linux-ext4 - [PATCH 5/5] ext4: add locking for O

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Message-Id: <1397322161-32148-6-git-send-email-tytso@mit.edu>
Date:	Sat, 12 Apr 2014 13:02:41 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Ext4 Developers List <linux-ext4@...r.kernel.org>
Cc:	viro@...IV.linux.org.uk, Theodore Ts'o <tytso@....edu>
Subject: [PATCH 5/5] ext4: add locking for O_APPEND writes

Al Viro pointed out that we need to make sure we only allow one
O_APPEND write to proceed at a time so that the the s_bitmap_maxbytes
check can be properly checked.

Signed-off-by: "Theodore Ts'o" <tytso@....edu>
---
 fs/ext4/file.c | 46 +++++++++++++++++++++++++++++-----------------
 1 file changed, 29 insertions(+), 17 deletions(-)

diff --git a/fs/ext4/file.c b/fs/ext4/file.c
index 7c8f483..c3824dd 100644
--- a/fs/ext4/file.c
+++ b/fs/ext4/file.c
@@ -98,24 +98,32 @@ ext4_file_write(struct kiocb *iocb, const struct iovec *iov,
 	struct file *file = iocb->ki_filp;
 	struct inode *inode = file_inode(iocb->ki_filp);
 	struct blk_plug plug;
+	struct mutex *aio_mutex = NULL;
 	int o_direct = file->f_flags & O_DIRECT;
-	int overwrite = 0;
+	int overwrite = 0, i_mutex_grabbed = 0;
 	size_t length = iov_length(iov, nr_segs);
 	ssize_t ret;
 
 	BUG_ON(iocb->ki_pos != pos);
 
+	if (file->f_flags & O_APPEND) {
+		mutex_lock(&inode->i_mutex);
+		i_mutex_grabbed = 1;
+		iocb->ki_pos = pos = i_size_read(inode);
+	}
+
 	/*
 	 * If we have encountered a bitmap-format file, the size limit
 	 * is smaller than s_maxbytes, which is for extent-mapped files.
 	 */
-
 	if (!(ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))) {
 		struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
 
 		if ((pos > sbi->s_bitmap_maxbytes ||
-		    (pos == sbi->s_bitmap_maxbytes && length > 0)))
-			return -EFBIG;
+		     (pos == sbi->s_bitmap_maxbytes && length > 0))) {
+			ret = -EFBIG;
+			goto errout;
+		}
 
 		if (pos + length > sbi->s_bitmap_maxbytes) {
 			nr_segs = iov_shorten((struct iovec *)iov, nr_segs,
@@ -123,19 +131,20 @@ ext4_file_write(struct kiocb *iocb, const struct iovec *iov,
 		}
 	}
 
-	if (o_direct) {
-		struct mutex *aio_mutex = NULL;
-
-		/* Unaligned direct AIO must be serialized; see comment above */
-		if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS) &&
-		    !is_sync_kiocb(iocb) &&
-		    ext4_unaligned_aio(inode, iov, nr_segs, pos)) {
-			aio_mutex = ext4_aio_mutex(inode);
-			mutex_lock(aio_mutex);
-			ext4_unwritten_wait(inode);
-		}
+	/* Unaligned direct AIO must be serialized; see comment above */
+	if (o_direct && ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS) &&
+	    !is_sync_kiocb(iocb) &&
+	    ext4_unaligned_aio(inode, iov, nr_segs, pos)) {
+		aio_mutex = ext4_aio_mutex(inode);
+		mutex_lock(aio_mutex);
+		ext4_unwritten_wait(inode);
+	}
 
+	if (!i_mutex_grabbed)
 		mutex_lock(&inode->i_mutex);
+	i_mutex_grabbed = 1;
+
+	if (o_direct) {
 		if (aio_mutex)
 			mutex_unlock(aio_mutex);
 		blk_start_plug(&plug);
@@ -170,11 +179,11 @@ ext4_file_write(struct kiocb *iocb, const struct iovec *iov,
 			if (err == len && (map.m_flags & EXT4_MAP_MAPPED))
 				overwrite = 1;
 		}
-	} else
-		mutex_lock(&inode->i_mutex);
+	}
 
 	ret = __generic_file_aio_write(iocb, iov, nr_segs, &iocb->ki_pos);
 	mutex_unlock(&inode->i_mutex);
+	i_mutex_grabbed = 0;
 
 	if (ret > 0) {
 		ssize_t err;
@@ -186,6 +195,9 @@ ext4_file_write(struct kiocb *iocb, const struct iovec *iov,
 	if (o_direct)
 		blk_finish_plug(&plug);
 
+errout:
+	if (i_mutex_grabbed)
+		mutex_unlock(&inode->i_mutex);
 	return ret;
 }
 
-- 
1.9.0

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