <boyu.mt@...bao.com>

commit 32c80b32c053dc52712dedac5e4d0aa7c93fc353 upstream.

EXT4_IO_END_UNWRITTEN flag set and the increase of i_aiodio_unwritten
should be done simultaneously since ext4_end_io_nolock always clear
the flag and decrease the counter in the same time.

We don't increase i_aiodio_unwritten when setting
EXT4_IO_END_UNWRITTEN so it will go nagative and causes some process
to wait forever.

Part of the patch came from Eric in his e-mail, but it doesn't fix the
problem met by Michael actually.

http://marc.info/?l=linux-ext4&m=131316851417460&w=2

Reported-and-Tested-by: Michael Tokarev<mjt@....msk.ru>
Signed-off-by: Eric Sandeen <sandeen@...hat.com>
Signed-off-by: Tao Ma <boyu.mt@...bao.com>
Signed-off-by: "Theodore Ts'o" <tytso@....edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 fs/ext4/inode.c   |    9 ++++++++-
 fs/ext4/page-io.c |    6 ++++--
 2 files changed, 12 insertions(+), 3 deletions(-)

--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3645,8 +3645,15 @@ static void ext4_end_io_buffer_write(str
 		goto out;
 	}
 
-	io_end->flag = EXT4_IO_END_UNWRITTEN;
+	/*
+	 * It may be over-defensive here to check EXT4_IO_END_UNWRITTEN now,
+	 * but being more careful is always safe for the future change.
+	 */
 	inode = io_end->inode;
+	if (!(io_end->flag & EXT4_IO_END_UNWRITTEN)) {
+		io_end->flag |= EXT4_IO_END_UNWRITTEN;
+		atomic_inc(&EXT4_I(inode)->i_aiodio_unwritten);
+	}
 
 	/* Add the io_end to per-inode completed io list*/
 	spin_lock_irqsave(&EXT4_I(inode)->i_completed_io_lock, flags);
--- a/fs/ext4/page-io.c
+++ b/fs/ext4/page-io.c
@@ -338,8 +338,10 @@ submit_and_retry:
 	if ((io_end->num_io_pages >= MAX_IO_PAGES) &&
 	    (io_end->pages[io_end->num_io_pages-1] != io_page))
 		goto submit_and_retry;
-	if (buffer_uninit(bh))
-		io->io_end->flag |= EXT4_IO_END_UNWRITTEN;
+	if (buffer_uninit(bh) && !(io_end->flag & EXT4_IO_END_UNWRITTEN)) {
+		io_end->flag |= EXT4_IO_END_UNWRITTEN;
+		atomic_inc(&EXT4_I(inode)->i_aiodio_unwritten);
+	}
 	io->io_end->size += bh->b_size;
 	io->io_next_block++;
 	ret = bio_add_page(io->io_bio, bh->b_page, bh->b_size, bh_offset(bh));


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