90e362f4a7
Chris bisected a NULL pointer deference in task_sched_runtime() to commit6e998916df'sched/cputime: Fix clock_nanosleep()/clock_gettime() inconsistency'. Chris observed crashes in atop or other /proc walking programs when he started fork bombs on his machine. He assumed that this is a new exit race, but that does not make any sense when looking at that commit. What's interesting is that, the commit provides update_curr callbacks for all scheduling classes except stop_task and idle_task. While nothing can ever hit that via the clock_nanosleep() and clock_gettime() interfaces, which have been the target of the commit in question, the author obviously forgot that there are other code paths which invoke task_sched_runtime() do_task_stat(() thread_group_cputime_adjusted() thread_group_cputime() task_cputime() task_sched_runtime() if (task_current(rq, p) && task_on_rq_queued(p)) { update_rq_clock(rq); up->sched_class->update_curr(rq); } If the stats are read for a stomp machine task, aka 'migration/N' and that task is current on its cpu, this will happily call the NULL pointer of stop_task->update_curr. Ooops. Chris observation that this happens faster when he runs the fork bomb makes sense as the fork bomb will kick migration threads more often so the probability to hit the issue will increase. Add the missing update_curr callbacks to the scheduler classes stop_task and idle_task. While idle tasks cannot be monitored via /proc we have other means to hit the idle case. Fixes:6e998916df'sched/cputime: Fix clock_nanosleep()/clock_gettime() inconsistency' Reported-by: Chris Mason <clm@fb.com> Reported-and-tested-by: Borislav Petkov <bp@alien8.de> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@kernel.org> Cc: Stanislaw Gruszka <sgruszka@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
137 lines
2.9 KiB
C
137 lines
2.9 KiB
C
#include "sched.h"
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/*
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* stop-task scheduling class.
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*
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* The stop task is the highest priority task in the system, it preempts
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* everything and will be preempted by nothing.
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*
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* See kernel/stop_machine.c
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*/
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#ifdef CONFIG_SMP
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static int
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select_task_rq_stop(struct task_struct *p, int cpu, int sd_flag, int flags)
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{
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return task_cpu(p); /* stop tasks as never migrate */
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}
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#endif /* CONFIG_SMP */
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static void
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check_preempt_curr_stop(struct rq *rq, struct task_struct *p, int flags)
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{
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/* we're never preempted */
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}
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static struct task_struct *
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pick_next_task_stop(struct rq *rq, struct task_struct *prev)
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{
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struct task_struct *stop = rq->stop;
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if (!stop || !task_on_rq_queued(stop))
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return NULL;
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put_prev_task(rq, prev);
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stop->se.exec_start = rq_clock_task(rq);
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return stop;
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}
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static void
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enqueue_task_stop(struct rq *rq, struct task_struct *p, int flags)
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{
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add_nr_running(rq, 1);
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}
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static void
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dequeue_task_stop(struct rq *rq, struct task_struct *p, int flags)
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{
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sub_nr_running(rq, 1);
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}
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static void yield_task_stop(struct rq *rq)
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{
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BUG(); /* the stop task should never yield, its pointless. */
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}
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static void put_prev_task_stop(struct rq *rq, struct task_struct *prev)
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{
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struct task_struct *curr = rq->curr;
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u64 delta_exec;
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delta_exec = rq_clock_task(rq) - curr->se.exec_start;
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if (unlikely((s64)delta_exec < 0))
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delta_exec = 0;
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schedstat_set(curr->se.statistics.exec_max,
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max(curr->se.statistics.exec_max, delta_exec));
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curr->se.sum_exec_runtime += delta_exec;
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account_group_exec_runtime(curr, delta_exec);
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curr->se.exec_start = rq_clock_task(rq);
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cpuacct_charge(curr, delta_exec);
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}
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static void task_tick_stop(struct rq *rq, struct task_struct *curr, int queued)
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{
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}
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static void set_curr_task_stop(struct rq *rq)
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{
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struct task_struct *stop = rq->stop;
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stop->se.exec_start = rq_clock_task(rq);
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}
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static void switched_to_stop(struct rq *rq, struct task_struct *p)
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{
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BUG(); /* its impossible to change to this class */
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}
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static void
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prio_changed_stop(struct rq *rq, struct task_struct *p, int oldprio)
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{
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BUG(); /* how!?, what priority? */
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}
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static unsigned int
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get_rr_interval_stop(struct rq *rq, struct task_struct *task)
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{
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return 0;
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}
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static void update_curr_stop(struct rq *rq)
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{
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}
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/*
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* Simple, special scheduling class for the per-CPU stop tasks:
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*/
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const struct sched_class stop_sched_class = {
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.next = &dl_sched_class,
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.enqueue_task = enqueue_task_stop,
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.dequeue_task = dequeue_task_stop,
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.yield_task = yield_task_stop,
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.check_preempt_curr = check_preempt_curr_stop,
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.pick_next_task = pick_next_task_stop,
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.put_prev_task = put_prev_task_stop,
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#ifdef CONFIG_SMP
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.select_task_rq = select_task_rq_stop,
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#endif
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.set_curr_task = set_curr_task_stop,
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.task_tick = task_tick_stop,
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.get_rr_interval = get_rr_interval_stop,
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.prio_changed = prio_changed_stop,
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.switched_to = switched_to_stop,
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.update_curr = update_curr_stop,
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};
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