There are 4 state transitions possible for a freezer. Only FREEZING -> FROZEN transaction is done lazily. This patch allows update_freezer_state only to perform this transaction and renames the function to update_if_frozen.
Moreover is_task_frozen_enough function is removed and its every occurence is replaced with frozen(). Therefore for a group to become FROZEN every task must be frozen. The previous version could trigger a following bug: When cgroup is in the process of freezing (but none of its tasks are frozen yet), update_freezer_state() (called from freezer_read or freezer_write) would incorrectly report that a group is 'THAWED' (because nfrozen = 0), allowing the transaction FREEZING -> THAWED without writing anything to 'freezer.state'. This is incorrect according to the documentation. This could result in a 'THAWED' cgroup with frozen tasks inside. A code to reproduce this bug is available here: http://pentium.hopto.org/~thinred/repos/linux-misc/freezer_bug2.c Signed-off-by: Tomasz Buchert <[email protected]> --- kernel/cgroup_freezer.c | 40 +++++++++++++++++----------------------- 1 files changed, 17 insertions(+), 23 deletions(-) diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c index c287627..a5f7cb6 100644 --- a/kernel/cgroup_freezer.c +++ b/kernel/cgroup_freezer.c @@ -153,13 +153,6 @@ static void freezer_destroy(struct cgroup_subsys *ss, kfree(cgroup_freezer(cgroup)); } -/* Task is frozen or will freeze immediately when next it gets woken */ -static bool is_task_frozen_enough(struct task_struct *task) -{ - return frozen(task) || - (task_is_stopped_or_traced(task) && freezing(task)); -} - /* * The call to cgroup_lock() in the freezer.state write method prevents * a write to that file racing against an attach, and hence the @@ -236,31 +229,32 @@ static void freezer_fork(struct cgroup_subsys *ss, struct task_struct *task) /* * caller must hold freezer->lock */ -static void update_freezer_state(struct cgroup *cgroup, +static void update_if_frozen(struct cgroup *cgroup, struct freezer *freezer) { struct cgroup_iter it; struct task_struct *task; unsigned int nfrozen = 0, ntotal = 0; + enum freezer_state old_state = freezer->state; cgroup_iter_start(cgroup, &it); while ((task = cgroup_iter_next(cgroup, &it))) { ntotal++; - if (is_task_frozen_enough(task)) + if (frozen(task)) nfrozen++; } - /* - * Transition to FROZEN when no new tasks can be added ensures - * that we never exist in the FROZEN state while there are unfrozen - * tasks. - */ - if (nfrozen == ntotal) - freezer->state = CGROUP_FROZEN; - else if (nfrozen > 0) - freezer->state = CGROUP_FREEZING; - else - freezer->state = CGROUP_THAWED; + if (old_state == CGROUP_THAWED) { + BUG_ON(nfrozen > 0); + } + else if (old_state == CGROUP_FREEZING) { + if (nfrozen == ntotal) + freezer->state = CGROUP_FROZEN; + } + else { /* old_state == CGROUP_FROZEN */ + BUG_ON(nfrozen != ntotal); + } + cgroup_iter_end(cgroup, &it); } @@ -279,7 +273,7 @@ static int freezer_read(struct cgroup *cgroup, struct cftype *cft, if (state == CGROUP_FREEZING) { /* We change from FREEZING to FROZEN lazily if the cgroup was * only partially frozen when we exitted write. */ - update_freezer_state(cgroup, freezer); + update_if_frozen(cgroup, freezer); state = freezer->state; } spin_unlock_irq(&freezer->lock); @@ -301,7 +295,7 @@ static int try_to_freeze_cgroup(struct cgroup *cgroup, struct freezer *freezer) while ((task = cgroup_iter_next(cgroup, &it))) { if (!freeze_task(task, true)) continue; - if (is_task_frozen_enough(task)) + if (frozen(task)) continue; if (!freezing(task) && !freezer_should_skip(task)) num_cant_freeze_now++; @@ -335,7 +329,7 @@ static int freezer_change_state(struct cgroup *cgroup, spin_lock_irq(&freezer->lock); - update_freezer_state(cgroup, freezer); + update_if_frozen(cgroup, freezer); if (goal_state == freezer->state) goto out; -- 1.6.3.3 _______________________________________________ Containers mailing list [email protected] https://lists.linux-foundation.org/mailman/listinfo/containers _______________________________________________ Devel mailing list [email protected] https://openvz.org/mailman/listinfo/devel
