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From: Dave Jiang <dave.jiang@intel.com>
To: tytso@mit.edu, darrick.wong@oracle.com, jack@suse.cz, zwisler@kernel.org
Cc: linux-nvdimm@lists.01.org, david@fromorbit.com,
	linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	lczerner@redhat.com, linux-ext4@vger.kernel.org, hch@lst.de
Subject: [PATCH 1/2] ext4: Close race between direct IO and ext4_break_layouts()
Date: Tue, 07 Aug 2018 15:11:37 -0700	[thread overview]
Message-ID: <153367989755.37314.6889218648604435494.stgit@djiang5-desk3.ch.intel.com> (raw)

From: Ross Zwisler <zwisler@kernel.org>

If the refcount of a page is lowered between the time that it is returned
by dax_busy_page() and when the refcount is again checked in
ext4_break_layouts() => ___wait_var_event(), the waiting function
ext4_wait_dax_page() will never be called.  This means that
ext4_break_layouts() will still have 'retry' set to false, so we'll stop
looping and never check the refcount of other pages in this inode.

Instead, always continue looping as long as dax_layout_busy_page() gives us
a page which it found with an elevated refcount.

Note that this works around the race exposed by my unit test, but I think
that there is another race that needs to be addressed, probably with
additional synchronization added between direct I/O and
{ext4,xfs}_break_layouts().

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Reviewed-by: Jan Kara <jack@suse.cz>
---
 fs/ext4/inode.c |    9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 8f6ad7667974..d2663a1e3ec2 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -4191,9 +4191,8 @@ int ext4_update_disksize_before_punch(struct inode *inode, loff_t offset,
 	return 0;
 }
 
-static void ext4_wait_dax_page(struct ext4_inode_info *ei, bool *did_unlock)
+static void ext4_wait_dax_page(struct ext4_inode_info *ei)
 {
-	*did_unlock = true;
 	up_write(&ei->i_mmap_sem);
 	schedule();
 	down_write(&ei->i_mmap_sem);
@@ -4203,14 +4202,12 @@ int ext4_break_layouts(struct inode *inode)
 {
 	struct ext4_inode_info *ei = EXT4_I(inode);
 	struct page *page;
-	bool retry;
 	int error;
 
 	if (WARN_ON_ONCE(!rwsem_is_locked(&ei->i_mmap_sem)))
 		return -EINVAL;
 
 	do {
-		retry = false;
 		page = dax_layout_busy_page(inode->i_mapping);
 		if (!page)
 			return 0;
@@ -4218,8 +4215,8 @@ int ext4_break_layouts(struct inode *inode)
 		error = ___wait_var_event(&page->_refcount,
 				atomic_read(&page->_refcount) == 1,
 				TASK_INTERRUPTIBLE, 0, 0,
-				ext4_wait_dax_page(ei, &retry));
-	} while (error == 0 && retry);
+				ext4_wait_dax_page(ei));
+	} while (error == 0);
 
 	return error;
 }

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             reply	other threads:[~2018-08-07 22:11 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-08-07 22:11 Dave Jiang [this message]
2018-08-07 22:11 ` [PATCH 2/2] [PATCH] xfs: Close race between direct IO and xfs_break_layouts() Dave Jiang
2018-08-08  8:53   ` Jan Kara
2018-08-08 15:47     ` Dave Jiang
2018-08-08  8:49 ` [PATCH 1/2] ext4: Close race between direct IO and ext4_break_layouts() Jan Kara

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