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| author | Tejun Heo <tj@kernel.org> | 2010-11-26 23:07:27 +0100 |
|---|---|---|
| committer | Rafael J. Wysocki <rjw@sisk.pl> | 2010-12-24 15:02:40 +0100 |
| commit | 8cfe400ca54fd1ed96f962bea5f7e20b09b6d69f (patch) | |
| tree | 393f1eb68d2497b04778c2e062fc4e1450df33eb /kernel | |
| parent | PM: Use proper ccflag flag in kernel/power/Makefile (diff) | |
| download | linux-8cfe400ca54fd1ed96f962bea5f7e20b09b6d69f.tar.xz linux-8cfe400ca54fd1ed96f962bea5f7e20b09b6d69f.zip | |
Freezer: Fix a race during freezing of TASK_STOPPED tasks
After calling freeze_task(), try_to_freeze_tasks() see whether the
task is stopped or traced and if so, considers it to be frozen;
however, nothing guarantees that either the task being frozen sees
TIF_FREEZE or the freezer sees TASK_STOPPED -> TASK_RUNNING
transition. The task being frozen may wake up and not see TIF_FREEZE
while the freezer fails to notice the transition and believes the task
is still stopped.
This patch fixes the race by making freeze_task() always go through
fake_signal_wake_up() for applicable tasks. The function goes through
the target task's scheduler lock and thus guarantees that either the
target sees TIF_FREEZE or try_to_freeze_task() sees TASK_RUNNING.
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/freezer.c | 9 | ||||
| -rw-r--r-- | kernel/power/process.c | 6 |
2 files changed, 13 insertions, 2 deletions
diff --git a/kernel/freezer.c b/kernel/freezer.c index bd1d42b17cb2..66ecd2ead215 100644 --- a/kernel/freezer.c +++ b/kernel/freezer.c @@ -104,8 +104,13 @@ bool freeze_task(struct task_struct *p, bool sig_only) } if (should_send_signal(p)) { - if (!signal_pending(p)) - fake_signal_wake_up(p); + fake_signal_wake_up(p); + /* + * fake_signal_wake_up() goes through p's scheduler + * lock and guarantees that TASK_STOPPED/TRACED -> + * TASK_RUNNING transition can't race with task state + * testing in try_to_freeze_tasks(). + */ } else if (sig_only) { return false; } else { diff --git a/kernel/power/process.c b/kernel/power/process.c index e50b4c1b2a0f..eb2c88a9e562 100644 --- a/kernel/power/process.c +++ b/kernel/power/process.c @@ -64,6 +64,12 @@ static int try_to_freeze_tasks(bool sig_only) * perturb a task in TASK_STOPPED or TASK_TRACED. * It is "frozen enough". If the task does wake * up, it will immediately call try_to_freeze. + * + * Because freeze_task() goes through p's + * scheduler lock after setting TIF_FREEZE, it's + * guaranteed that either we see TASK_RUNNING or + * try_to_stop() after schedule() in ptrace/signal + * stop sees TIF_FREEZE. */ if (!task_is_stopped_or_traced(p) && !freezer_should_skip(p)) |