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Date: Fri, 17 May 2013 05:24:15 +0200
From: "Yuan Fu" <yuan.fu@....cn>
To: dmonakhov@...nvz.org, linux-ext4@...r.kernel.org
Subject: Re: [PATCH 1/4] ext4: Fix fsync error handling after filesysteb abort.
Dear Dmitry Monakhov,
I see a race condition,
__ext4_abort()
...
EXT4_SB(sb)->s_mount_flags |= EXT4_MF_FS_ABORTED;
...
smp_wmb()
[if scheduled at this point ]
...
sb->s_flags |= MS_RDONLY;
if schedule occur above point(in red). There comes race condition
the s_mount_flags set to EXT4_MF_FS_ABORTED. On the other hand
sb->s_flags is not set to MS_RDONLY. Now if ext4_fsync_file() is
called from some process, the check s_flags to MS_RDONLY will fail,
and it will flush unwritten io and not return -EORFS.
thanks
----- Original Message -----
From: Dmitry Monakhov
Sent: 05/16/13 05:58 PM
Subject: [PATCH 1/4] ext4: Fix fsync error handling after filesysteb abort.
If filesystem was aborted after inode's write back complete
but before it's metadata was updated we may return success
due to (sb->s_flags & MS_RDONLY) which is incorrect and
result in data loss.
In order to handle fs abort correctly we have to check
fs state once we discover that it is in MS_RDONLY state
Test case: http://patchwork.ozlabs.org/patch/244297/
Signed-off-by: Dmitry Monakhov <dmonakhov@...nvz.org>
---
fs/ext4/fsync.c | 8 ++++++--
fs/ext4/super.c | 13 ++++++++++++-
2 files changed, 18 insertions(+), 3 deletions(-)
diff --git a/fs/ext4/fsync.c b/fs/ext4/fsync.c
index e0ba8a4..d7df2f1 100644
--- a/fs/ext4/fsync.c
+++ b/fs/ext4/fsync.c
@@ -129,9 +129,13 @@ int ext4_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
return ret;
mutex_lock(&inode->i_mutex);
- if (inode->i_sb->s_flags & MS_RDONLY)
+ if (inode->i_sb->s_flags & MS_RDONLY) {
+ /* Make shure that we read updated s_mount_flags value */
+ smp_rmb();
+ if (EXT4_SB(inode->i_sb)->s_mount_flags & EXT4_MF_FS_ABORTED)
+ ret = -EROFS;
goto out;
-
+ }
ret = ext4_flush_unwritten_io(inode);
if (ret < 0)
goto out;
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index dbc7c09..6c91c8e 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -398,6 +398,11 @@ static void ext4_handle_error(struct super_block *sb)
}
if (test_opt(sb, ERRORS_RO)) {
ext4_msg(sb, KERN_CRIT, "Remounting filesystem read-only");
+ /*
+ * Make shure updated value of ->s_mount_flags will be visiable
+ * before ->s_flags update
+ */
+ smp_wmb();
sb->s_flags |= MS_RDONLY;
}
if (test_opt(sb, ERRORS_PANIC))
@@ -552,6 +557,7 @@ void __ext4_std_error(struct super_block *sb, const char *function,
*
* We unconditionally force the filesystem into an ABORT|READONLY state,
* unless the error response on the fs has been set to panic in which
+
* case we take the easy way out and panic immediately.
*/
@@ -570,8 +576,13 @@ void __ext4_abort(struct super_block *sb, const char *function,
if ((sb->s_flags & MS_RDONLY) == 0) {
ext4_msg(sb, KERN_CRIT, "Remounting filesystem read-only");
- sb->s_flags |= MS_RDONLY;
EXT4_SB(sb)->s_mount_flags |= EXT4_MF_FS_ABORTED;
+ /*
+ * Make shure updated value of ->s_mount_flags will be visiable
+ * before ->s_flags update
+ */
+ smp_wmb();
+ sb->s_flags |= MS_RDONLY;
if (EXT4_SB(sb)->s_journal)
jbd2_journal_abort(EXT4_SB(sb)->s_journal, -EIO);
save_error_info(sb, function, line);
--
1.7.1
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