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sched/core: Introduce set_special_state()

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Gaurav reported a perceived problem with TASK_PARKED, which turned out
to be a broken wait-loop pattern in __kthread_parkme(), but the
reported issue can (and does) in fact happen for states that do not do
condition based sleeps.

When the 'current->state = TASK_RUNNING' store of a previous
(concurrent) try_to_wake_up() collides with the setting of a 'special'
sleep state, we can loose the sleep state.

Normal condition based wait-loops are immune to this problem, but for
sleep states that are not condition based are subject to this problem.

There already is a fix for TASK_DEAD. Abstract that and also apply it
to TASK_STOPPED and TASK_TRACED, both of which are also without
condition based wait-loop.

Reported-by: Gaurav Kohli <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Reviewed-by: Oleg Nesterov <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
This commit is contained in:
Peter Zijlstra 2018-04-30 14:51:01 +02:00 • committed by Ingo Molnar
commit b5bf9a90bb
4 changed files with 62 additions and 24 deletions
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17
kernel/signal.c
View file

@ -1961,14 +1961,27 @@ static void ptrace_stop(int exit_code, int why, int clear_code, siginfo_t *info)
return;
}
set_special_state(TASK_TRACED);
/*
* We're committing to trapping. TRACED should be visible before
* TRAPPING is cleared; otherwise, the tracer might fail do_wait().
* Also, transition to TRACED and updates to ->jobctl should be
* atomic with respect to siglock and should be done after the arch
* hook as siglock is released and regrabbed across it.
*
* TRACER TRACEE
*
* ptrace_attach()
* [L] wait_on_bit(JOBCTL_TRAPPING) [S] set_special_state(TRACED)
* do_wait()
* set_current_state() smp_wmb();
* ptrace_do_wait()
* wait_task_stopped()
* task_stopped_code()
* [L] task_is_traced() [S] task_clear_jobctl_trapping();
*/
set_current_state(TASK_TRACED);
smp_wmb();
current->last_siginfo = info;
current->exit_code = exit_code;
@ -2176,7 +2189,7 @@ static bool do_signal_stop(int signr)
if (task_participate_group_stop(current))
notify = CLD_STOPPED;
__set_current_state(TASK_STOPPED);
set_special_state(TASK_STOPPED);
spin_unlock_irq(&current->sighand->siglock);
/*