filesystem freeze: allow SysRq emergency thaw to thaw frozen filesystems
commitc2d7543851849a6923680cdd7e1047ed1a84a1c5
authorEric Sandeen <sandeen@redhat.com>
Tue, 31 Mar 2009 22:23:46 +0000 (31 15:23 -0700)
committerLinus Torvalds <torvalds@linux-foundation.org>
Wed, 1 Apr 2009 15:59:17 +0000 (1 08:59 -0700)
treebf3038819d4be83a1d1e64d7b95bbb3d9d908544
parent55a63998b8967615a15e2211ba0ff3a84a565824
filesystem freeze: allow SysRq emergency thaw to thaw frozen filesystems

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.

[randy.dunlap@oracle.com: emergency thaw only if CONFIG_BLOCK enabled]
Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Cc: Takashi Sato <t-sato@yk.jp.nec.com>
Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Documentation/sysrq.txt
drivers/char/sysrq.c
fs/buffer.c
include/linux/fs.h