freezer: add missing mb's to freezer_count() and freezer_should_skip()
authorTejun Heo <tj@kernel.org>
Tue, 16 Oct 2012 22:03:14 +0000 (15:03 -0700)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Fri, 11 Jan 2013 17:06:58 +0000 (09:06 -0800)
commitcd924e960d3c2ae1654109b5b9e88cec334f7126
treeed7bec78c3e2930df0c86d44aae32d2c4dddb23f
parent475261dbbf5d85e1a298886385d859ada787ae1f
freezer: add missing mb's to freezer_count() and freezer_should_skip()

commit dd67d32dbc5de299d70cc9e10c6c1e29ffa56b92 upstream.

A task is considered frozen enough between freezer_do_not_count() and
freezer_count() and freezers use freezer_should_skip() to test this
condition.  This supposedly works because freezer_count() always calls
try_to_freezer() after clearing %PF_FREEZER_SKIP.

However, there currently is nothing which guarantees that
freezer_count() sees %true freezing() after clearing %PF_FREEZER_SKIP
when freezing is in progress, and vice-versa.  A task can escape the
freezing condition in effect by freezer_count() seeing !freezing() and
freezer_should_skip() seeing %PF_FREEZER_SKIP.

This patch adds smp_mb()'s to freezer_count() and
freezer_should_skip() such that either %true freezing() is visible to
freezer_count() or !PF_FREEZER_SKIP is visible to
freezer_should_skip().

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Rafael J. Wysocki <rjw@sisk.pl>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
include/linux/freezer.h