Eric Sandeen wrote:
> Now that the filesystem freeze operation has been elevated
> to the VFS, and is just an ioctl away, some sort of safety net
> for unintentionally frozen root filesystems may be in order.
>
> The timeout thaw originally proposed did not get merged, but
> perhaps something like this would be useful in emergencies.
>
> For example, freeze /path/to/mountpoint may freeze your
> root filesystem if you forgot that you had that unmounted.
>
> I chose 'j' as the last remaining character other than 'h'
> which is sort of reserved for help (because help is generated
> on any unknown character).
>
> I've tested this on a non-root fs with multiple (nested) freezers,
> as well as on a system rendered unresponsive due to a frozen
> root fs.
>
> Thanks,
> -Eric
>
> Signed-off-by: Eric Sandeen <sandeen@xxxxxxxxxx>
> ---
>
> Index: linux-2.6/drivers/char/sysrq.c
> ===================================================================
> --- linux-2.6.orig/drivers/char/sysrq.c 2009-01-16 13:24:14.688575212 -0600
> +++ linux-2.6/drivers/char/sysrq.c 2009-01-16 13:26:35.232575643 -0600
> @@ -346,6 +346,17 @@ static struct sysrq_key_op sysrq_moom_op
> .enable_mask = SYSRQ_ENABLE_SIGNAL,
> };
>
> +static void sysrq_handle_thaw(int key, struct tty_struct *tty)
> +{
> + emergency_thaw_all();
> +}
> +static struct sysrq_key_op sysrq_thaw_op = {
> + .handler = sysrq_handle_thaw,
> + .help_msg = "Thaw(J)",
Can the help text be less terse, e.g.: "thaw-filesystems(J)" ?
Not capital-T Thaw because that was used to mean "use sysrq-T" to invoke
this sysrq.
> + .action_msg = "Emergency Thaw of all frozen filesystems",
> + .enable_mask = SYSRQ_ENABLE_SIGNAL,
> +};
> +
> static void sysrq_handle_kill(int key, struct tty_struct *tty)
> {
> send_sig_all(SIGKILL);
> @@ -396,9 +407,9 @@ static struct sysrq_key_op *sysrq_key_ta
> &sysrq_moom_op, /* f */
> /* g: May be registered by ppc for kgdb */
> NULL, /* g */
> - NULL, /* h */
> + NULL, /* h - reserved for help */
Yes, thanks.
> &sysrq_kill_op, /* i */
> - NULL, /* j */
> + &sysrq_thaw_op, /* j */
> &sysrq_SAK_op, /* k */
> #ifdef CONFIG_SMP
> &sysrq_showallcpus_op, /* l */
> Index: linux-2.6/fs/buffer.c
> ===================================================================
> --- linux-2.6.orig/fs/buffer.c 2009-01-16 13:24:15.564575078 -0600
> +++ linux-2.6/fs/buffer.c 2009-01-16 13:26:35.257575540 -0600
> @@ -258,6 +258,29 @@ struct super_block *freeze_bdev(struct b
> }
> EXPORT_SYMBOL(freeze_bdev);
>
> +void do_thaw_all(unsigned long unused)
> +{
> + struct super_block *sb;
> + char b[BDEVNAME_SIZE];
> +
> + list_for_each_entry(sb, &super_blocks, s_list) {
> + while (sb->s_bdev && !thaw_bdev(sb->s_bdev, sb))
> + printk(KERN_WARNING "Emergency Thaw on %s\n",
> + bdevname(sb->s_bdev, b));
> + }
> + printk(KERN_WARNING "Emergency Thaw complete\n");
> +}
> +
> +/**
> + * emergency_thaw_all -- forcibly thaw every frozen filesystem
> + *
> + * Used for emergency unfreeze of all filesystems via SysRq-z
-j
> + */
> +void emergency_thaw_all(void)
> +{
> + pdflush_operation(do_thaw_all, 0);
> +}
> +
> /**
> * thaw_bdev -- unlock filesystem
> * @bdev: blockdevice to unlock
--
~Randy
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