linux-kernel - [PATCH 4.4 50/51] ext4: fix a potential fiemap/page fault deadlock w/ inline

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Message-Id: <20190115154854.223069122@linuxfoundation.org>
Date:   Tue, 15 Jan 2019 17:35:46 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Theodore Tso <tytso@....edu>,
        stable@...nel.org
Subject: [PATCH 4.4 50/51] ext4: fix a potential fiemap/page fault deadlock w/ inline_data

4.4-stable review patch.  If anyone has any objections, please let me know.

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

From: Theodore Ts'o <tytso@....edu>

commit 2b08b1f12cd664dc7d5c84ead9ff25ae97ad5491 upstream.

The ext4_inline_data_fiemap() function calls fiemap_fill_next_extent()
while still holding the xattr semaphore.  This is not necessary and it
triggers a circular lockdep warning.  This is because
fiemap_fill_next_extent() could trigger a page fault when it writes
into page which triggers a page fault.  If that page is mmaped from
the inline file in question, this could very well result in a
deadlock.

This problem can be reproduced using generic/519 with a file system
configuration which has the inline_data feature enabled.

Signed-off-by: Theodore Ts'o <tytso@....edu>
Cc: stable@...nel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 fs/ext4/inline.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

--- a/fs/ext4/inline.c
+++ b/fs/ext4/inline.c
@@ -1861,12 +1861,12 @@ int ext4_inline_data_fiemap(struct inode
 	physical += (char *)ext4_raw_inode(&iloc) - iloc.bh->b_data;
 	physical += offsetof(struct ext4_inode, i_block);

-	if (physical)
-		error = fiemap_fill_next_extent(fieinfo, start, physical,
-						inline_len, flags);
 	brelse(iloc.bh);
 out:
 	up_read(&EXT4_I(inode)->xattr_sem);
+	if (physical)
+		error = fiemap_fill_next_extent(fieinfo, start, physical,
+						inline_len, flags);
 	return (error < 0 ? error : 0);
 }