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SubjectRe: [PATCH] fs: record task name which froze superblock
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@gmail.com>
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?

> ---
>
> 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;
Why don't you just set the name in ioctl_fsfreeze() in both cases?
Also you seem to be missing freezing / thawing in freeze/thaw_bdev()
functions.

> }
>
> 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];
Here should be TASK_COMM_LEN, shouldn't it?

Honza
--
Jan Kara <jack@suse.cz>
SUSE Labs, CR


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