Re: [PATCH] fs: record task name which froze superblock

From: Steven Whitehouse
Date: Wed Feb 18 2015 - 05:18:26 EST


On 18/02/15 09:13, Jan Kara wrote:
On Wed 18-02-15 10:34:55, Alexey Dobriyan wrote:
On Mon, Feb 16, 2015 at 10:38:52AM +0100, Jan Kara wrote:
On Sat 14-02-15 21:55:24, Alexey Dobriyan wrote:
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>
Hum, and when do you show the task name? Or do you expect that customer
takes a crashdump and support just finds it in memory?
Yeah, having at least something in crashdump is fine.
OK, then comment about this at freeze_comm[] definition so that it's
clear it isn't just set-but-never-read field.
--- 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)
/* 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;
Why don't you just set the name in ioctl_fsfreeze() in both cases?
There are users of freeze_super() in GFS2 unless I'm misreading code.
Yes, there are. The call in fs/gfs2/glops.c is in a call path from
->freeze_super() handler for GFS2 so that one is handled in
ioctl_fsfreeze() anyway. The call in fs/gfs2/sys.c is a way to freeze
filesystem via sysfs (dunno why GFS2 has to invent its own thing and ioctl
isn't enough). Steven? So having the logic in ioctl_fsfreeze(),
freeze_bdev() and freeze_store() in gfs2 seems to be enough.

The sysfs freeze thing is historical and strongly deprecated - I hope that we may be able to remove it one day,


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