[PATCH] fs: record task name which froze superblock

[Alexey Dobriyan]

Freezing and thawing are separate system calls, task which is supposed
to thaw filesystem/superblock can disappear due to crash or not thaw
due to a bug. Record at least task name (we can't take task_struct
reference) to make support engineer's life easier.

Hopefully 16 bytes per superblock isn't much.

P.S.: Cc'ing GFS2 people just in case they want to correct
my understanding of GFS2 having async freeze code.

Signed-off-by: Alexey Dobriyan <adobriyan@xxxxxxxxx>
---

 fs/ioctl.c         |   22 ++++++++++++++++------
 fs/super.c         |    2 ++
 include/linux/fs.h |    2 ++
 3 files changed, 20 insertions(+), 6 deletions(-)

--- a/fs/ioctl.c
+++ b/fs/ioctl.c
@@ -518,6 +518,7 @@ static int ioctl_fioasync(unsigned int fd, struct file *filp,
 static int ioctl_fsfreeze(struct file *filp)
 {
 	struct super_block *sb = file_inode(filp)->i_sb;
+	int rv;
 
 	if (!capable(CAP_SYS_ADMIN))
 		return -EPERM;
@@ -527,22 +528,31 @@ static int ioctl_fsfreeze(struct file *filp)
 		return -EOPNOTSUPP;
 
 	/* Freeze */
-	if (sb->s_op->freeze_super)
-		return sb->s_op->freeze_super(sb);
-	return freeze_super(sb);
+	if (sb->s_op->freeze_super) {
+		rv = sb->s_op->freeze_super(sb);
+		if (rv == 0)
+			get_task_comm(sb->s_writers.freeze_comm, current);
+	} else
+		rv = freeze_super(sb);
+	return rv;
 }
 
 static int ioctl_fsthaw(struct file *filp)
 {
 	struct super_block *sb = file_inode(filp)->i_sb;
+	int rv;
 
 	if (!capable(CAP_SYS_ADMIN))
 		return -EPERM;
 
 	/* Thaw */
-	if (sb->s_op->thaw_super)
-		return sb->s_op->thaw_super(sb);
-	return thaw_super(sb);
+	if (sb->s_op->thaw_super) {
+		rv = sb->s_op->thaw_super(sb);
+		if (rv == 0)
+			memset(sb->s_writers.freeze_comm, 0, TASK_COMM_LEN);
+	} else
+		rv = thaw_super(sb);
+	return rv;
 }
 
 /*
--- a/fs/super.c
+++ b/fs/super.c
@@ -1355,6 +1355,7 @@ int freeze_super(struct super_block *sb)
 	 * sees write activity when frozen is set to SB_FREEZE_COMPLETE.
 	 */
 	sb->s_writers.frozen = SB_FREEZE_COMPLETE;
+	get_task_comm(sb->s_writers.freeze_comm, current);
 	up_write(&sb->s_umount);
 	return 0;
 }
@@ -1391,6 +1392,7 @@ int thaw_super(struct super_block *sb)
 
 out:
 	sb->s_writers.frozen = SB_UNFROZEN;
+	memset(sb->s_writers.freeze_comm, 0, TASK_COMM_LEN);
 	smp_wmb();
 	wake_up(&sb->s_writers.wait_unfrozen);
 	deactivate_locked_super(sb);
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1221,6 +1221,8 @@ struct sb_writers {
 	int			frozen;		/* Is sb frozen? */
 	wait_queue_head_t	wait_unfrozen;	/* queue for waiting for
 						   sb to be thawed */
+	/* who froze superblock */
+	char			freeze_comm[16];
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 	struct lockdep_map	lock_map[SB_FREEZE_LEVELS];
 #endif
--
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